5. APPLICATION NOTES
5.5.
Selection of
parameters to
increase loudness
Signal compression and the loudness enhancement of the digital
audio signal resulting from it can be achieved by combining two
dynamic range control processes: firstly, the
compression
achieved by increasing small and medium signal levels and
secondly,
linear amplification
combined with the inaudible
limitation
of individual, remaining peak levels with the limiter.
In the gain change mode the operation of compressor and limiter
can be observed on the display. For smaller signal levels the
compressor causes additional amplification which however
decreases the higher the signal level is . With full scale levels the
compressor is practically ineffective so that even an increase of
the RATIO will have no effect.
If you now increase the linear amplification GAIN, individual peak
levels are raised above the limiter threshold and limited inaudibly.
All other signal components can however be increased. If the gain
is too large also medium levels are treated by the limiter, which
means that the limiter then reduces the signals continually and
again reduces the additionally applied amplification.
The display for Limiter-Gain-Reduction should be in the region of
0...-6...-8 dB and should not light up red continuously, so that a
dynamic limitation only applies to signal peaks. Then the signal
compression and therefore also the increase of loudness is at its
most effective.
5.6.
Redithering -
Reduction of word
length of digital
output signal
At the end of postproduction the material must be prepared for
copy on COMPACT DISC. The information of a 24 bits signal is
not more storable linear. One must shorten 24 bits data word to 16
bit word length. The practice offers several procedures for it.
In the simplest case, the last bits are cut off - truncation. One
requires no further processing to this, it is enough to record a 20or
24 bits signal direct on a 16 bits storage medium. In this case, a
not unimportant quantization mistake however results, the part of
the harmonious distortions increases. Single numeric roundoff of
the signal to 16 bits reduces this mistake. Nevertheless, the result
will normally be worse than the data by the same original analog
signal converted with a good 16 bit ADC.
truncation
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