Digital Audio Corporation PCAP II, Руководство пользователя

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110
milliseconds is generally recommended for speech
applications.
The gain algorithm dynamically adjusts the signal
amplification based on input signal level and its
Gain Region
(limiting, compression, or expansion). If the input signal level
exceeds the
Limit Threshold , it is in the Limit region. If the
input signal level exceeds the Compression Threshold , but
not the Limit Threshold , it is in the Compression region.
And, lastly, if the input signal level is below the
Compression Threshold , it is in the Expansion region. The
three Gain Regions are described below:
Limit Region : In the limit region the output signal
level is “damped” or kept from exceeding the
specified
Limit Threshold by applying attenuation.
Compression Region
: In this region the output
signal level changes at a fraction of the rate of the
increase of the input signal level. The dynamic range
of the output signal is thus is reduced with respect to
the input signal. As an example, a 2:1 compressor
would produce an output level decrease of only 10 dB
when the input signal decreases 20 dB.
Compression allows signals of wide dynamic ranges
to be squeezed into more limited dynamic ranges of
recording media and transmission channels.
Compression also eases listening, especially for
noisy audio. Compressors are generally preferred
over AGC's since input signal level differences are
more are modestly preserved.
Expansion Region
: In the this region the output
signal has a wider dynamic range than the input
signal. Expansion is the opposite of compression.
As an example, with an expansion ratio of 1:3, the
output signal will decrease 30 dB when the input
signal decreases only 10 dB. Expansion may be
used to restore a signal's dynamic range following
compression; for example, if a 2:1 compression has
taken place, a 1:2 expansion would restore the
signal to its original dynamic range. Expansion is
also used to attenuate objectionable low-level
background sounds that are below voices.