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feat: change the compressor unit to apply post-gain instead of pregain.

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Pregaining ran into trouble: could not bring the signal level back to near 0dB. For example, with infinite ratio in the pre-gain system, the signal level was capped at threshold, which in turn ran into trouble with stereo signals.
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vsariola
2021-03-20 17:01:04 +02:00
parent 76cf47a070
commit 42c9e045b7
7 changed files with 15 additions and 20 deletions
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16
templates/amd64-386/effects.asm
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@ -353,18 +353,16 @@ su_op_delay_loop:
; Stereo: push g g on stack, where g is calculated using l^2 + r^2
;-------------------------------------------------------------------------------
{{.Func "su_op_compressor" "Opcode"}}
fdiv dword [{{.Input "compressor" "invgain"}}]; l/g, we'll call this pre inverse gained signal x from now on
fld st0 ; x x
fmul st0, st0 ; x^2 x
{{- if .StereoAndMono "compressor"}}
jnc su_op_compressor_mono
{{- end}}
{{- if .Stereo "compressor"}}
fld st2 ; r x^2 l/g r
fdiv dword [{{.Input "compressor" "invgain"}}]; r/g, we'll call this pre inverse gained signal y from now on
fst st3 ; y x^2 l/g r/g
fmul st0, st0 ; y^2 x^2 l/g r/g
faddp st1, st0 ; y^2+x^2 l/g r/g
fld st2 ; r x^2 l r
fst st3 ; y x^2 l r
fmul st0, st0 ; y^2 x^2 l r
faddp st1, st0 ; y^2+x^2 l r
call su_op_compressor_mono ; So, for stereo, we square both left & right and add them up
fld st0 ; and return the computed gain two times, ready for MULP STEREO
ret
@ -389,9 +387,11 @@ su_op_compressor_mono:
fmul dword [{{.Float 0.5 | .Use}}] ; p=r/2 t*t/l' x
fxch ; t*t/l' p x
fyl2x ; p*log2(t*t/l') x
{{.TailCall "su_power"}} ; 2^(p*log2(t*t/l')) x
; tail call ; Equal to:
{{.Call "su_power"}} ; 2^(p*log2(t*t/l')) x
; Equal to:
; (t*t/l')^p x
; if ratio is at minimum => p=0 => 1 x
; if ratio is at maximum => p=0.5 => t/x => t/x*x=t
fdiv dword [{{.Input "compressor" "invgain"}}]; this used to be pregain but that ran into problems with getting back up to 0 dB so postgain should be better at that
ret
{{- end}}