Digital Audio Midterm Vocabulary

A/D converter Circuit for converting analog waveforms into a series of equally spaced numerical values represented by binary numbers. The analog signal is sampled every few milliseconds and its level is quantities into a digital word. The larger the digital word (i.e. the more 'bits'), the more accurate the digital representation of the analog value.

AC3 Dolby Digital Format

AES/EBU interface A two-channel, digital audio hardware/software standard. The AES/EBU interface allows for data communication between professionally-oriented digital devices such as digital signal processors, hard disk recording systems, synthesizers with AES/EBU outputs,digital audio workstations, etc. Standard IEC-958 defines this interface; it uses XLR type connectors.

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

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.

AM wide-band tuner Picks up higher frequency range AM signals (from 1610kHz to 1710kHz) to receive newly allocated additional stations.

AMP Ampere; unit of electrical current.

Amplifier A device which increases signal level. Many types of amplifiers are used in audio systems. Amplifiers typically increase voltage, current or both. The resulting signal is a reproduction of the input signal as well as this increase.

Amplitude Another word for level. Can refer to sound levels or electrical signal levels. It is the height of a waveform. The greater a sound wave's amplitude, the louder it sounds.

Analog audio The traditional means of recording and reproducing sound, using fluctuating electronic voltages to replicate audio waveforms. The origin of the term is that the electrical signal can be thought of as being analogous to the original signal.

ADC Analog-to-Digital converter.

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.

Attenuate To make lower in level.

Audio frequency Signals in the human audio range: nominally 20Hz to 20kHz.

Balance The relative levels of the left and right channels of a stereo recording, or the relative levels of the various instruments and voices within a mix.

Balanced audio signals Signals that are carried on three-conductor cables, with two of the conductors carrying the same signal 180 degrees out of phase and third as ground. Balanced connections usually cost more than unbalanced connections but are less susceptible to picking up hum and interference with low-level signals.

Balanced wiring Wiring system which uses two out-of-phase conductors and a common screen to reduce the effect of interference. Audio signals require two wires. In an unbalanced line the shield is one of those wires. In a balanced line, there are two wires plus the shield. For the system to be balanced requires balanced electronics and usually employs XLR connectors. Balanced lines are less apt to pick up external noise. This is usually not a factor in home audio, but is a factor in professional audio requiring hundreds or even thousands of feet of cabling. Many higher quality home audio cables terminated with RCA jacks are balanced designs using two conductors and a shield instead of one conductor plus shield. For balancing to be effective, both the sending and receiving device must have balanced output and input stages respectively.

Bandwidth A means of specifying the range of frequencies passed by an electronic circuit such as an amplifier, mixer or filter. The frequency range is usually measured at the points where the level drops by 3dB relative to the maximum. So a system's bandwidth is the total frequency range of the system, usually specified as something like: 20-20,000Hz plus or minus 3 db.

Bias High frequency signal used in analog recording to improve the accuracy of the recorded signal and to drive the erase head. Bias is generated by a bias oscillator.

Binary (numbers) A numbering system based on 2 in which 0 and 1 are the only available digits.

Bit Binary digit; a single unit of digital data. It can have a value of 1 or 0, sometimes equivalent to yes/no, true/false or similar, but often it is part of a larger byte or word to make up a specific number. Usually 8 bits equals one byte, however MIDI uses a 10 bit byte that includes a start bit, the 8-bit data message, and a stop bit.

BNC A type of connection often used in instrumentation and sometimes in digital audio. BNC connectors sometimes are used for digital connections such as from a CD transport

Buffering The method for temporarily storing or delaying data samples before processing or conversion.

Burning This term usually refers to the act of writing information (data, music, etc.) on to a compact disc.

Byte A piece of digital data comprising (normally) eight bits. See also Bit.

Capacitance Property of an electrical component able to store electrostatic charge.

Capacitor microphone Microphone that operates on the principle of measuring the change in electrical charge across a capacitor where one of the electrodes is a thin conductive membrane that flexes in response to sound pressure.

Cardioid Meaning heart shaped, describes the polar response of a unidirectional microphone.

CD Compact disc.

CD-R A recordable compact disc format, allowing just one record cycle (it cannot be erased and reused).

CD-R burner A device capable of recording data on to blank CD-R discs.

CD-RW A rewritable CD. Unlike record-once CDs (CD-Rs) you can erase and re-record a CD-RW a thousand times or more.

Chorusing A doubling effect commonly found on a synthesizer or sampler that makes a single sound appear to sound like an entire ensemble. The initial signal is split and appears at a slightly altered pitch from the original, or at a slightly later point in time. This time and pitch level are often controllable by a low frequency oscillator (LFO).

Clipping Distortion that occurs when an amplifier is driven to play louder than its power supply will allow. Usually the clipped waveform contains an excess of high-frequency energy. The sound becomes hard and edgy. Hard clipping is the most frequent cause of burned out tweeters. Even a low-powered amplifier or receiver driven into clipping can damage tweeters which would otherwise last virtually forever.

Coaxial A speaker type that utilizes a tweeter mounted at the centre of a woofer cone. The idea being to have the sound source through the full frequency range become coincident.

Codec Acronym for Compressor-Decompressor; the complicated mathematical algorithms used to create and read compressed digital audio files. There are several MP3 codecs that vary widely in their quality and efficiency.

Compression In audio, compression means to reduce the dynamic range of a signal. Compression may be intentional or one of the effects of a system that is driven to overload.

Compressor A compressor provides a form of automatic level control. It attenuates high levels, thus effectively reducing the dynamic range, making it much easier to control signals and set appropriate fader levels. Reducing the dynamic range also means that recording levels can be set higher, therefore improving the signal-to-noise performance. Limiting is an extreme form of compression, where the output signal is sharply attenuated so that it cannot exceed a particular level.

Cycle One complete vibration of a sound source or its electrical equivalent. One cycle per second is expressed as 1 Hertz (Hz).

DAC Converter Circuitry that converts a digital (binary) signal into an equivalent analog waveform. In an audio system, this is done so the signal from digital storage media, such as MiniDisc, CD, or Digital Audio Tape, can be handled by analog system components, such as the receiver and speakers. Often abbreviated to just D/A or DAC.

Data compression A system for reducing the amount of data stored by a digital system. Most audio data compression systems are so-called lossy systems as some of the original signal is discarded based on psycho acoustic principles designed to ensure that only components which cannot be heard are lost.

dB deciBel; one-tenth of a Bel, a unit of measurement (named after Alexander Graham Bell) that describes the strength of a signal relative to a standard reference. Different kinds of decibels measure a variety of signal types. One type, dBv, compares an electrical signal such as amplifier output with a 1-volt standard. Another type, dBr, can be used to measure the output of a speaker system relative to a reference sound level that represents the lower threshold of human hearing. 0 dB is the threshold of hearing, 130 dB is the threshold of pain

· Whisper: 15-25 dB

· Quiet 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

DC Direct Current; an electrical current that flows in one direction.

Decoding This is the process whereby the information in a compressed digital audio file is read so that it can be played and heard. Software MP3 players like UltraPlayer and Winamp decode and play MP3 files.

De-esser Device for reducing the effect of sibilance in vocal signals.

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

DI box Device for matching the signal level impedance of a source to a tape machine or mixer input.

Digital Audio Refers to a way of synthesizing sound. In a digital format sound waves are broken down and assigned a numerical value, represented by groups of 1s and 0s. When these groups of numbers are read by a receiver or amplifier, they are converted back into sound. This kind of mathematical precision creates crisp, clean sounds.

Distortion Anything that alters the musical signal (a process often found desirable by guitar players). There are many forms of distortion, some of which are more audible than others. Distortion specs are often given for electronic equipment which are quite meaningless. As in all specifications, unless you have a thorough understanding of the whole situation, you will not be able to make conclusions about the sonic consequences.

Dolby Digital A five-channel system consisting of left, centre, right and left rear, right rear channels. All processing is done in the digital domain. Unlike Dolby Prologic in which the rear effects channels are frequency limited to approx. 100-7000Hz, Dolby Digital rear channels are specified to contain the full 20-20Khz frequency content. The AC3 standard also has a separate sub woofer channel for the lowest frequencies.

Dolby Prologic A four-channel system consisting of left, centre, right and rear channel, (the single rear channel is usually played through two speakers).

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

DVD Acronym for Digital Versatile Disc, a standard that seeks to combine better-than-laser-disc quality video with better-than-CD quality audio in a disc the size of a CD. Requires special players.

DVD-Audio Audio format based on the DVD standard, features very high quality audio (96kHz, 24-bit) as well 5.1 Surround Sound (up to six channels).

DVD-ROM Computer data format based on the DVD standard; uses the UDF file format and offers up to 4.9 GB of data storage on each layer.

Dynamic microphone A type of microphone that works on the electric generator principle, where a diaphragm moves a coil of wire within a magnetic field.

Dynamic Range The difference between the loudest (maximum output level) and quietest (residual noise floor) sounds produced in an audio system without distortion. The dynamic range in a digital system is determined by the data resolution, about 6 dB per digital bit. A 20-bit system has a theoretical dynamic range of 120 dB. In speech, the range rarely exceeds 40 dB; in music, it is greatest in orchestral works, where the range may be as much as 75 dB.

Dynamics the relative loudness or softness of a piece of music.

Echo the repetition of a sound delayed in time by at least 50 milliseconds after the original. An effect often found in synthesizers and samplers.

Encoding This is the name for the process in which larger sound files are compressed into smaller ones. When you convert a file from WAV format into an MP3 file, you are encoding. When you record a song from a CD into MP3 format, you are ripping and encoding it.

Fade in/out A feature of most audio editing software that allows the user to apply a gradual amplitude increase or decrease over some segment of the sound.

Figure-of-eight Describes the polar response of a microphone that is equally sensitive both front and rear, yet rejects sounds coming from the sides.

Filter a circuit or software algorithm which permits certain frequencies to pass easily while inhibiting or preventing others. Typical filters include low pass, high pass, band pass, and band reject.

Flange an effect applied to a sound where a delayed version of the sound (feedback) is mixed with the original to create a dramatic, sweeping sound.

Fletcher-Munson curve Our sensitivity to sound depends on its frequency and volume. Human ears are most sensitive to sounds in the midrange. At lower volume levels humans are less sensitive to sounds away from the midrange, bass and treble sounds seem reduced in intensity at lower listening levels

Frequency the rate per second at which an oscillating body vibrates. Usually measured in Hertz (Hz), humans can hear sounds whose frequencies are in the range 20 Hz to 20kHz.

Frequency response A measure of a component's ability to reproduce all frequencies at their correct volumes. Frequency-response curves show whether a speaker outputs certain frequencies too loudly or softly. Excessive fluctuations in a curve indicate colorations, which can result in muddy, tinny, or boomy sound.

Fundamental frequency The predominant frequency in a complex waveform. Typically provides the sound with its strongest pitch reference. Any sound comprises a fundamental or basic frequency plus harmonics and partial at a higher frequency.

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 characterized 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 emphasizes odd-order harmonics tend to have a harsh, hard quality.

Hertz (Hz) A unit of measurement denoting frequency, originally measured as cycles per second, (CPS): 20 Hz = 20 CPS. Kilohertz (kHz) are Hertz measured in multiples of 1,000.

Impedance Impedance is a measure of electrical resistance specified in ohms. Speakers are commonly listed as 4 or 8 ohms but speakers are reactive devices and a nominal 8 ohm speaker might measure from below 4 ohms to 60 or more ohms over its frequency range. This varying impedance curve is different for each speaker model and makes it impossible to design a really effective generic speaker level high-pass filter. Active devices like amplifiers typically have an input impedance between about 10,000-100,000 ohms and the impedance is the same regardless of frequency.

Jitter Timing variations, a tendency towards lack of synchronization caused by electrical changes. Technically the unexpected (and unwanted) phase shift of digital pulses over a transmission medium. A discrepancy between when a digital edge transition is supposed to occur and when it actually does occur. Think of it as nervous digital, or maybe a digital analogy to wow and flutter.

kHz 1000 hertz

kOhm 1000 ohms

MIC level The low level signal generated by a microphone. This must be amplified many times to increase it to line level.

Monophonic The ability to play only one note at a time. A characteristic of some older synthesizers.

MP3 Stands for MPEG-1, Audio Layer 3. MP3 is a digital audio file format. It is currently the most popular format on the web because of its high sound quality and small file size, and because MP3 encoders are easily available on the Internet. The file extension for an MP3 file is usually ".mp3".

MPEG MPEG is a term used generically to identify files created using standards developed by the Motion Pictures Expert Group. The Motion Pictures Expert Group is an international organization that develops and maintains standards for digital formats for video and audio. The group was originally formed to maintain consistent formats to be used to compress and distribute films. Version and Layer numbers identify the group's different compression formats for digital video and audio. The standards maintained by the Motion Pictures Expert Group allow engineers to build encoders and decoders for compressing and reading digital video and audio. If the standard for a certain format is followed, files created by one engineer's encoder should be readable by another engineer's decoder.

MPEG-1 The earliest form of digital compression used by the DSS program providers to transmit audio/video information. The main advantage of MPEG technology is the transmission of more channels in what is normally a limited amount of space or band width.

MPEG-2 The most advanced form of digital compression, currently used by the DSS program providers to transmit audio/video information. It continues to have all the advantages of MPEG-1 but also helps improve certain picture quality transmission problems, e.g., motion tiling. The program providers started using this new compression technology in mid- to late-1995.

Muddy Listening term. A sound that is poorly defined, sloppy or vague. For example, a muddy bass is often boomy with all the notes tending to run together.

Normalization An automatic process available in most audio software whereby the gain of all program material is adjusted so the peak level will just arrive at 0 dBFS. Normalization can be extremely damaging to your digital audio if misused. The first serious peril is that it is a mistake to use Normalization to try to correct the apparent loudness of different songs on an album. In many cases, Normalization may aggravate an existing condition. The second peril of Normalization is that the very process of changing gain can add a veil or truncation distortion if improperly done.

Nyquist frequency The highest frequency that any given digital audio system can capture. Defined as one half the sampling rate of that system.

Nyquist sampling theorem Defines the process of sampling audio with a digital system. Among other things, it states that the sampling frequency of a digital audio system must be at least twice that of the highest audio frequency, otherwise aliasing will occur. The Nyquist theorem was developed at Bell Labs by C. Shannon and H. Nyquist.

Ohm Unit of electrical resistance.

Oscillator An electronic device capable of generating a recurring waveform, or a digital process to generate the same.

Out of phase An audio signal that has its waveform 180 degrees out of phase with another.

Overload A condition in which a system is given too high an input level. A common cause of distortion or product failure.

Oversampling A digital filtering technique used in CD components. Extra data points are added to the audio read from a disc, creating a signal that is some multiple (usually two, four, or eight times) of the CD format's standard sampling frequency. This process raises the frequency of any false information, which can then be removed by an analog filter. Using the high sample rate, the digital data may be processed with a very steep slope digital filter. As the filter is in the digital domain, unpleasant side-effects, such as phase effects are eliminated.

PCM Pulse Code Modulation. A scheme for encoding audio data as a series of pulses. Each pulse defines a transition from binary one to binary zero.

Peak Maximum instantaneous level of a signal.

Phase The relative position of a wave to some reference point; the frequency coherence of a signal; the timing difference between two electrical waveforms expressed in degrees, where 360 degrees corresponds to a delay of exactly one cycle. If two signals are "out of phase", the trough of the first waveform corresponds with the peak of the second, resulting in cancellation.

Phaser Effect which combines a signal with a phase shifted version of itself to produce creative filtering effects. Most phasers are controlled by means of an LFO.

Pitch A continuous frequency over time.

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. Visualization modules and digital signal processors are types of plugins.

Preamplifier A device that takes a source signal, such as from a turntable, tape deck or CD player, and passes this signal on to a power-amplifier. The preamplifier may have a number of controls such as source selector switches, balance, volume and possibly tone controls. Often shortened to "preamp".

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

Resolution The accuracy with which an analog signal is represented by a digitizing system. The more bits are used, the more accurately the amplitude of each sample can be measured, but there are other elements of converter design that also affect accuracy. High conversion accuracy is known as high resolution.

Resonance The characteristic of a filter that allows it to selectively pass a narrow range of frequencies.

Reverb Acoustic ambience created by multiple reflections in a confined space.

RF Radio Frequency.

RF interference Interference significantly above the range of human hearing.

Ripping Ripping is the process of taking audio data from your CD and making it into a sound file on your computer. It is called ripping because in most cases the audio data is digitally "ripped" directly from the CD. This process can be very fast (a four minute song might only take 30 seconds to record). An analog recording process on the other hand records a song by playing the CD and recording the sound output. The analog process can only happen in realtime (a four minute song takes four minutes to record). The digital extraction process is faster because it copies the data instead of recording the sound output. Software applications that rip from CDs create the new audio file in the WAV or AIFF formats. Software applications that rip and encode usually create the new audio file in the MP3 format.

Sample A digitized sound used as a musical sound source in a sampler or additive synthesizer.

Sample rate A digital representation of an analog signal created by checking, or sampling, the analog voltage a fixed number of times per second. The greater the number of samples, the more accurate the representation of the analog signal. The CD uses a sampling rate of 44.1kHz; it checks the analog signal 44,100 times per second.

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

Stereo From the Greek meaning solid. The purpose of stereo is not to give you separate right and left channels but to provide the illusion of a three-dimensional, holographic image between the speakers.

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

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.

VU meter Meter designed to interpret signal levels in roughly the same way as the human ear, which responds more closely to the average levels of sounds rather than to the peak levels.

WAV A digital audio file format. It is not a compressed format, so WAV files are usually very large. It is often used as an intermediate format when recording from a CD. WAV files can be compressed as MP3 files. The file extension for a WAV file is ".wav".

Waveform A graphic representation of the way in which a sound wave or electrical wave varies with time.

Wavelength The distance the sound wave travels to complete one cycle. The distance between one peak or crest of a sine wave and the next corresponding peak or crest. The wavelength of any frequency may be found by dividing the speed of sound by the frequency. (Speed of sound at sea level is 331.4 metres per second, that's 1087.42 feet per second).

White noise A random noise that contains an equal amount of energy per frequency band. That is, 100-200, 800-900, and 3000-3100. Pink noise has an equal amount of energy per octave. The bands 100-200, 800-1600, and 3000-6000 all contain the same amount of energy.

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

XLR Type of connector commonly used to carry balanced audio signals, including the feeds from microphones.