Lexicon 20/20 AD manual Definition of Terms

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Definition of Terms

AES : Audio Engineering Society.

aliasing : a form of distortion which occurs when an A/D converter’s sample rate is less than twice the highest fre- quency component of a signal.

amplitude : the maximum departure of the value of a wave- form from its average value.

attenuation : a reduction in the amplitude of an audio signal.

balanced signals : two equal and opposite signals run through a twisted pair. The advantage of balanced signals is that common mode noise tends to be added equally to both portions of the pair; it can be removed by subtracting the negative from the positive signal. (Common mode noise rejection cannot be performed on unbalanced signals, which consist of an audio signal and a ground return.)

bandwidth : the arithmetic difference between the upper and lower cut-off frequencies of an audio system.

bit : binary digit: the smallest unit of digital information, equivalent to the result of a choice between two alternatives (yes or no, on or off , 0 or 1). A series of bits make up a binary number called a sample word.

common mode noise :any signal which is common to both the negative and positive polarity of a balanced signal. In a typical audio signal, common mode noise is introduced over the length of the cable by outside interference. A typical example is line hum.

CMRR : Common Mode Rejection Ratio: measures the ability of a system to reject common mode noise. It is expressed as the ratio of common mode noise entering the system to the common mode noise leaving it.

dBfs : decibel full scale: this is the unit used to describe the amplitude of a digital audio signal where 0 equals digital full scale.

digital headroom : does not exist, see dBfs.

distortion : an unwanted change in a waveform as it passes through an electronic component or from one medium to another.

dither : a low level signal which is added to digital audio to reduce quantization noise, in effect, by replacing it with noise which is perceived as less offensive.

dynamic range : when used to describe digital-to-analog or analog-to-digital converters, dynamic range is the ratio of the full scale signal to the broadband noise (0-20 kHz) measured with a -60dBfs signal. In other words, it is the S/(N+D) measured with a -60 dBfs input signal and a 20 kHz low-pass filter.

EBU : European Broadcast Union.

emphasis : a form of equalization which increases high frequency signals in order to maximize the signal-to-noise ratio. De-emphasis is the inverse of emphasis.

equalization : the process of increasing or decreasing the amplitude of some frequency ranges of a signal with respect to others.

frequency : the number of vibrations per unit of time, ex- pressed in cycles per second (Hz).

harmonic distortion : the appearance of harmonics of the input signal at the output of a device.

link : the tying of two channels of the 20/20 AD compressor to a shared gain curve.

lock : two or more audio signals which have the same frequency and phase.

mS : millisecond: 1/1000 of a second.

oversampling : a method of sampling an audio signal at many times the audio bandwidth (typically, 64-256 times) in order to reduce the complexity of the anti-aliasing filter. The oversampled data is then digitally filtered to reduce the sample rate.

period : the interval of time required for a waveform to complete one cycle and begin to repeat itself. Period = 1/ frequency.

phase : the angular relationship between two signals, meas- ured in degrees, where 360° = the period of the waveform. When two identical signals are always of the same polarity, they are said to be in phase, or to have a phase of 0° . When they are always of opposite polarity, they are said to be out of phase, or to have a phase of 180° .

polarity : the positive or negative direction of an electrical force.

quantization : the process of converting an infinitely-varying waveform into a finite series of discrete levels. The inaccuracy introduced by this process is called quantization error.

rms amplitude : root mean squared amplitude: a way of assigning a DC power equivalent to an AC waveform. For a sine wave, this is 0.707 times the peak level.

sample rate : the periodic interval at which an analog audio signal is sampled, e.g. 44.1 or 48 kHz.

signal-to-noise ratio : the ratio between the maximum peak signal and the wideband noise in the absence of signal. This number becomes more meaningful when distortion is added. It is then expressed as S/(N+D).

S/PDIF : Sony/Phillips Digital Interface Format.

synchronize : to arrange events to occur simultaneously. In audio, the events are both the period and the phase of a signal.

THD+N : the ratio of the rms amplitude of the distortion and noise that is added to a signal to the rms amplitude of the signal itself. This can be expressed in percent or decibels. S/ (N+D) = 1/(THD+N).

time constant : the amount of time it takes for a signal to rise or fall 63% of its full scale. This only pertains to signals which rise and fall exponentially, such as the 20/20 AD meter time constants or compression gain curves.

word clock : a square wave used as a synchronization source. Its frequency equals the sample rate.

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Contents 20/20 AD Precautions Electrostatic Discharge ESD Precautions Contents Introduction AES/EBU Interface ProfessionalControls and Connectors Power Mounting20/20 AD Front Panel Controls ConverterDisplay Level MetersCompressor LinkSynchronization Output Formatting Alternate ModesPress and hold Then press one of these 20/20 AD Rear Panel Connectors BAL/UNBALConnectors Audio ConnectionsXLR Pinout Cables Signal Type Attenuator DBu DBV Signal Type Pin Pin3Termination and Grounding via Internal Jumpers These instructions are for use by qualified personnel only Word ClockAnalog Jumpers Balanced Unbalanced Input Signals Front panel Adjustments DB ScaleMeter Ballistics Synchronization and Sample Rate AES Sync Word ClockStates Internal and External modesAbout Dither Psychoacoustically Optimized Noise Shaping Pons00k 10.0k 12.0k 14.0k 16.0k 18.0k Automatic Offset Removal Compressor Modes Dynamic Range CompressionInput Compressor Knob Values Gain Threshold ReleaseNon-linear Transfer FunctionsUsing the 20/20 AD Lexicon Link Realigning Two DAT Recordings Digital Sinewave GeneratorGain Definition of Terms Definition of Terms Oak Park Bedford, MA 01730 USA Tel Fax