Digital Audio Final Terms

AC3 Dolby Digital

Active sensing A method by which a MIDI device detects disconnection. A message is sent to the receiver around three times per second and if no message is received during this period the unit assumes the MIDI connection has been broken. It then begins a routine to re-establish normal operation. Not all MIDI devices support active sensing.

ADSR Attack, Decay, Sustain and Release are the four stages of an envelope that describe the shape of a sound over time. This is a simple type of envelope generator and was first used on early analog synthesisers. This form of envelope generator continues to be popular on modern instruments. Attack represents the time the sound takes to rise from an initial value of zero to its maximum level. Decay is the time for the initial falling off to the sustain level. Sustain is the time during which it remains at this level. Release is the time it takes to move from the sustain to its final level. Release typically begins when a note is let up. In most sound generators, the time and the value reached are programmable.

Aftertouch A means of generating a control signal based on how much pressure is applied to the keys of a MIDI keyboard. Most instruments that support this do not have independent pressure sensing for all keys, but rather detect the overall pressure by means of a sensing strip running beneath the keys. Aftertouch may be used to control such functions as vibrato depth, filter brightness, loudness and so on.

AIFF The standard file format for storing audio information on an Apple Macintosh computer.

Algorithm A set of instructions supplied to a computer for the purpose of solving a problem or performing a specific task.

Aliasing When an analog signal is sampled for conversion into a digital data stream, the sampling frequency must be at least twice that of the highest frequency component of the input signal. If this rule is disobeyed, the sampling process becomes ambiguous as there are insufficient points to define each cycle of the waveform, resulting in enharmonic (false) frequencies being added to the audible signal. Aliasing is also sometimes referred to as fold-over.

All notes off A three byte MIDI channel message that instructs the receiving device to terminate all notes currently sounding.

Arpeggiate To play the notes of a chord in succession rather than simultaneously.

Arpeggiator Device (or software) that allows a MIDI instrument to sequence around any notes currently being played. Most arpeggiators also allows the sound to be sequenced over several octaves so that holding down a simple chord can result in an impressive repeating sequence of notes.

ASCII American Standard Code for Information Interchange. A coding convention to represent characters in 8-bit binary format. The first 128 characters are standard for almost all languages. The last 128 characters are language-specific.

ATR Audio tape recorder.

Attack The initial stage of an envelope. Refers to the time taken for a sound to achieve maximum amplitude. Drums have a fast attack, whereas bowed strings have a slow attack. In compressors and gates, the attack time equates to how quickly the processor can change its gain.

Autolocator Feature of a tape machine or other recording device that enables specific locations to be stored, then at some later time these locations within the recording may be recalled. For example, you may store the start of a verse as a locate point so that you can get the tape machine to wind back the start of the verse after you've recorded an overdub.

AVLS Automatic Volume Limiter System; on most Walkman personal stereos, circuitry that manages the audio signal to prevent distortion due to music crescendos and other volume peaks.

Band pass filter Filter that removes or attenuates frequencies above and below the frequency at which it is set. Frequencies within the band are emphasised. Band pass filters are often used in synthesisers as tone shaping elements. Often abbreviated to BPF.

Bank A storage location in a sampler or synthesiser that typically holds a large number of individual programs (sounds).

Bi-amplify The use of two amplifiers, one for the lows, one for the highs. Could be built into the speaker design or accomplished with the use of external amplifiers and electronic crossovers.

Boost/cut control A single control which allows the range of frequencies passing through a filter to be either amplified or attenuated. The centre position is usually the flat or no effect position.

Bouncing The process of mixing two or more recorded tracks and re-recording these on to another track.

BPM Beats per minute.

Breath controller Device that converts breath pressure into MIDI controller data.

Bulk dump A MIDI function that allow the transfer of system specific data, such as sample files or mixer settings, between MIDI capable devices. The data is transmitted as MIDI System Exclusive messages.

Channel (MIDI) Refers to one of 16 possible data channel over which MIDI data may be sent. The organisation of data by channels means that up to 16 different MIDI instruments or parts may be addressed using a single cable.

Channel (mixer) A single strip of controls in a mixing console relating to either a single input or a pair of main/monitor inputs.

Channel message A type of MIDI message that carries specific channel information.

Chord Three or more different musical notes played at the same time.

Chromatic A scale of pitches rising in semitone steps.

Clarity The ability of a speaker system to reproduce subtle details. Good transient response and an extended high end improve clarity.

Click track Metronome pulse which assists musicians in playing in time.

Console Alternative term for mixer.

Continuous controller A type of MIDI message that is generated by the movement of a continuous control, such as from a pedal, wheel or breath control device.

Crossover An electronic circuit that divides an audio signal into high- and low-frequency components. In many computer speakers, a crossover routes high-frequency sounds to satellite modules and low frequencies to the bass unit. The split point between the two is called the crossover frequency.

Crosstalk Unwanted breakthrough of one channel into another. Also refers to the distortion that occurs when some signal from a music source that you are not listening to leaks into the circuit of the source that you are listening to.

Cut-off frequency The frequency above or below which attenuation begins in a filter circuit.

Damping Refers to the ability of an audio component to stop after the signal ends. For example, if a drum is struck with a mallet, the sound will reach a peak level and then decay in a certain amount of time to no sound. An audio component that allows the decay to drag on too long has poor damping and less definition than it should. An audio component that is overdamped does not allow the initial energy to reach the full peak and cuts the decay short. Boomy or muddy sound is often the result of underdamped systems. Dry or lifeless sound may be the result of an overdamped system.

DAT Digital Audio Tape; an audio tape format that uses linear digital encoding to produce audio with the dynamic range and clarity of a CD on a cassette that is 30% smaller than a regular audiocassette. The commonly used DAT machines are more correctly known as R-DAT because they use a rotating head similar to a video recorder. Digital recorders using fixed or stationary heads (such as DCC) are known as S-DAT machines.

DIN plug A five-pin connector used by MIDI equipment.

Decay One of the four basic stages of an envelope. Refers to the time the sound takes to settle into its sustain level.

Delay A common effect in a sampler or synthesiser that mimics the time difference between the arrival of a direct sound and the first reflection to reach the listener's ears.

Dither Dithering is a mathematical process where a random noise is added to the least significant bit of a digital word. With very low level signals, the quantization error becomes correlated to the signal level. This creates a measurable amount of distortion. By adding dither, the correlation between the signal level and the quantization error is cancelled, allowing the digital system to encode amplitudes smaller than the least significant bit. If you change the word size as a signal passes from one digital system to another, being able to add dither allows you to maintain a high quality signal. Dither is absolutely required for good digital audio recording and processing.

Dolby noise reduction Circuitry designed and licensed by Dolby Laboratories, used to suppress noise (extraneous sound or interference) during recording and playback of audiocassettes. Dolby B and Dolby C both amplify weaker sounds during the recording process, and return them to correct levels during playback to increase dynamic range. Dolby S is the most advanced form. Used in record and playback modes, it can enhance an audiocassette deck's dynamic range to near CD quality.

Driver Piece of software that handles communications between the main program and a hardware peripheral, such as a soundcard, printer or scanner.

Drum machine An electronic device, usually controllable via MIDI commands, that contains samples of acoustic drum sounds. Used to create percussion parts and patterns.

Drum pad Synthetic playing surface which produces electronic trigger signals in response to being hit with drum sticks.

Dubbing Adding further material to an existing recording. Also known as overdubbing.

DSL (Dynamic Super Linear Bass) This electronically controlled equaliser circuit monitors low frequencies and automatically provides enhancement where roll-off occurs. DSL varies the compensation level according to the input signal level, resulting in deep, natural sounding bass response at all listening levels.

Ducking Ducking is used to automatically reduce signal levels when the level of a source signal exceeds a specified threshold. It is used for voice-over applications where, for example, level of background music is automatically reduced (made to "duck"), allowing an announcer to be heard clearly.

Dynamic Headroom The ability of an audio device to respond to musical peaks. For example, an amplifier may be capable of a sustained 100 watts only, but may be able to achieve peaks of 200 watts for the fraction of a second required for an intense, quick sound. In this example the dynamic headroom would equal 3 dB.

Effect Device for treating an audio signal in order to change it in some creative way. Effects often involve the use of delay circuits, and include such treatments as reverb and echo.

Electrostatic speaker A speaker that radiates sound from a large diaphragm that is suspended between high-voltage grids.

Effects loop Connection system that allows an external signal processor to be connected into the audio chain.

Effects return Additional mixer input designed to accommodate the output from an effects unit.

Electrostatic speaker A speaker that radiates sound from a large diaphragm that is suspended between high-voltage grids.

Equalizer Device for selectively cutting or boosting selected parts of the audio spectrum.

Error correction a procedure found in digital audio systems that detects and corrects inaccurate or missing bits in the data stream.

Expander An expander is another form of automatic level control. By attenuating the signal below the threshold, the expander reduces low-level noise or expands the dynamic range of the recorded material.

Extension How extended a range of frequencies the device can reproduce accurately. Bass extension refers to how low a frequency tone will the system reproduce, high-frequency extension refers to how high in frequency will the system play.

FX Short for "effects".

Gain To increase in level. The function of a volume control.

Gold plated plug Gold plating prevents oxidation of the plug's surface, minimising the contact resistance and transmission loss that occurs over time.

Graphic equaliser a device type that applies a series of band pass filters to a sound, each of which works on a certain range of the spectrum. The frequencies that fall within the range, typically one-third octave, can be boosted or cut. The name comes about because the fader positions provide a graphic representation of the EQ curve

Haas effect If sounds arrive from several sources, the ears and brain will identify only the nearest. In other words, if our ears receive similar sounds coming from various sources, the brain will latch on to the sound that arrives first. If the time difference is up to 50 milliseconds, the early arrival sound can dominate the later arrival sound, even if the later arrival is as much as 10 dB louder. The discovery of this effect is attributed to Halmut Haas in 1949.

Harmonic distortion The addition of harmonics that were not present in the original signal.

Harmonics Also called overtones, these are vibrations at frequencies that are multiples of the fundamental. Harmonics extend without limit beyond the audible range. They are characterised as even-order and odd-order harmonics. A second-order harmonic is two times the frequency of the fundamental; a third order is three times the fundamental; a fourth order is four times the fundamental; and so forth. Each even-order harmonic: second, fourth, sixth, etc. is one octave or multiples of one octave higher than the fundamental; these even-order overtones are therefore musically related to the fundamental. Odd-order harmonics, on the other hand: third, fifth, seventh, and up-create a series of notes that are not related to any octave overtones and therefore may have an unpleasant sound. Audio systems that emphasise odd-order harmonics tend to have a harsh, hard quality.

Headroom The ability of an amp to go beyond its rated power for short durations in order to reproduce musical peaks without distortion. This capability is often dependent on the power supply used in the design.

High-pass filter A filter which attenuates frequencies below its cut-off frequency.

Hiss Noise caused by random electrical fluctuations.

Hum Signal contamination caused by the addition of low frequencies, usually related to the mains power frequency.

Internet Radio Unlike regular AM and FM radio broadcasting, which is limited by official bodies which controlling frequencies and power ranges, all that is required to broadcast on the Internet is streaming audio software and space on an Internet server. This freedom has allowed thousands of stations to spring up in cyberspace. The entire range of musical and talk genres are well represented on the Internet.

ISO 9660 The universal file format for Yellow Book CD-ROM.

ISRC A 12-digit code written into the subcode area of an audio CD which holds logging information for each track.

Limiter Device that controls the gain of a signal so as to prevent it from ever exceeding a preset level. A limiter is essentially a fast acting compressor with an infinite compression ratio.

Loop To repeat a sequencer pattern or portion of an audio sample repeatedly. The point to which the program returns, whether the beginning or some other point, is usually definable by the user.

Low-pass filter A circuit or software algorithm which allows low frequencies to pass but rolls off the high frequencies. Most subwoofers have low-pass filters built in and many surround sound decoders have subwoofer outputs that have been low-pass filtered.

mA milliamp or one thousandth of an amp.

Magneto-optical recording system The digital recording/playback system used in the MiniDisc, which can record and re-record high-quality audio on a single disc many times. A high-powered laser heats a tiny portion of the magnetic coating of the rotating disc to the point where its magnetic orientation can be easily changed. Then a magnetic head writes the new audio information on the disc, which cools as it spins away from the laser.

Metronome A device or software function that produces a discrete pulse. Used to synchronise music with a specific tempo.

MIDI Musical Instrument Digital Interface. An international standard for communication between a musical instrument and a computer.

Mixer A recording device that allows several different audio sources to be combined. Provides independent control over each signal's loudness and stereo position.

Multiplex The ability to add or remove a pre-recorded lead singer's vocal from cassette tapes, CD+G discs and other Karaoke software. If your Karaoke software contains multiplex recording such as a duet, you can then use this feature to sing either one of the vocals.

Multitimbral Having the ability to produce many different musical timbres (sounds) at once.

Multitrack A recording device capable of recording several parallel parts or tracks which may then be mixed or re-recorded independently.

Nonlinear recording Describes digital recording systems that allow any parts of the recording to be played back in any order with no gaps. Conventional tape is referred to as linear, because the material can only play back in the order in which it was recorded.

Nonlinearity What goes into a system comes out changed by its passage through that system; in other words, distorted. The ideal of an audio component and an audio system is to be linear, or nondistorting, with the image on one side of the mirror identical to the image on the other side.

Octave A frequency ratio of 2:1. A musical distance (interval) of 12 semitones. When a frequency or pitch is transposed up by one octave, its frequency is doubled.

Off-line Process performed while a recording is not playing. For example, some computer-based processes have to be performed off-line as the computer isn't fast enough to perform the process in realtime.

Overdub To record one sound on top of another; to add another part to a multitrack recording or to replace one of the existing parts.

Pan To move a signal from the left to the right of a stereo field, or vice versa.

Pan pot Control enabling the user of a mixer to move the signal to any point in the stereo sound stage by varying the relative levels fed to the left and right stereo outputs.

Parameter A variable value that affects some aspect of performance.

Pitch A continuous frequency over time.

Pitch shifter Device for changing the pitch of an audio signal without changing its duration.

Plugins Accessories that add functionality to a digital audio software. They range from input plugins that allow your player to read different file formats to output plugins that provide visual displays to accompany your music. Visualisation modules and digital signal processors are types of plugins.

Polyphonic The ability to play many different notes at once.

Portamento A gliding effect that allows a sound to change pitch at a gradual rate, rather than abruptly.

Punch-in The action of placing an already recorded track into record at the correct time during playback, so that the existing material may be extended or replaced.

Punch-out The action of switching a tape machine (or other recording device) out of record after executing a punch-in. With most multitrack machines, both punching in and punching out can be accomplished without stopping the tape.

Push-pull Most common type of amplification that amplifies the negative and positive sides of the waveform separately. Allows for much higher power output than single-ended.

Quantization The encoding process when the analog input is approximated (quantized) to the nearest binary value available. In a sequencer, used to adjust recorded material so it will be performed precisely on a selected division of the beat.

Realtime A recording or realisation of a sound processing procedure as it occurs (being recorded or played back). The opposite is off-line, where the signal is processed in non-realtime.

Red book The formal standard for the audio compact disc, developed by Philips and Sony in 1982.

Release The time taken for a level or gain to return to normal. Often used to describe the rate at which a synthesised sound reduces in level after a key has been released.

Sequencer Software or, less commonly, a hardware device that can record, edit and playback a sequence of audio data.

Spectral balance Balance across the entire frequency spectrum of the audio range.

Step time Entering notes one by one, as opposed to realtime recording in a sequencer.

Streaming (audio) Refers to the process of making a broadcast of audio available on the Internet. Basically, the broadcaster puts together a set of songs and plays them from their Internet server. They then make the server available to other Internet users. The increasing availability and quality of Internet access has led to a massive proliferation of such broadcasters. This is because anyone with the right pieces of software and Internet server space (which virtually anyone with Internet access can obtain for free) can administer an Internet audio stream. Most digital audio player software applications can play Internet audio streams.

Stripe To record time code onto one track of a multitrack tape machine.

Sub bass Frequencies below the range of typical monitor loudspeakers. Some define sub-bass as frequencies that can be felt rather than heard.

Subwoofer A speaker designed to deliver extremely low-frequency sound (usually below 100 Hz). A true subwoofer should be able to at least reach into the bottom octave (20-40Hz). Active subwoofers have built-in crossover circuitry to filter the low-frequency signal.

Sweet spot The optimum position for a microphone, or for a listener relative to monitor loudspeakers.

Tempo the rate of speed at which a musical composition proceeds (i.e. the beat). Usually uses a quarter note as the timing reference.

Timbre The quality of a sound that distinguishes it from other sounds of the same pitch and volume. The distinctive tone of an instrument or a singing voice. Tone colour.

Track The term dates back to multitrack tape where the tracks are physical stripes of recorded material, located side by side along the length of the tape.

Transpose To shift a musical signal by a fixed number of semitones.

Tremelo A rapid alternation of two tones, usually a third apart.

Tweeter A speaker used to reproduce the higher range of frequencies. To form a full-range system, a tweeter needs to be combined with a woofer, (2-way system), or a woofer and midrange, (3-way system).

Unison To play the same melody using two or more different instruments or voices.

Vibrato Pitch modulation.

Woofer A speaker used for low-frequency reproduction. Usually larger and heavier than a midrange or tweeter.

Yellow book The formal basic standard for storing computer data on a compact disc, i.e. CD-ROM.

Zipper noise Audible steps that occur when a parameter is being varied in a digital audio processor