From 95e2d72759543b739a8faba7545fe6d9752fb4ef Mon Sep 17 00:00:00 2001 From: Jeffrey Goode Date: Wed, 4 Nov 2009 18:14:36 +0000 Subject: 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 --- manual/configure_rockbox/sound_settings.tex | 58 ++++++++++++++++++++++------- 1 file changed, 44 insertions(+), 14 deletions(-) (limited to 'manual') 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. } -- cgit v1.2.3