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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.
This commit is contained in:
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}}

12
templates/wasm/effects.wat
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@ -409,10 +409,6 @@
;; Stereo: push g g on stack, where g is calculated using l^2 + r^2
;;-------------------------------------------------------------------------------
(func $su_op_compressor (param $stereo i32) (local $x2 f32) (local $level f32) (local $t2 f32)
(call $push (f32.div ;; the inverse gain is applied on this signal, even if the gain is side-chained somewhere else
(call $pop)
(call $input (i32.const {{.InputNumber "compressor" "invgain"}}))
))
{{- if .Stereo "compressor"}}
(local.set $x2 (f32.mul
(call $peek)
@ -420,10 +416,6 @@
))
(if (local.get $stereo)(then
(call $pop)
(call $push (f32.div
(call $pop)
(call $input (i32.const {{.InputNumber "compressor" "invgain"}}))
))
(local.set $x2 (f32.add
(local.get $x2)
(f32.mul
@ -472,6 +464,10 @@
)(else
(call $push (f32.const 1)) ;; unity gain if we are below threshold
))
(call $push (f32.div ;; apply post-gain ("make up gain")
(call $pop)
(call $input (i32.const {{.InputNumber "compressor" "invgain"}}))
))
{{- if .Stereo "compressor"}}
(if (local.get $stereo)(then
(call $push (call $peek))