Audio amplifiers

Audio amplifiers

An audio amplifier is a device used to amplify audio signals of frequency range from 16Hz to 20 kHz. Two types:

1. Voltage amplifier

2. Power amplifier

Voltage amplifiers are used as pre-amplifiers, buffer amplifier (or intermediate amplifiers) and driver amplifier. Their main function is to amplify the audio signal voltages in staged ,so that finally the driver gives an output voltage sufficient to reduce the resistance of the power amplifier and hence , to drive it to give power amplification.

The final amplification stage always involves a power amplifier which feed audio power to loudspeakers for conversion of electrical signals into sound waves.

Characteristics of audio amplifiers:

1.      Gain: Ratio of output to input signal is called gain of an amplifier. It is expressed in decibels(dB)

Voltage gain (A­_v) = 20log

Power gain (A_p) = 10log

Where V2 and v1 are output and input voltages respectively, and P2 and P1 are output and input power respectively.

The typical gain of a voltage amplifier is about 60dB. The typical gain of a power amplifier is about 20dB. Higher the level of input signal, less is the gain.

2.      Bandwidth: An audio amplifier should pass the whole audible frequency range which is from 16Hz to 20 kHz known as bandwidth of audio amplifier.

3.      Distortion : An amplifier can suffer from the following types of distortions:

i)                    Frequency Distortion: When all the audio frequencies are not simplified equally well, it causes frequency distortion.

ii)                  Phase Distortion: When the relative phase relationship as in the input signal is not maintained in the output signal, it causes phase distortion

iii)                Amplitude distortion: It is caused due to passage of signal through non-linear portion of the characteristics curve of transistors.

# Amplifier quality is characterized by a list of specifications that include:
·         Gain, the ratio between the magnitude of output and input signals
·         Bandwidth, the width of the useful frequency range
·         Efficiency, the ratio between the power of the output and total power consumption
·         Linearity, the degree of proportionality between input and output
·         Noise, a measure of undesired noise mixed into the output
·         Output dynamic range, the ratio of the largest and the smallest useful output levels
·         Slew rate, the maximum rate of change of the output
·         Rise time, settling time, ringing and overshoot that characterize the step response
·         Stability, the ability to avoid self-oscillation

Video amplifiers

These deal with video signals and have varying bandwidths depending on whether the video signal is for SDTV, EDTV, HDTV 720p or 1080i/p etc... The specification of the bandwidth itself depends on what kind of filter is used—and at which point (-1 dB or -3 dB for example) the bandwidth is measured.

Not all amplifiers are the same and are therefore classified according to their circuit configurations and methods of operation. In “Electronics”, small signal amplifiers are commonly used devices as they have the ability to amplify a relatively small input signal, for example from a Sensor such as a photo-device, into a much larger output signal to drive a relay, lamp or loudspeaker for example.

The type or classification of an amplifier is given in the following table.

Classification of Amplifiers

Type of Signal	Type of Configuration	Classification	Frequency of Operation
Small Signal	Common Emitter	Class A Amplifier	Direct Current (DC)
Large Signal	Common Base	Class B Amplifier	Audio Frequencies (AF)
	Common Collector	Class AB Amplifier	Radio Frequencies (RF)
		Class C Amplifier	VHF, UHF and SHF Frequencies

The small signal model accounts for the behavior which is linear around an operating point. When the signal is large in amplitude (say more than 1/5 of VCC, a rule of thumb) the behavior becomes nonlinear and we have to use the model which accounts for non-linearity, and thus called large signal model.

In small signal noise is important, efficiency is not. In large signal it is the opposite. Small signal is linear and so the parameters can be calculated from two port parameters or equivalent RLC-generator circuit.
In large signal case the time domain simulation is needed to find the effects of nonlinearities and a Fourier analysis is done of the results to get the amplitude and phase of the fundamental and harmonic amplitudes and input impedance.
Very costly simulators have very complex models for the transistors and can do frequency domain type calculations and get the harmonic effects at the same time.

Types of microphones and speakers

A microphone, colloquially mic or mike (/ˈmark/), is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal.
Most microphones today use electromagnetic induction (dynamic microphones), capacitance change (condenser microphones) or piezoelectricity (piezoelectric microphones) to produce an electrical signal from air pressure variations. Microphones typically need to be connected to a preamplifier before the signal can be amplified with an audio power amplifier and a speaker or recorded.
It is often taught that "sound is vibrations in the air." We are able to enjoy music because we sense these vibrations in the air as sound.
Microphones convert these vibrations into electrical signals. Here are the two main types of microphone:

(1) Dynamic microphones

.

(2)Condenser microphone

Dynamic Microphones

Dynamic microphones are versatile and ideal for general-purpose use. They use a simple design with few moving parts. They are relatively sturdy and resilient to rough handling. They are also better suited to handling high volume levels, such as from certain musical instruments or amplifiers. They have no internal amplifier and do not require batteries or external power.

How Dynamic Microphones Work

As you may recall from your school science, when a magnet is moved near a coil of wire an electrical current is generated in the wire. Using this electromagnet principle, the dynamic microphone uses a wire coil and magnet to create the audio signal.

The diaphragm is attached to the coil. When the diaphragm vibrates in response to incoming sound waves, the coil moves backwards and forwards past the magnet. This creates a current in the coil which is channeled from the microphone along wires. A common configuration is shown below.

Cross-Section of a Typical Condenser Microphone

Characteristics

-Construction is simple and comparatively sturdy. 
-No power supply is required. 
-Relatively inexpensive.

 

Condenser microphone

The condenser microphone, is also called a capacitor microphone or electrostatic microphone—capacitors were historically called condensers.

Condenser Microphones

Condenser means capacitor, an electronic component which stores energy in the form of an electrostatic field. The term condenser is actually obsolete but has stuck as the name for this type of microphone, which uses a capacitor to convert acoustical energy into electrical energy.

Condenser microphones require power from a battery or external source. The resulting audio signal is stronger signal than that from a dynamic. Condensers also tend to be more sensitive and responsive than dynamics, making them well-suited to capturing subtle nuances in a sound. They are not ideal for high-volume work, as their sensitivity makes them prone to distort.

How Condenser Microphones Work

A capacitor has two plates with a voltage between them. In the condenser mic, one of these plates is made of very light material and acts as the diaphragm. The diaphragm vibrates when struck by sound waves, changing the distance between the two plates and therefore changing the capacitance. Specifically, when the plates are closer together, capacitance increases and a charge current occurs. When the plates are further apart, capacitance decreases and a discharge current occurs.

A voltage is required across the capacitor for this to work. This voltage is supplied either by a battery in the mic or by external phantom power.

Characteristics

-Good sensitivity at all frequencies. 
-Power supply is required. 
-Vulnerable to structural vibration and humidity

Quality of AM and FM reception

AM (or Amplitude Modulation) and FM (or Frequency Modulation) are ways of broadcasting radio signals. Both transmit the information in the form of electromagnetic waves. AM works by modulating (varying) the amplitude of the signal or carrier transmitted according to the information being sent, while the frequency remains constant. This differs from FM technology in which information (sound) is encoded by varying the frequency of the wave and the amplitude is kept constant.

Comparison chart

	AM	FM
Stands for	AM stands for Amplitude Modulation	FM stands for Frequency Modulation
Origin	AM method of audio transmission was first successfully carried out in the mid-1870s.	FM radio was developed in the United states in the 1930s, mainly by Edwin Armstrong.
Modulating differences	In AM, a radio wave known as the "carrier" or "carrier wave" is modulated in amplitude by the signal that is to be transmitted. The frequency and phase remain the same.	In FM, a radio wave known as the "carrier" or "carrier wave" is modulated in frequency by the signal that is to be transmitted. The amplitude and phase remain the same.
Pros and cons	AM has poorer sound quality compared with FM, but is cheaper and can be transmitted over long distances. It has a lower bandwidth so it can have more stations available in any frequency range.	FM is less prone to interference than AM. However, FM signals are impacted by physical barriers. FM has better sound quality due to higher bandwidth.
Frequency Range	AM radio ranges from 535 to 1705 KHz (OR) Up to 1200 bits per second.	FM radio ranges in a higher spectrum from 88 to 108 MHz (OR) 1200 to 2400 bits per second.
Bandwidth Requirements	Twice the highest modulating frequency. In AM radio broadcasting, the modulating signal has bandwidth of 15kHz, and hence the bandwidth of an amplitude-modulated signal is 30kHz.	Twice the sum of the modulating signal frequency and the frequency deviation. If the frequency deviation is 75kHz and the modulating signal frequency is 15kHz, the bandwidth required is 180kHz.
Zero crossing in modulated signal	Equidistant	Not equidistant
Complexity	Transmitter and receiver are simple but synchronization is needed in case of SSBSC AM carrier.	Transmitter and receiver are more complex as variation of modulating signal has to be converted and detected from corresponding variation in frequencies.(i.e. voltage to frequency and frequency to voltage conversion has to be done).
Noise	AM is more susceptible to noise because noise affects amplitude, which is where information is "stored" in an AM signal.	FM is less susceptible to noise because information in an FM signal is transmitted through varying the frequency, and not the amplitude

1.      Evolution:

Formulated in the 1870s, AM is a relatively older modulation process compared to FM which was found in the 1930s by Edwin Armstrong.

2.      Technology:

AM stands for amplitude modulation where the amplitude of the carrier is modulated as per the message signal? The other aspects of the carrier wave such as frequency phase etc. remain constant. On the other hand, FM means frequency modulation and in it only frequency of the carrier wave changes while amplitude, phase etc. remain constant.

3.      Frequency range of working:

Amplitude modulation works between 540-1650 KHz while FM works at 88-108MHz.

4.      Power Consumption:

FM based signal transmission consumes a higher amount of power than an equivalent AM based signal transmission system.

5.      AM vs. FM: Signal Quality:

Signal quality is a lot superior in FM than AM as amplitude based signals are more susceptible to noise than those which use frequency.  Moreover, noise signals are difficult to filter out in AM reception whereas FM receivers easily filter out noise using the capture effect and pre-emphasis, de-emphasis effects. In capture effect, the receiver locks itself to catch stronger signal so that signals received are more synced with that at the transmitting end.

In pre-emphasis, de-emphasis process, the signal is further amplified to a higher frequency at sending end (pre-emphasis) and vice versa at receiver end (de-emphasis). These two processes reduce down the chances of a signal to get mixed with other signals and make FM more immune to noise than AM.

6.      Fading:

Fading refers to power variation during signal transmission. Due to fading, the power with the signal received can vary significantly and reception wouldn’t be of a good quality. Fading is more prominent in amplitude modulation as compared to frequency modulation. That is why, AM radio channels often face the problem where sound intensity varies while FM radio channels have constant good reception.

7.      Wavelength Difference between AM and FM:

AM waves work in the range of KHz while in FM waves work in MHz range. As a result, AM waves have a higher wavelength than the FM ones. A higher wavelength increases the range of AM signals as compared to FM which have a limited area of coverage.

8.      Bandwidth consumption:

AM signals consume 30 KHz of bandwidth for each while in FM 80 KHz is the bandwidth consumed by each signal? Hence, over a limited range of bandwidth, more number of signals can be sent in AM than FM.

9.      Circuit Complexity:

Aforesaid, Amplitude Modulation is an older process and has a very simple circuitry. On the other hand, frequency modulation requires a complicated circuitry for transmission and reception of signal. The signals sent in FM are more modulated and emphasized at the transmitter and they are thoroughly checked and corrected at the receiving end. This is why circuitry for FM signals is very complicated.

10.  Commercial Aspects:

Setting up an AM based radio communication system is very economic as there is no complicated circuitry and processes are easy to understand.

A few radios come with AM and FM functionality

On the other hand, FM is a fairly complicated communication system and requires high capital investment and expertise at work.  Commercially FM based radio systems are more popular due to high signal quality (especially audio) and more immunity to noise.

Stereo and mono sound reproduction systems

Stereo (or Stereophonic sound) is the reproduction of sound using two or more independent audio channels in a way that creates the impression of sound heard from various directions, as in natural hearing.  Mono (Monaural or monophonic sound reproduction) has audio in a single channel, often centered in the “sound field “.

Stereo sound has almost completely replaced mono because of the improved audio quality that stereo provides.

Comparison chart

	Mono	Stereo
Cost	Less expensive for recording and reproduction	More expensive for recording and reproduction
Recording	Easy to record, requires only basic equipment	Requires technical knowledge and skill to record, apart from equipment. It's important to know the relative position of the objects and events.
Key feature	Audio signals are routed through a single channel	Audio signals are routed through 2 or more channels to simulate depth/direction perception, like in the real world.
Stands for	Monaural or monophonic sound	Stereophonic sound
Usage	Public address system, radio talk shows, hearing aid, telephone and mobile communication, some AM radio stations	Movies, Television, Music players, FM radio stations

 Sound recording and reproduction is an electrical or mechanical inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects. The two main classes of sound recording technology are analog recording and digital recording.

Acoustic analog recording is achieved by a small microphone diaphragm that can detect changes in atmospheric pressure (acoustic sound waves) and record them as a graphic representation of the sound waves on a medium such as a phonograph

Digital recording and reproduction converts the analog sound signal picked up by the microphone to a digital form by the process of digitization.

Digital audio and compression techniques

Digital audio is technology that can be used to record, store, generate, manipulate, and reproduce sound using audio signals encoded in digital form.

A microphone converts sound to an analog electrical signal, then an analog-to-digital converter (ADC)—typically using pulse-code modulation—converts the analog signal into a digital signal. A digital-to-analog converter performs the reverse process, converting a digital signal back into an analog signal, which analog circuits amplify and send to a loudspeaker.

Digital audio systems may include compression, storage, processing  and transmission  components. Conversion to a digital format allows convenient manipulation, storage, transmission and retrieval of an audio signal.

Dynamic range compression (DRC) or simply compression is an electronic effect unit that reduces the volume of loud sounds or amplifies quiet sounds by narrowing or "compressing" an audio signal's dynamic range. Compression is commonly used in sound recording and reproduction, broadcasting, live sound at music concerts and in some instrument amplifiers  (usually bass amps).

Audio compression reduces loud sounds which are above a certain threshold while quiet sounds remain unaffected. In the 2000s, compressors are also available in audio software for recording. The dedicated electronic hardware unit or audio software used to apply compression is called a compressor.

 

Types

Two main methods of dynamic range reduction

Fig: Downward compression

Fig: Upward compression

Downward compression reduces loud sounds over a certain threshold while quiet sounds remain unaffected.

Upward compression increases the loudness of sounds below a threshold while leaving louder passages unchanged. Both downward and upward compression reduce the dynamic range of an audio signal.

Audio tape recorder/player
An audio tape recorder, tape deck or tape machine is an audio storage device that records and plays back sounds, including articulated voices, usually using magnetic tape, either wound on a reel or in a cassette, for storage. In its present-day form, it records a fluctuating signal by moving the tape across a tape head that polarizes the magnetic domains in the tape in proportion to the audio signal. Tape-recording devices include reel-to-reel tape deck and the cassette deck.

DAT (Digital Audio Tape)
Digital Audio Tape (DAT or R-DAT) is a signal recording and playback medium developed by Sony and introduced in 1987. In appearance it is similar to a Compact Cassette, using 3.81 mm / 0.15" (commonly referred to as 4mm) magnetic tape enclosed in a protective shell, but is roughly half the size at 73 mm × 54 mm × 10.5 mm. As the name suggests, the recording is digital rather than analog. DAT has the ability to record at higher, equal or lower sampling rates than a CD (48, 44.1 or 32 kHz sampling rate respectively) at 16 bits quantization. If a digital source is copied then the DAT will produce an exact clone, unlike other digital media such as Digital Compact Cassette or non-Hi-MD Minidisc, both of which use a loss data reduction system.
Like most formats of videocassette, a DAT cassette may only be recorded and played in one direction, unlike an analog compact audio cassette.

Uses of DAT

Professional recording industry

Amateur and home use

Computer data storage medium

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DAT (Digital Audio Tape) is a standard medium and technology for the digital recording of audio on tape at a professional level of quality. A DAT drive is a digital tape recorder with rotating heads similar to those found in a video deck. Most DAT drives can record at sample rates of 44.1 KHz, the CD audio standard, and 48 kHz. DAT has become the standard archiving technology in professional and semi-professional recording environments for master recordings. Digital inputs and outputs on professional DAT decks allow the user to transfer recordings from the DAT tape to an audio workstation for precise editing. The compact size and low cost of the DAT medium makes it an excellent way to compile the recordings that are going to be used to create a CD master.

Optical disc player

An optical disc (OD) is a flat, usually circular disc which encodes binary data (bits) in the form of pits (binary value of 0 or off, due to lack of reflection when read) and lands (binary value of 1 or on, due to a reflection when read) on a special material (often aluminum on one of its flat surfaces.

Optical discs are usually between 7.6 and 30 cm (3 to 12 in) in diameter, with 12 cm (4.75 in) being the most common size. A typical disc is about 1.2 mm (0.05 in) thick, while the track pitch (distance from the center of one track to the center of the next) ranges from 1.6 µm (forCDs) to 320 nm (for Blu-ray discs).
Optical discs are most commonly used for storing music (e.g. for use in a CD player), video (e.g. for use in a Blu-ray player), or data and programs for personal computers (PC).

Video cassette tape recorder/ player
The videocassette recorder,  VCR, or video recorder is an electromechanical device that records analog audio and analog video from broadcast television or other source on a removable, magnetic tape videocassette, and can play back the recording. Use of a VCR to record a television program to play back at a more convenient time is commonly referred to as time shifting. VCRs can also play back prerecorded tapes. In the 1980s and 1990s, until the VCR was superseded by the DVD player and PVR, prerecorded videotapes were widely available for purchase and rental, and blank tapes were sold to make recordings.
Most domestic VCRs are equipped with a television broadcast receiver (tuner) for TV reception, and a programmable clock (timer) for unattended recording of a television channel from a start time to an end time specified by the user. These features began as simple mechanical counter-based single-event timers, but were later replaced by more flexible multiple-event digital clock timers. In later models the multiple timer events could be programmed through a menu interface displayed on the playback TV screen ("on-screen display" or OSD).

A video tape recorder (VTR) is a tape recorder designed to record video material on magnetic tape. The first practical video tape recorder, using transverse tape head scanning, was developed by Ampex Corporation in 1956. The early VTRs were reel to reel devices which recorded on individual reels of 2 inch (5.08 cm) wide magnetic tape. They were used in television studios, serving as a replacement for motion picture film stock and making recording for television applications cheaper and quicker. Beginning in 1963, videotape machines made instant replay during televised sporting events possible. Improved formats, in which the tape was contained inside a videocassette, were introduced around 1969; the machines which play them are called videocassette recorders. Agreement by Japanese manufacturers on a common standard recording format, so cassettes recorded on one manufacturer's machine would play on another's, made a consumer market possible, and the first consumer videocassette recorder was introduced by Sony in 1971.

Video format
A video file format is a type of file format for storing digital video data on a computer system. Video is almost always stored in compressed form to reduce the file size.
A video file normally consists of a container format (e.g. Matroska) containing video data in a video coding format (e.g. VP9) alongside audio data in an audio coding format (e.g. Opus). The container format can also contain synchronization information, subtitles, and metadata such as title etc... A standardized (or in some cases de facto standard) video file type such as .webm is a profile specified by a restriction on which container format and which video and audio compression formats are allowed.
The coded video and audio inside a video file container (i.e. not headers, footers and metadata) is called the essence. A program (or hardware) which can decode video or audio is called a codec; playing or encoding a video file will sometimes require the user to install a codec library corresponding to the type of video and audio coding used in the file.
Good design normally dictates that a file extension enables the user to derive which program will open the file from the file extension. That is the case with some video file formats, such as WebM (.webm), Windows Media Video (.wmv), and Ogg Video (.ogv), each of which can only contain a few well-defined subtypes of video and audio coding formats, making it relatively easy to know which codec will play the file. In contrast to that, some very general-purpose container types like AVI (.avi) and Quicktime (.mov) can contain video and audio in almost any format, and have file extensions named after the container type, making it very hard for the end user to use the file extension to derive which codec or program to use to play the files.

Name	File extension(s)	Container	Video coding format(s)	Audio coding format(s)	Notes
WebM	.webm	Matroska	VP8, VP9	Vorbis, Opus	Free and libre format created for HTML5 video.
Matroska	.mkv	Matroska	Any	Any
Flash Video(FLV)	.flv	FLV	VP6,Sorenson Spark, Screen video, Screen video 2, H.264	MP3, ADPCM,Nellymoser, Speex,AAC	Use of the H.264 and AAC compression formats in the FLV file format has some limitations and authors of Flash Player strongly encourage everyone to embrace the new standard F4V file format.[2] De facto standard for web-based streaming video (over RTMP).
F4V	.flv	MPEG-4 Part 12	H.264	MP3, AAC	Replacement for FLV.
Vob	.vob	VOB	H.262/MPEG-2 Part 2 orMPEG-1 Part 2	PCM, DTS, MPEG-1,Audio Layer II(MP2), or Dolby Digital (AC-3)]	Files in VOB format have .vob filename extension and are typically stored in the VIDEO_TS folder at the root of a DVD.[5] The VOB format is based on the MPEGprogram stream format.
Ogg Video	.ogv, .ogg	Ogg	Theora, Dirac	Vorbis, FLAC	Open source
Dirac	.drc	?	Dirac	?	Open source
GIF	.gif	N/A	N/A	none	Simple animation, inefficient compression, no sound, widely supported

Video camcorders

A video camera is a camera used for electronic motion picture acquisition (as opposed to a movie camera, which records images on film), initially developed for the television industry but now common in other applications as well.
Video cameras are used primarily in two modes. The first, characteristic of much early broadcasting, is live television, where the camera feeds real time images directly to a screen for immediate observation. A few cameras still serve live television production, but most live connections are for security, military/tactical, and industrial operations where surreptitious or remote viewing is required. In the second mode the images are recorded to a storage device for archiving or further processing; for many years, videotape was the primary format used for this purpose, but was gradually supplanted by optical disc, hard disk, and then flash memory. Recorded video is used in television production, and more often surveillance and monitoring tasks in which unattended recording of a situation is required for later analysis.
Modern video cameras have numerous designs and uses.
·         Professional video cameras, such as those used in television production, may be television studio-based or mobile in the case of an electronic field production (EFP). Such cameras generally offer extremely fine-grained manual control for the camera operator, often to the exclusion of automated operation. They usually use three sensors to separately record red, green and blue.
·         Camcorders combine a camera and a VCR or other recording device in one unit; these are mobile, and were widely used for television production, home movies, electronic news gathering (ENG) (including citizen journalism), and similar applications. Since the transition to digital video cameras, most cameras have in-built recording media and as such are also camcorders.
·         Closed-circuit television (CCTV) generally uses pan tilt zoom cameras (PTZ), for security, surveillance, and/or monitoring purposes. Such cameras are designed to be small, easily hidden, and able to operate unattended; those used in industrial or scientific settings are often meant for use in environments that are normally inaccessible or uncomfortable for humans, and are therefore hardened for such hostile environments (e.g. radiation, high heat, or toxic chemical exposure).
·         Webcams are video cameras which stream a live video feed to a computer.
·         Camera phones - nowadays most video cameras are incorporated into mobile phones.
·         Special camera systems are used for scientific research, e.g. on board a satellite or a spaceprobe, in artificial intelligence and robotics research, and in medical use. Such cameras are often tuned for non-visible radiation for infrared (for night vision and heat sensing) or X-ray (for medical and video astronomy use).

Video digitization techniques
Digitization is the process of converting information into a digital format . In this format, information is organized into discrete units of data (called bit s) that can be separately addressed (usually in multiple-bit groups called byte s). This is the binary data that computers and many devices with computing capacity (such as digital camera s and digital hearing aid s) can process.
Digitizing or digitization is the representation of an object,  image, sound, document or signal (usually an analog signal) by generating a series of numbers that describe a discrete set of its points or samples. The result is called digital representation or, more specifically, digital, for the object, and digital form, for the signal. In modern practice, the digitized data is in the form of binary numbers, which facilitate computer processing and other operations, but strictly speaking, digitizing simply means the conversion of analog source material into a numerical format; the decimal or any other number system can be used instead.
Digitization is of crucial importance to data processing, storage and transmission, because it "allows information of all kinds in all formats to be carried with the same efficiency and also intermingled".[2] Unlike analog data, which typically suffers some loss of quality each time it is copied or transmitted, digital data can, in theory, be propagated indefinitely with absolutely no degradation.
Digitization occurs in two parts:
Discretization
The reading of an analog signal A, and, at regular time intervals (frequency), sampling the value of the signal at the point. Each such reading is called a sample and may be considered to have infinite precision at this stage.
Quantization
Samples are rounded to a fixed set of numbers (such as integers), a process known as quantization.
Video optical discs (DVD):

DVD is an optical disc technology with a 4.7 gigabyte storage capacity on a single-sided, one-layered disk, which is enough for a 133-minute movie. DVDs can be single- or double-sided, and can have two layers on each side; a double-sided, two-layered DVD will hold up to 17 gigabytes of video, audio, or other information. This compares to 650 megabytes (.65 gigabyte) of storage for a CD-ROM disk.

DVD uses the MPEG-2 file and compression standard. MPEG-2 images have four times the resolution of MPEG-1 images and can be delivered at 60 interlaced fields per second where two fields constitute one image frame. (MPEG-1 can deliver 30 no interlaced frames per second.) Audio quality on DVD is comparable to that of current audio compact discs.

Formats:

·         DVD-Video is the format designed for full-length movies that work with your television set.

·         DVD-ROM is the type of drive and disc for use on computers. The DVD drive will usually also play regular CD-ROM discs and DVD-Video disks.

·         DVD-RAM is the writeable version.

·         DVD-Audio is a CD-replacement format.

·         There are a number of recordable DVD formats, including DVD-R for General, DVD-R for Authoring, DVD-RAM, DVD-RW, DVD+RW, and DVD+R.

DVD was originally said to stand for digital video disc, and later for digital versatile disc. The current official stance of the DVD Forum is that the format should just be referred to as DVD

Hi-Fi audio amplifiers

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Audio recording systems

Analog (or analogue) recording (Greek, ana is "according to" and logos "relationship") is a technique used for the recording of analog signals which, among many possibilities, allows analog audio and analog video for later playback.

Analog recording methods store signals as a continuous signal in or on the media. The signal may be stored as a physical texture on a phonograph record, or a fluctuation in the field of a magnetic recording. This is different from digital recording which digital signals are represented as discrete numbers.

A Digital Recording/Processing System

A block diagram of a digital recording/processing system is shown in figure 2. The processes at each of the numbered blocks 1 to 7 are described below:

Figure 2: Block diagram of digital recording processing system. Both sources of noise [N₁ (t), N₂ (t)] are needed in order to avoid digital distortions of the signal V (t) in the form of coherent noise N_D (t). Properly chosen N₁ (t) and N₂ (t) add only a little noise to the output, but remove coherence of N_D (t) (digital noise) with the signal V (t).

1.      Following Nakajima (1983), Mieszkowski (1989) and Wannamaker, Lipshitz and Vanderkooy (1989), analog dither must be added to the input signal in order to

a) Linearize the A/D converter

b) Make possible improvement of S/N by averaging process according to formula:

(S/N) after averaging = (S/N) before averaging  n1/2

(5)

Where: n = No. of averaged signals

c) Eliminate harmonic distortions (created when digital noise N_D (t) is coherent with signal V (t)).

d) Eliminate intermodulation distortion (created as well when digital noise N_D (t) is coherent with signal V (t)).

e) eliminate "digital deafness" (when the signal V(t) falls below  , where   is the step size in the A/D converter, the signal will not be recorded at all unless there is a noise N₁(t) on the input).

f) Eliminate noise modulation by the signal

2.      Input low pass filter (antialiasing filter) should eliminate all frequencies above f_ess / 2 , where f_s= sampling frequency, in order to avoid aliasing distortion (Folding of frequencies into passband: f_new = f_s - f_original where f_original   f_s / 2).

3.      A/D converter converts analog signal into a digital number (for example, 10110110 represents a binary coded 8-bit amplitude). Sampling speeds range from 2 kHz to 10 GHz and amplitude resolution ranges from 4 bits to 20 bits.

4.      If DSP is performed on the signal, one must add digital dither N₂(t) (box 5) to avoid digital distortions and coherent noise N_D (t) on the output of D/A converter. Digital processing should also be performed using sufficiently precise real numbers to avoid round-off errors.

Storage of digital data can be performed on magnetic tape, optical disk, magnetic disk, or RAM (Random Access Memory). Prior to storage, extra code is generated to allow for error correction. This error correction code allows detection and correction of errors during playback of the audio signal. Redundant information must be added to the original signal in order to combat noise inherent in any storage/communication system. The particular type of code and error correction system depends on storage medium, communication channel used and immunity from errors (an arbitrarily small probability of error can be obtained, Nakajima, 1983; Shannon, 1949/1975).

5.      Prior to D/A conversion, digital dither must be added to numbers representing amplitude of the signal if DSP has been performed. Optimal digital dither has triangular probability density function (PDF) (Wannamaker, et al. 1989).

6.      D/A converter converts digital numbers into analog signal. Available conversion speeds are 2 kHz to 200 MHz and available amplitude resolution is 4 bits to 20 bits.

7.      Output low pass filter should eliminate all frequencies above f_s /2 which are generated during D/A conversion.

Video camera

A video camera is a camera used for electronic motion picture acquisition (as opposed to a movie camera, which records images on film), initially developed for the television industry but now common in other applications as well.

Modern video cameras have numerous designs and uses.

·         Professional video cameras, such as those used in television production, may be television studio-based or mobile in the case of an electronic field production (EFP). Such cameras generally offer extremely fine-grained manual control for the camera operator, often to the exclusion of automated operation. They usually use three sensors to separately record red, green and blue.

·         Camcorders combine a camera and a VCR or other recording device in one unit; these are mobile, and were widely used for television production, home movies, electronic news gathering (ENG) (including citizen journalism), and similar applications. Since the transition to digital video cameras, most cameras have in-built recording media and as such are also camcorders.

·         Closed-circuit television (CCTV) generally uses pan tilt zoom cameras (PTZ), for security, surveillance, and/or monitoring purposes. Such cameras are designed to be small, easily hidden, and able to operate unattended; those used in industrial or scientific settings are often meant for use in environments that are normally inaccessible or uncomfortable for humans, and are therefore hardened for such hostile environments (e.g. radiation, high heat, or toxic chemical exposure).

·         Webcams are video cameras which stream a live video feed to a computer.

·         Camera phones - nowadays most video cameras are incorporated into mobile phones.

·         Special camera systems are used for scientific research, e.g. on board a satellite or a space probe, in artificial intelligence and robotics research, and in medical use. Such cameras are often tuned for non-visible radiation for infrared (for night vision and heat sensing) or X-ray (for medical and video astronomy use).

·          

Video recording systems

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Digital video is a representation of moving visual images in the form of encoded digital data. This is in contrast to analog video, which represents moving visual images with analog signals.

Basic TV broadcasting techniques

The various methods of TV transmission

Programming broadcast is the transmission of television stations’ programming (sometimes called channels) that is often directed to a specific audience.

There are several types of TV broadcast systems:

§  Analogue Terrestrial TV

§  Systems for sound transmission

§  Digital Satellite TV

§  Cable TV: analogue and digital systems

§  New technologies:

§  Digital terrestrial TV (DTTV)

§  High Definition Television (HDTV)

§  Pay-per-view

§  Video-on-demand

§  Web TV

§  IPTV

The various methods of TV transmission

Programming broadcast is the transmission of television stations’ programming (sometimes called channels) that is often directed to a specific audience.

There are several types of TV broadcast systems:

§  Analogue Terrestrial TV

§  Systems for sound transmission

§  Digital Satellite TV

§  Cable TV: analogue and digital systems

§  New technologies:

§  Digital terrestrial TV (DTTV)

§  High Definition Television (HDTV)

§  Pay-per-view

§  Video-on-demand

§  Web TV

§  IPTV

ANALOGUE TERRESTRIAL TV

Terrestrial television is a term which refers to modes of television broadcasting which do not involve satellite transmission or via underground cables.

Terrestrial television broadcasting dates back to the very beginnings of television as a medium itself and there was virtually no other method of television delivery until the 1950s with the beginnings of cable television, or community antenna television (CATV).

The first non-terrestrial method of delivering television signals that in no way depended on a signal originating from a traditional terrestrial source began with the use of communications satellites during the 1960s and 1970s of the twentieth century.

Analogue TV encodes the image and sound information and transmits them as an analogue signal in which the message transmitted by the broadcasting signal is composed of amplitude and/or frequency variations and modulated into a VHF or UHF carrier.

The analogue television picture is "drawn" several times on the screen (25 in PAL system) as a whole each time, as in a motion picture film, regardless of the content of the image.

DIGITAL SATELLITE TV

Satellite television is television signals delivered by means of communications satellites and received by satellite dishes and set-top boxes. In many areas of the world it provides a wide range of channels and services, often to areas that are not serviced by terrestrial or cable providers.

Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility which have very large uplink satellite dishes, as much as 9 to 12 meters (30 to 40 feet) in diameter what results in more accurate aiming and increased signal strength at the satellite.

The uplink dish is pointed toward a specific satellite and the uplinked signals are transmitted within a specific frequency range, so as to be received by one of the transponders tuned to that frequency range aboard that satellite, which 'retransmits' the signals back to Earth but at a different frequency band, a process known as “translation”, used to avoid interference with the uplink signal, typically in the C-band (4–8 GHz) or Ku-band (12–18 GHz) or both.

CABLE TV

Cable Television or Community Antenna Television (CATV) is a system for distribution of audiovisual content for television, FM radio and other services to consumers through fixed coaxial cables, avoiding the traditional system of radio broadcasting antennas (broadcast television) and have widespread use, mainly through the pay-tv services.

Technically, the cable TV involves the distribution of a number of television channels received and processed in a central location (known as head-end) to subscribers within a community through a network of optical fiber and/or coaxial cables and broadband amplifiers.

The use of different frequencies allows many channels to be distributed through the same cable, without separate wires for each, and the tuner of the TV or Radio selects the desired channel from among all transmitted.

A cable television system begins at the head end, where the program is received (and sometimes originated), amplified, and then transmitted over a coaxial cable network.

The architecture of the network takes the form of a tree, with the "trunk" that carries the signals in the streets, the "branches" carrying the signals for buildings and, finally, the "arms" carrying the signals to individual homes.

The coaxial cable has a bandwidth capable of carrying a hundred television channels with six megahertz of bandwidth each, but the signals decay quickly with distance, hence the need to use amplifiers to "renew" the signals periodically to boost them.

Backbone trunks in a local cable network frequently use optical fiber to minimize noise and eliminate the need for amplifiers as optical fiber has considerably more capacity than coaxial cable and allows more programs to be carried without signal lost or noise adding.

Most of the TV tuners are able to directly receive the cable channels, which are usually transmitted in the RF (radio frequency) band, however, many programs are encrypted and subject to a tariff itself and in such cases, you must install a converter between the cable and the receiver.

DIGITAL TERRESTRIAL TV

Digital Terrestrial Television (DTTV or DTT) is an implementation of digital television technology to provide a greater number of channels and/or better quality of picture and sound using aerial broadcasts to a conventional antenna (or aerial) instead of a satellite dish or cable connection.

The technology used in Europe is DVB-T that is immune to multipath distortion.

DTTV is transmitted on radio frequencies through the airwaves that are similar to standard analogue television, with the primary difference being the use of multiplex transmitters to allow reception of multiple channels on a single frequency range (such as a UHF or VHF channel).

The amount of data that can be transmitted (and therefore the number of channels) is directly affected by the modulation method of the channel.

The modulation method in DVB-T is COFDM with either 64 or 16 state Quadrature Amplitude Modulation (QAM). In general a 64QAM channel is capable of transmitting a greater bit rate, but is more susceptible to interference. 16 and 64QAM can be combined in a single multiplex, providing a controllable degradation for more important programmer streams. This is called hierarchical modulation.

New developments in compression have resulted in the MPEG-4/AVC standard which will enable two high definition services to be coded into a 24 Mbit/s European terrestrial transmission channel.

DTTV is received via a digital set-top box, or integrated receiving device, that decodes the signal received via a standard aerial antenna, however, due to frequency planning issues, an aerial with a different group (usually a wideband) may be required if the DTTV multiplexes lie outside the bandwidth of the originally installed aerial.

In Portugal, as detailed in the information published by ANACOM in February 2008, Set Top Boxes (STB) or TV receivers must be capable of decoding MPEG-4, H.264 AVC coded transmissions and also be suitable to display HD signals in at least 720p format, as this is the format to be broadcast on the country.

In the case of STB’s, ANACOM advises that an HDMI connection should also be available and that it should be version 1.3 and that the box should of course decode the transmitted HDTV format.

HDTV

The high-definition television, also known as HDTV (High Definition Television) is a television system with a resolution significantly higher than in the traditional formats (NTSC, SECAM, PAL).

The HDTV is transmitted digitally and therefore its implementation generally coincides with the introduction of digital television (DTV), technology that was launched during the 1990s.

Although several patterns of high-definition television have been proposed or implemented, the current HDTV standards are defined by ITU-R BT.709 as 1080i (interlaced), 1080p (progressive) or 720p using the 16:9 screen format.

The term "high definition" can refer to the specification of the resolution itself or, more generally, the media capable of such a definition as the video media support or the television set.

What will be of interest in the near future is high definition video, through the successors of the DVD, HD DVD and Blu-Ray (is expected that the last one will be adopted as a standard) and, consequently, the projectors and LCD and plasma televisions sets as well as retro projectors and video recorders with 1080p resolution/definition.

High-definition television (HDTV) yields a better-quality image than standard television does, because it has a greater number of line resolution.

The visual information is some 2 to 5 times sharper because the gaps between the scan lines are narrower or invisible to the naked eye.

The larger the size of the television the HD picture is viewed on, the greater the improvement in picture quality. On smaller televisions there may be no noticeable improvement in picture quality.

The lower-case "I" appended to the numbers denotes interlaced; the lower-case "p" denotes progressive: With the interlaced scanning method, the 1,080 lines of resolution are divided into pairs, the first 540 alternate lines are painted on a frame and then the second 540 lines are painted on a second frame; the progressive scanning method simultaneously displays all 1,080 lines on every frame, requiring a greater bandwidth.

PAY-PER-VIEW

Pay-per-view (often abbreviated PPV) offers a system by which a television audience can purchase events to view on TV-monitors via private telecast of that event to their homes.

The broadcaster shows the event at the same time to everyone ordering it (as opposed to video-on-demand systems, which allow viewers to see the event at any time) and can be purchased using an on-screen guide, an automated telephone system, or through a live customer service representative.

Events often include feature films, sporting events, adult content movies and "special" events.

VIDEO-ON-DEMAND

Video-on-Demand (VoD) or Audio-Video-on-Demand (AVoD) systems allow users to select and watch/listen to video or audio content on demand.

VoD systems either stream content through a set-top-box, allowing viewing in real time, or download it to a device such as a computer, digital video recorder, personal video recorder or portable media player for viewing at any time.

Download and streaming video-on-demand systems provide the user with a large subset of VCR functionality including pause, fast forward, fast rewind, slow forward, slow rewind, jump to previous/future frame etc., these functions are called trick modes.

For disk-based streaming systems which store and stream programs from hard disk drive, trick modes require additional processing and storage on the part of the server, because separate files for fast forward and rewind must be stored.

Memory-based VoD streaming systems have the advantage of being able to perform trick modes directly from RAM, which requires no additional storage or CPU cycles on the part of the processor.

It is possible to put video servers on LANs, in which case they can provide very rapid response to users. Streaming video servers can also serve a wider community via a WAN, in which case the responsiveness may be reduced. Download VoD services are practical to homes equipped with cable modems or DSL connections.

WEB TV

Web TV, TVIP, or TV on the Internet is the transmission of a programming grid through the Internet. It can be known "normal" TV channels or channels specifically designed for the Internet.

Web TV, in a simplified form, is nothing more than the provision of video and audio over the Internet; and the way to assist the transmission varies from the monitor of a computer through the use of an iPod or a mobile phone to the TV set if one have the decoder.

IPTV (TV over Internet Protocol)

The recent introduction of Television over Internet Protocol technology, commonly known as IPTV, made a revolution on the distribution networks for TV signals, allowing eliminate many of the problems associated with a distribution network based on coaxial cables, in particular those related with the degradation of signal, interference, signal levels, and capacity of the transmission of the channel’s band.

Moreover, thanks to IP (Internet Protocol), will be possible the combination of several interfaces in a multi-service unit and the broadcast and distribution of diverse and varied services on the same network, which previously required differentiated infrastructure, including: TV signals, telephone service and broadband Internet access, setting a platform we know today as Triple Play.

In essence, the triple play concept is not entirely new because, in terms of services, there are some years ago that are available some solutions combining a mix of TV services, telephony and Internet access.

Studies show that the churn rate (voluntary abandonment of service) of the offer triple play subscribers is substantially lower than that observed when the voice, data and TV are sold on a non-convergent way.

Another factor is the progress in access technologies and platforms for packet telephony and video. A variant of ADSL (asymmetrical digital subscriber line), known as ADSL2+, represents a change in the effective performance of Internet connection on the original format, not to mention the more recent developments, such as VDSL (very-high-bit-rate DSL).

The access over optical fiber in its more popular form, known as PON (passive optical network), reflects an even more daring way, resulted in significant investments in that technology, seeking for high-speed Internet access, voice and multi-channel of high-definition TV union.

Progress in video distribution systems is on the way too. In recent years, a number of innovations and developments in the industry of hardware and software systems for the TV industry have started to TV over IP (also known as IPTV).

The main driver is integrated platforms consisting of set-top-boxes, servers and video content protection system (DRM - digital rights management), together with appropriate tools, middleware and billing, allow the provision of a variety of TV services in several formats, such as streaming, video on demand and time-shifted TV, based on a combination of underlying IP networks and DSL or optical access systems.

In this context, the sophistication of algorithms for compression of video signals has a relevant role. Techniques such as MPEG-4 AVC (advanced video coding), for example, enable the transmission of signals in high definition TV over IP networks.

The search for a strategy to offer multiple play-based (dual, triple, quadruple etc.) is an irreversible phenomenon in the communications industry but at the same time it impose enormous challenges - particularly in terms of selection of technology platforms, control and regulation - opens a huge horizon of possibilities, both supply and demand.

Mono sound reception:

Mono or monophonic describes a system where all the audio signals are mixed together and routed through a single audio channel. Mono systems can have multiple loudspeakers, and even multiple widely separated loudspeakers. The key is that the signal contains no level and arrival time/phase information that would replicate or simulate directional cues. Common types of mono systems include single channel center clusters, mono split cluster systems, and distributed loudspeaker systems with and without architectural delays. Mono systems can still be full-bandwidth and full-fidelity and are able to reinforce both voice and music effectively. The big advantage to mono is that everyone hears the very same signal, and, in properly designed systems, all listeners would hear the system at essentially the same sound level. This makes well-designed mono systems very well suited for speech reinforcement as they can provide excellent speech intelligibility.

Stereo Sound reception

True stereophonic sound systems have two independent audio signal channels, and the signals that are reproduced have a specific level and phase relationship to each other so that when played back through a suitable reproduction system, there will be an apparent image of the original sound source. Stereo would be a requirement if there is a need to replicate the aural perspective and localization of instruments on a stage or platform, a very common requirement in performing arts centers.

This also means that a mono signal that is panned somewhere between the two channels does not have the requisite phase information to be a true stereophonic signal, although there can be a level difference between the two channels that simulates a position difference, this is a simulation only. That's a discussion that could warrant a couple of web pages all by itself.

An additional requirement of the stereo playback system is that the entire listening area must have equal coverage of both the left and right channels, at essentially equal levels. This is why your home stereo system has a "sweet spot" between the two loudspeakers, where the level differences and arrival time differences are small enough that the stereo image and localization are both maintained. This sweet spot is limited to a fairly small area between the two loudspeakers and when a listener is outside that area, the image collapses and only one or the other channel is heard. Living with this sweet spot in your living room may be OK, since you can put your couch there, but in a larger venue, like a church sanctuary or theatre auditorium, that sweet spot might only include 1/3 the audience, leaving 2/3 of the audience wondering why they only hear half the program.

HI-FI Audio:

a.Streaming

b. Headphones

c. Wires & cables

d. Speakers

e. Stereo amplifier & receivers

f. Turntable & cartridges