Audio Glossary

February 15, in Features

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #

Select the first letter of the word from the list above to jump to appropriate section of the glossary. If the term you are looking for starts with a digit or symbol, choose the ‘#’ link.


– A –

AAC (Advanced Audio Coding)

AAC is the audio coding standard defined by the International Organization for Standardization (ISO) as part of the MPEG-2 specification. Declared an international standard in April 1997, MPEG-2 AAC builds upon and extends the popular ISO/MPEG-1 Audio Layer-3 (MP3) audio coding format. Compared to MP3, AAC provides higher quality music with approximately 30% storage space or bandwidth. AAC provides up to 48 audio channels and sample rates up to 96 kHz.,

AC-3

See “Dolby Digital”

AES/EBU

Audio Engineering Society / European Broadcast Union is a digital audio standard commonly used in linking professional digital audio equipment. The AES/EBU digital interface is usually implemented using 3-pin XLR connectors, the same type connector used in a professional microphone. One cable carries both right and left channels. AES/EBU is an alternative to the S/PDIF standard.

ampere (A)

The unit of measurement for electrical current in coulombs per second. There is one ampere in a circuit that has one ohm resistance when one volt is applied to the circuit. See Ohms Law

amplifier (amp)

A device that increases signal level. Many types of amplifiers are used in audio systems. A pre-amplifier is used to increase the signal level from an audio source. A power amplifier increases the signal level sufficiently to drive a speaker. Pre-amplifiers and power amplifiers can be purchased as separate units or can be packaged together with other audio functions. A receiver is an audio unit that contains pre-amplifier, control, switching, processing, and power amplifier functions built into a single unit.
Audio power amplifiers are primarily classified by their design. Various classes of audio power amplifiers are:

  • Class A

  • Class B

  • Class AB

  • Class AB plus B

  • Class D

  • Class G

  • Class H

analog

The method of representing and storing audio information with continuously variable physical quantities. Audio in an analog signal is represented by the varying of a voltages speed (frequency) and strength (amplitude) to correspond to how the audio changes in frequency and volume. Contrasted with digital

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– B –

bit

Originally short for “Binary Digit”. In digital, the small unit of information. A bit represents either an “on” of “off” value represented by a “0” or “1”.

bit stream

Refers to a stream of bits transmitted over a communications line between two devices.


byte

A unit of digital value the consists of 8 bits. Computer memory or storage is usually in the number of bytes such as kilobytes, megabytes, and gigabytes.

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– C –

CD

“Compact Disk” An optical disk storage media that is designed to store audio, video, and computer data in a digital format. CD’s have a capacity to store 650 Mb (megabytes) of data. The digital information in a standard audio CD is encoded in the PCM format.

compression

To reduce in size. Various methods encoding digital information can be used to reduce the size of an original digital recording by eliminating redundant information or information that is viewed as unnecessary or not critical. PCM is not a compressed digital format. Various common encoding methods and their compression ratios compared to PCM are Dolby Digital (12:1) and DTS (3:1)

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– D –

DAC

A digital to analog converter. Converts a digital bitstream to an analog signal. Can be a separate “unit” that connects between a CD Player and a pre-amplifier.

DAB

See “Digital Audio Broadcasting

dB

An abbreviation for decibel.

decibel (dB)

A scale to measure the loudness of sound. A difference of 1 dB is usually the minimum perceptible change in volume, 3 dB is a moderate change in volume, and 10 dB is an apparent doubling of volume. Decibels are a logarithmic scale of relative loudness. In audio equipment decibels are used to indicate the range of volume from the quietest to the loudest sound that can be handled. The volume of common sounds in decibels are:

  • 0 dB is the threshold of hearing, 130 dB is the threshold of pain

  • Whisper: 15 – 25 dB

  • Quite background: about 35 dB

  • Normal home or office background: 40 – 60 dB

  • Normal speaking voice: 65 – 70 dB

  • Orchestral climax: 105 dB

  • Live rock music: 120 dB+

  • Jet aircraft: 140 – 180 dB


digital

The method of representing and storing audio information with numbers. Audio in a digital signal can be represented by many different schemes. One common scheme is PCM. Contrasted with analog.


dither

The method used in digital systems to smooth out the transitions from one bit to another at low levels. Dither makes a digital recording sound and behave more like analog. The better a recording is dithered, the higher its apparent resolution.


Digital Audio Broadcasting (DAB)

Also know as digital radio, Digital Audio Broadcasting is a digital method of transmitting audio and other information over the airways to radio receivers. In the United States a technology has been proposed called IBOC that uses the existing AM and FM frequency bands assigned to radio stations.


Dolby Digital

A 5.1 multi-channel surround format consisting of discreet front left, front center, front right, rear left, rear right, and a low-frequency-effects (LFE) channel. Dolby Digital is compressed approximately 12:1 compared to PCM.


Dolby Digital Surround EX

An enhancement to the Dolby Digital 5.1 where a rear center channel has been added creating a 6.1 format. The Dolby Digital Surround EX format does not add an additional discreet recorded channel. The new rear center or “back” channel is matrix-encoded in the Dolby Digital left and right surround signals. The recorded Dolby Digital audio consists of five discrete main channels and a sixth, low-frequency-effects (LFE) channel. The two rear surround channels carry the signal for the rear center or “back” channel. The Dolby Digital Surround EX format made is debut in the 1999 movie Star Wars: Episode I – The Phantom Menace.


DSD

“Direct Stream Digital”. A digital encoding format proposed by Sony and Philips used to record SACD albums. DSD samples an audio signal at a fixed rate (frequency) just as in the PCM method. However, instead of recording the volume or amplitude as an absolute number, as in PCM, the DSD method measures and records how much the volume has changed since the last measurement. If the signal is sampled fast enough, the amount of change since the previous sample would be very small. The proposal for DSD is for a sampling rate that’s over 2 MHz (2 million times per second)! At this high speed the changes in signal strength can be represented with one bit. DSD also compresses the data resulting in a 2:1 reduction.. DSD will be able to provide a frequency response from DC to 100 kHz with a dynamic range of 120 dB.


DSB

“direct-broadcast-satellite”


DTS

“Digital Theater Systems” – a multi-channel (5.1) digital audio encoding format created by Digital Theater Systems. The DTS format was introduced in theaters in 1993, with Steven Spielberg’s blockbuster movie Jurassic Park. In addition, the DTS format has been applied to home CD’s, Laser Disks, and DVD’s. DTS audio, as used in DVD-Video’s and CD’s, is compressed approximately 3:1 from PCM recorded with a sampling frequency of 96 kHz and a 20-bit sampling size. DTS is capable of encoding PCM with a sampling frequency up to 192 kHz and 24-bit sampling size.


DTV

“Digital Television”


DVD

Digital Video Disk or Digital Versatile Disk. An optical disk storage media that can store video, audio, and computer data. There are multiple standards and formats for DVD’s. However, typically a DVD-Video is referred to as a DVD. Various DVD formats are:

DVD-Audio

DVD-R

DVD-ROM

DVD-RW

DVD-Video

DVD+RW

DVD-Audio

An audio standard for high quality audio recorded on DVD’s that exceed the capacity and quality of CD’s. An DVD-Audio disk is capable of recording audio with frequencies up to 96Khz (compared to CD’s at 20kHz) and with a dynamic range of up to 144dB (compared to CD’s 96dB). DVD-Audio supports multi-channel recordings.

DVD-RAM

A rewritable DVD format.

DVD-ROM

A DVD that stores computer data and is read by a DVD-ROM drive attached to a computer. A DVD-ROM is a “read only memory” media. DVD-ROM also includes recordable variations (DVD-R, DVD-RW, and DVD+RW)

DVD-Video

Commonly referred to as a DVD. A DVD-Video stores video and audio information that is played by a DVD-Video player attached to a TV.


dynamic range

The range between the loudest and the softest sounds that are in a piece of music or that can be reproduced by a piece of audio equipment without distortion. This is a ratio expressed in decibels (dB). In speech the range rarely exceeds 40 dB; in music the range can reach over 75 dB.

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– E –

EDTV

See “Enhanced Definition Television


Enhanced Definition Television (EDTV)
:
EDTV refers to a complete product/system with the following minimum performance attributes:

  • Receiver: Receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats
  • Display Scanning Format: Has active vertical scanning lines of 480 progressive (480p) or higher
  • Aspect Ratio: None Specified
  • Audio: Receives and reproduces, and/or outputs Dolby Digital audio


Enhanced Definition Television (EDTV) Monitor
:
EDTV Monitor refers to a monitor or display with the following minimum performance attributes:

  • Display Scanning Format: Has active vertical scanning lines of 480 progressive (480p) or higher
  • Aspect Ratio: None specified


Enhanced Definition Television (EDTV) Tuner
:
EDTV Tuner refers to a RF receiver with the following minimum performance attributes:

  • Receiver: Receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats
  • Outputs: Outputs the ATSC Table 3 720p and 1080i/p and 480p formats with minimum active vertical scanning lines of 480p. Alternatively, the output can be a digital bitstream output capable of transporting 480p, except the ATSC Table 3 480i format can be output at 480i.
  • Audio: Receives and reproduces, and/or outputs Dolby Digital audio

 

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– F –

FireWire

FireWire is the popular name for a high-speed digital standard for connecting peripherals such as digital video cameras, audio components and computer devices. FireWire was originally developed by Apple Computer as a replacement for the SCSI bus. IEEE 1394 is formal name for the standard. Vendors must obtain a license from Apple to use the term FireWire.

frequency

The measurement of the number of cycles per second in an audio tone or an alternating current. Frequency is represented in cycles per second also known as Hertz, abbreviated as Hz. The range of human hearing is typically considered to range from 20Hz to 20,000Hz. (20Hz – 20kHz)

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– G –

Gigabyte (G byte)

One billion bytes. Written as 1Gb. Megabytes are used as a measure of digital storage space.

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– H –

HDTV

See “High-Definition Television


Hertz

A measurement of frequency. One Hertz is equal to one complete cycle per second. Hertz is abbreviated as Hz.


Hexadecimal

A method of representing digital values that are in units of 4 bits or 1/2 of a byte
The values are normally represented as:
Binary Hexadecimal Decimal
00000000 00 0
00000001 01 1
00000010 02 2
00000011 03 3
00000100 04 4
00000101 05 5
00000110 06 6
00000111 07 7
00001000 08 8
00001001 09 9
00001010 0A 10
00001011 0B 11
00001100 0C 12
00001101 0D 13
00001110 0E 14
00001111 0F 15
00010000 10 16
00010001 11 17
00010010 12 18

——————-through—————

11111111 FF 255


High-Definition Television (HDTV):
HDTV refers to a complete product/system with the following minimum performance attributes:

  • Receiver: Receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats
  • Display Scanning Format: Has active vertical scanning lines of 720 progressive (720p), 1080 interlaced (1080i), or higher
  • Aspect Ratio: Capable of displaying a 16:9 image1
  • Audio: Receives and reproduces, and/or outputs Dolby Digital audio


High-Definition Television (HDTV) Monitor:
HDTV Monitor refers to a monitor or display with the following minimum performance attributes:

  • Display Scanning Format: Has active vertical scanning lines of 720 progressive (720p), 1080 interlaced (1080i), or higher
  • Aspect Ratio: Capable of displaying a 16:9 image.
    In specifications found on product literature and in owner’s manuals, manufacturers are required to disclose the number of vertical scanning lines in the 16:9 viewable area, which must be 540p, 810i or higher to meet the definition of HDTV.


High Definition Television (HDTV) Tuner:
HDTV Tuner refers to a RF receiver with the following minimum performance attributes:

  • Receiver: Receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats
  • Outputs: Outputs the ATSC Table 3 720p and 1080i/p formats in the form of HD with minimum active vertical scanning lines of 720p, 1080i, or higher. Additionally, it may output HD formats converted to other formats. The lower resolution ATSC Table 3 formats can be output at lower resolution levels. Alternatively, the output can be a digital bitstream with the full resolution of the broadcast signal.
  • Audio: Receives and reproduces, and/or outputs Dolby Digital audio


Hz

An abbreviation for Hertz.

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– I –

IBOC

“In-Band On-Channel” – A proposed technology for digital radio in the United States. Digital radio is also being referred to as “Digital Audio Broadcasting” or DAB. IBOC allows digital information to be transmitted simultaneously with existing analog broadcast in the same frequency bands that are currently assigned to AM and FM broadcast stations.

IEEE 1394

See FireWire

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– J –

(empty)

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– K –

kilobyte (K byte)

1 K byte is 1,024 bytes or approximately 1,000 bytes. .

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– L –

(empty)

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– M –

megabyte (M byte)

One million bytes. Written as 1Mb. Megabytes are used as a measure of digital storage space. For example, a CD can hold 650Mb.


MP3 (MPEG-1 Audio Layer 3)

MP3 is the audio coding format defined by the International Organization for Standardization (ISO) as part of the MPEG-1 Audio Layer-3 specification. MP3 has become a popular audio compression format on the Internet and computers.

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– N –

(empty)

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– O –

ohm

A unit of electrical resistance or impedance


Ohms Law

A basic law of electrical circuits. The current in amperes (I) in a circuit equal to the voltage (E) in volts divided by the resistance (R) in ohms; I=E/R


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– P –

PCM

“Pulse Code Modulation”. A method of encoding audio information in a digital format. PCM samples analog audio information at a fixed sampling rate and measures the amplitude (volume) of the audio signal with a precision determined by the sampling size. Audio is encoded on CD’s in the PCM format with a sampling frequency of 44.1 kHz and a 16-bit sampling size. A 16-bit sample size can contain 65,536 possible levels of sound volume which corresponds to a dynamic range of 96dB. A DVD-Audio can be encoded in PCM with a sampling frequency of up to 192 kHz and a 24-bit sample size.

perceptual coding

“Perceptual coding” is is a method of audio compression that removes portions of the audio signal that can not be easily perceived by the human ear. Forms of ”perceptual coding” in popular audio coding formats such as Dolby Digital, DTS, MP3 and AAC.

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– Q –

(empty)

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– R –

(empty)

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– S –

SACD

See “Super Audio CD

SDDS

Sony Dynamic Digital Sound” – a multi-channel (5.1 or 7.1) digital format developed by Sony for theatrical film.

SDTV

See “Standard Definition Television

S/PDIF

Sony/Philips Digital Interface Format” – a format for linking consumer digital audio equipment together based upon the AES/EBU standard. S/PDIF typically uses unbalanced high impedance coaxial cables or fiber optical cables; however, high quality audio cables can be used for short lengths. Good 75-ohm cable and good 75-ohm connectors can provide lengths up to 25 feet.


Standard Definition Television (SDTV):
SDTV refers to a complete product/system with the following performance attributes:

  • Receiver: Receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats, and produces a useable picture
  • Display Scanning Format: Has active vertical scanning lines less than that of EDTV
  • Aspect Ratio: None specified
  • Audio: Receives and reproduces usable audio


Standard Definition Television (SDTV) Tuner
:
SDTV Tuner refers to a RF receiver with the following minimum performance attributes:

  • Receiver: Receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats
  • Outputs: Outputs all ATSC table 3 formats in the form of NTSC output
  • Audio: Receives and reproduces, and/or outputs Dolby Digital audio


Super Audio CD (SACD)

Super Audio CD (SACD) is a technology for high resolution multi-channel digital audio recordings proposed by Sony and Philips. SACD albums must contain one layer with the DSD digital encoding format which requires a SACD capable player. SACD albums can optionally contain a second layer encoded with the CD-format (PCM at 44.1-kHz/16-bit) in stereo allowing compatibility with existing CD players.


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– T –

THX®

“Tomlinson Holman Experiment” – processing specifications for audio components (i.e. amplifiers, processors, speakers, etc) for both home and theatre established by Lucasfilm. THX® specifications are designed to provide consistent audio reproduction as close as possible to what was originally intended. Professional and home audio equipment can carry the THX® logo after obtaining THX® certification from Lucasfilm.


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– U –

ultrasonic

A frequency higher than can be heard by the human ear. Usually higher than 20kHz.

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– V –

(empty)

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– W –

watt


A unit of electrical power. The audio power of an amplifier is measured in watts.

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– X –

(empty)

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– Y –

(empty)

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– Z –

(empty)

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– # –

5.1

Multi-channel surround consisting of a front center, front right, front left, rear right, and a rear left channel. The .1 channel is a low-frequency-effects (LFE) sub-woofer channel.


6.1

Multi-channel surround consisting of a front center, front right, front left, rear right, rear left, and a rear center or “back” channel. The .1 channel is a low-frequency-effects (LFE) sub-woofer channel.


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