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authorJeffrey Goode <jeffg7@gmail.com>2009-11-04 18:14:36 +0000
committerJeffrey Goode <jeffg7@gmail.com>2009-11-04 18:14:36 +0000
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Compressor: simplify makeup gain setting, expand release range, finally provide documention in the manual!
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@23518 a1c6a512-1295-4272-9138-f99709370657
Diffstat (limited to 'manual/configure_rockbox/sound_settings.tex')
-rw-r--r--manual/configure_rockbox/sound_settings.tex58
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diff --git a/manual/configure_rockbox/sound_settings.tex b/manual/configure_rockbox/sound_settings.tex
index 3e78dd65f5..53272afba1 100644
--- a/manual/configure_rockbox/sound_settings.tex
+++ b/manual/configure_rockbox/sound_settings.tex
@@ -445,18 +445,48 @@ experience with more complex audio.
}
\opt{swcodec}{
-\section{Limiter Preamp}
-The limiter preamp raises the gain of the audio by the selected amount. The associated
-limiter function works on the resulting louder signal to reduce any peaks to below the
-maximum level. The default selection of 0dB turns all limiter processing off.
-
-The limiter has the effect of reducing dynamic range by amplifying quiet sections while
-loud sections are kept just under maximum gain. This allows listening to the quiet sections
-of dynamic material in noisy environments while preventing sudden loud sections from being
-overbearing.
-
-Think of this as a smart volume control. The preamp in effect turns up the volume by the
-amount you select so that you can hear quiet passages. But it senses when a loud section is
-about to play and quickly and smoothly lowers the volume as necessary to keep the audio
-under the maximum limit. As the loud section fades, the volume is turned back up.
+\section{Compressor}
+The \setting{Compressor} reduces, or compresses, the dynamic range of the audio
+signal. This makes the quieter and louder sections closer to the same volume
+level by progressively reducing the gain of louder signals. When subsequently
+amplified, this has the effect of making the quieter sections louder while
+keeping the louder sections from clipping. This allows listening to the quiet
+sections of dynamic material in noisy environments while preventing sudden loud
+sections from being overbearing.
+
+There are several settings associated with the compressor. The first, and most
+important, is the \setting{Threshold}. The threshold is the audio input level
+at which the compressor begins to act. Any level louder than the threshold
+will be compressed to some extent. The maximum amount of compression, or the
+quietest level at which the compressor will operate, is -24db. The default of
+Off disables the compressor.
+
+The \setting{Makeup Gain} setting has two options: Off and Auto. Off means
+that the compressed audio will not be amplified after compression. The default
+of Auto will amplify the signal so that the loudest possible signal after
+compression will be just under the clipping limit. This is desirable because
+the compressed signal without makeup gain is quieter than the input signal.
+Makeup Gain in Auto restores the signal to the maximum possible level and
+brings the quieter audio up with it. This is what makes it possible to hear
+the quieter audio in noisy environments.
+
+The \setting{Ratio} setting determines how aggressively the compressor reduces
+gain above the threshold. For example, the 2:1 setting means that for each
+two decibels of input signal above the threshold, the compressor will only
+allow the output to appear as one decibel. The higher the ratio, the harder
+the signal is compressed. The ratio setting of Limit means essentially a ratio
+of infinity to one. In this case, the output signal is not allowed to exceed
+the threshold at all.
+
+The \setting{Knee} setting determines how abrupt the transition is from a
+non-compressed signal to a compressed signal. Hard Knee means that the
+transition occurs precisely at the threshold. The Soft Knee setting smoothes
+the transition from plus or minus three decibels around the threshold.
+
+The \setting{Release Time} setting sets the recovery time after the signal is
+compressed. Once the compressor determines that compression is necessary,
+the input signal is reduced appropriately, but the gain isn't allowed to
+immediately return to normal levels. This is necessary to reduce artifacts
+such as "pumping." Instead, the gain is allowed to return to normal at the
+chosen rate. Release Time is the time for the gain to recover by 10dB.
}