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author | Jeffrey Goode <jeffg7@gmail.com> | 2009-11-04 18:14:36 +0000 |
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committer | Jeffrey Goode <jeffg7@gmail.com> | 2009-11-04 18:14:36 +0000 |
commit | 95e2d72759543b739a8faba7545fe6d9752fb4ef (patch) | |
tree | f8afc86797e83fd4556ec17e857d4caa097d3bb9 /manual/configure_rockbox/sound_settings.tex | |
parent | a06feaa7ecb010e6a6d85f49e6392f06f9f814a2 (diff) | |
download | rockbox-95e2d72759543b739a8faba7545fe6d9752fb4ef.tar.gz rockbox-95e2d72759543b739a8faba7545fe6d9752fb4ef.zip |
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.tex | 58 |
1 files changed, 44 insertions, 14 deletions
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. | |||
445 | } | 445 | } |
446 | 446 | ||
447 | \opt{swcodec}{ | 447 | \opt{swcodec}{ |
448 | \section{Limiter Preamp} | 448 | \section{Compressor} |
449 | The limiter preamp raises the gain of the audio by the selected amount. The associated | 449 | The \setting{Compressor} reduces, or compresses, the dynamic range of the audio |
450 | limiter function works on the resulting louder signal to reduce any peaks to below the | 450 | signal. This makes the quieter and louder sections closer to the same volume |
451 | maximum level. The default selection of 0dB turns all limiter processing off. | 451 | level by progressively reducing the gain of louder signals. When subsequently |
452 | 452 | amplified, this has the effect of making the quieter sections louder while | |
453 | The limiter has the effect of reducing dynamic range by amplifying quiet sections while | 453 | keeping the louder sections from clipping. This allows listening to the quiet |
454 | loud sections are kept just under maximum gain. This allows listening to the quiet sections | 454 | sections of dynamic material in noisy environments while preventing sudden loud |
455 | of dynamic material in noisy environments while preventing sudden loud sections from being | 455 | sections from being overbearing. |
456 | overbearing. | 456 | |
457 | 457 | There are several settings associated with the compressor. The first, and most | |
458 | Think of this as a smart volume control. The preamp in effect turns up the volume by the | 458 | important, is the \setting{Threshold}. The threshold is the audio input level |
459 | amount you select so that you can hear quiet passages. But it senses when a loud section is | 459 | at which the compressor begins to act. Any level louder than the threshold |
460 | about to play and quickly and smoothly lowers the volume as necessary to keep the audio | 460 | will be compressed to some extent. The maximum amount of compression, or the |
461 | under the maximum limit. As the loud section fades, the volume is turned back up. | 461 | quietest level at which the compressor will operate, is -24db. The default of |
462 | Off disables the compressor. | ||
463 | |||
464 | The \setting{Makeup Gain} setting has two options: Off and Auto. Off means | ||
465 | that the compressed audio will not be amplified after compression. The default | ||
466 | of Auto will amplify the signal so that the loudest possible signal after | ||
467 | compression will be just under the clipping limit. This is desirable because | ||
468 | the compressed signal without makeup gain is quieter than the input signal. | ||
469 | Makeup Gain in Auto restores the signal to the maximum possible level and | ||
470 | brings the quieter audio up with it. This is what makes it possible to hear | ||
471 | the quieter audio in noisy environments. | ||
472 | |||
473 | The \setting{Ratio} setting determines how aggressively the compressor reduces | ||
474 | gain above the threshold. For example, the 2:1 setting means that for each | ||
475 | two decibels of input signal above the threshold, the compressor will only | ||
476 | allow the output to appear as one decibel. The higher the ratio, the harder | ||
477 | the signal is compressed. The ratio setting of Limit means essentially a ratio | ||
478 | of infinity to one. In this case, the output signal is not allowed to exceed | ||
479 | the threshold at all. | ||
480 | |||
481 | The \setting{Knee} setting determines how abrupt the transition is from a | ||
482 | non-compressed signal to a compressed signal. Hard Knee means that the | ||
483 | transition occurs precisely at the threshold. The Soft Knee setting smoothes | ||
484 | the transition from plus or minus three decibels around the threshold. | ||
485 | |||
486 | The \setting{Release Time} setting sets the recovery time after the signal is | ||
487 | compressed. Once the compressor determines that compression is necessary, | ||
488 | the input signal is reduced appropriately, but the gain isn't allowed to | ||
489 | immediately return to normal levels. This is necessary to reduce artifacts | ||
490 | such as "pumping." Instead, the gain is allowed to return to normal at the | ||
491 | chosen rate. Release Time is the time for the gain to recover by 10dB. | ||
462 | } | 492 | } |