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Definition of Terms
29
20/20 AD User Guide
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.
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.
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.)
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.
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
(
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.
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.
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.
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.
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.
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.
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.
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.
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).
pressed in cycles per second (Hz).
harmonic distortion : the appearance of harmonics of the
input signal at the output of a device.
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.
a shared gain curve.
lock : two or more audio signals which have the same
frequency and phase.
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.
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.
complete one cycle and begin to repeat itself. Period = 1/
frequency.
phase : the angular relationship between two signals, meas-
ured in degrees, where 360
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
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.
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.
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.
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 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).
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.
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).
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.
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.
source. Its frequency equals the sample rate.