From d0918b98fa0cfba21208a4fb5ed153687b8f02c3 Mon Sep 17 00:00:00 2001 From: Ryan Billing Date: Fri, 4 Oct 2013 01:57:00 +1300 Subject: DSP Compressor: Sidechain, Exponential Atk/Rls This is an improvement to the current compressor which I have added to my own Sansa Fuze V2 build. I am submitting here in case others find it interesting. Features added to the existing compressor: Attack, Look-ahead, Sidechain Filtering. Exponential attack and release characteristic response. Benefits from adding missing features: Attack: Preserve perceived "brightness" of tone by letting onset transients come through at a higher level than the rest of the compressed program material. Look-ahead: With Attack comes clipping on the leading several cycles of a transient onset. With look-ahead function, this can be pre-emptively mitigated with a slower gain change (less distortion). Look-ahead limiting is implemented to prevent clipping while keeping gain change ramp to an interval near 3ms instead of instant attack. The existing compressor implementation distorts the leading edge of a transient by causing instant gain change, resulting in log() distortion. This sounds "woofy" to me. Exponential Attack/Release: eMore natural sounding. On attack, this is a true straight line of 10dB per attack interval. Release is a little different, however, sounds natural as an analog compressor. Sidechain Filtering: Mild high-pass filter reduces response to low frequency onsets. For example, a hard kick drum is less likely to make the whole of the program material appear to fade in and out. Combined with a moderate attack time, such a transient will ride through with minimal audible artifact. Overall these changes make dynamic music sound more "open", more natural. The goal of a compressor is to make dyanamic music sound louder without necessarily sounding as though it has been compressed. I believe these changes come closer to this goal. Enjoy. If not, I am enjoying it Change-Id: I664eace546c364b815b4dc9ed4a72849231a0eb2 Reviewed-on: http://gerrit.rockbox.org/626 Tested: Purling Nayuki Reviewed-by: Michael Giacomelli --- manual/configure_rockbox/sound_settings.tex | 3 +++ 1 file changed, 3 insertions(+) (limited to 'manual/configure_rockbox/sound_settings.tex') diff --git a/manual/configure_rockbox/sound_settings.tex b/manual/configure_rockbox/sound_settings.tex index f06bfaf6e5..d2da07b983 100644 --- a/manual/configure_rockbox/sound_settings.tex +++ b/manual/configure_rockbox/sound_settings.tex @@ -603,6 +603,9 @@ 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{Attack Time} setting sets the delay in milliseconds between the +input signal exceeding the activation threshold and acting upon it. + 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 -- cgit v1.2.3