D-9
Rev 2.2, 10/31/94
Release Time
The release time of a dynamics processor is the time required for the processor's gain to
return to its nominal value, after the controlled signal exceeds (or doesn't exceed) a preset threshold.
See
also:
attack time, compressor, expander
.
Reverberation
The remainder of sound that exists in a room after the source of sound is stopped is
called reverberation, sometimes mistakenly called "
echo
." The time of reverberation is defined as the time
it takes for the sound pressure level to decay to one-millionth of its former value. This is a 60-decibel
reduction in level.
All rooms have some reverberation, and an important subjective quality of a room is its reverberation
time, although other factors, such as ratio of direct to reverberant sound, are probably more important.
In a real room, the sound heard by a listener is a mixture of direct sound from the source and
reverberant sound from the room. Reverberant sound is diffuse, coming from random directions, and the
direct sound allows us to localize the source of they sound. (TAD, abridged)
Ribbon Microphone, Velocity Microphone
A type of microphone which usually has a polar pattern shaped
like a figure 8. The first velocity microphone was the ribbon microphone, invented about 1931 by Harry
F. Olson of RCA research laboratories.
The ribbon microphone uses as an active element a small corrugated strip of very thin aluminum ribbon
hanging loosely in a strong magnetic field. The ribbon is moved by the action of air molecules, which are
set in motion by the sound wave. the resonant frequency of the ribbon is very low, below the audible
range, so the motion of the ribbon is "mass controlled," or is proportional to the velocity of the air
particles. For this reason, it is called a "velocity microphone". (TAD) The motion of the ribbon within the
magnetic field generates electricity, which is the microphone's output signal.
S/PDIF
An acronym standing for Sony-Phillips Digital Interface Format. This term describes an
interconnection standard/method commonly used for consumer-grade digital audio devices. The reason
Sony and Phillips are jointly named is because they are the two companies that developed the Compact
Disc. S/PDIF signals carry two audio channels as well as status information. The signal is unbalanced
and RCA connectors are typically used for interconnection between devices. The format of S/PDIF signals
is somewhat similar to the AES/EBU format.
Sampling Rate
In a digital audio system, the audio signal must be fed into an
analog-to-digital converter
(ADC) to be changed into a series of numbers for further processing by the system. The first step in this
is sampling, where the instantaneous signal amplitude is determined at very short intervals of time.
Sampling
must be done very accurately to avoid adding distortion to the digitized signal. The sampling
rate, which is the number of samples per second, must be uniform and precisely controlled. (TAD,
abridged) see also
:
quantization
.
Shelving Equalizer
An
equalizer
whose
frequency response
curves rise (or fall) to a maximum value,
remaining at that value to the limits of audibility. The bass and treble controls on most home stereo
amplifiers are shelving equalizers.
Sibilance
Vocal recordings, especially if made with very close microphones, are often characterized
by excessive loudness of the voice sibilants, and this effect is sometimes called "sibilance." The most
difficult sibilants to reproduce accurately are the sounds "s" and "sh." (TAD) see also
:
de-esser
.
Single-D Microphone
A single-D microphone is a directional microphone having only one entrance for
off-axis sounds. Single-D microphones exhibit a property called
proximity effect
, which is a boosting of
low frequencies when the microphone is used close-up to the sound source.
See also:
variable-D
microphone
.
Slapback, Slap Echo
The single repetition of a signal at a fixed time delay to simulate an echo from a
single reflecting surface, as opposed to a multiple echo from a time delay, where the delayed signal is
repeatedly fed back into the delay input. (TAD)
Sysex
A
MIDI
message (command) that stands for System Exclusive. MIDI sysex messages are
commonly used for controlling audio processors or other MIDI instruments. The sysex message exists to
allow programming/controlling beyond that which is predefined in the MIDI specification.
Threshold
A parameter commonly associated with dynamics processor and used to refer to a signal
level at which processing begins or ends. In a compressor, the threshold level is that signal level where
the change in level at the output no longer equals the change in level at the input.
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