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 --- lib/rbcodec/dsp/compressor.h | 1 + 1 file changed, 1 insertion(+) (limited to 'lib/rbcodec/dsp/compressor.h') diff --git a/lib/rbcodec/dsp/compressor.h b/lib/rbcodec/dsp/compressor.h index e41950926e..35aa0eeb65 100644 --- a/lib/rbcodec/dsp/compressor.h +++ b/lib/rbcodec/dsp/compressor.h @@ -28,6 +28,7 @@ struct compressor_settings int ratio; int knee; int release_time; + int attack_time; }; void dsp_set_compressor(const struct compressor_settings *settings); -- cgit v1.2.3