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fix: SF2 mode filter is too muffled

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minjaesong
2026-06-14 11:17:35 +09:00
parent 2e9b380843
commit aa9ea2eeca
2 changed files with 102 additions and 24 deletions
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119
tsvm_core/src/net/torvald/tsvm/peripheral/AudioAdapter.kt
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@@ -18,6 +18,7 @@ import kotlin.math.roundToInt
import kotlin.math.PI
import kotlin.math.cos
import kotlin.math.sin
import kotlin.math.sqrt
import kotlin.math.exp
private class RenderRunnable(val playhead: AudioAdapter.Playhead) : Runnable {
@@ -1840,6 +1841,15 @@ class AudioAdapter(val vm: VM) : PeriBase(VM.PERITYPE_SOUND) {
* B0 = (d + 2e) / denom
* B1 = −e / denom
* y[n] = A0 × x[n] + B0 × y[n−1] + B1 × y[n−2]
*
* SoundFont mode uses a different, faithful port of FluidSynth's filter
* (reference_materials/fluidsynth/src/rvoice/fluid_iir_filter_impl.cpp):
* the RBJ biquad low-pass with the SF2 `sqrt(1/Q)` resonance gain-norm.
* The IT all-pole filter is overdamped — even at the SF2 "open" default
* (13500 cents) it loses ~3 dB at 8 kHz / ~5 dB at 12 kHz, which is audible
* muffling against FluidSynth on every default-filter GM instrument. The
* biquad's passband is maximally flat (Butterworth at the default Q), so
* SF mode now switches topology rather than just remapping cutoff/Q.
*/
private fun refreshVoiceFilter(voice: Voice) {
val cut = voice.currentCutoff
@@ -1849,27 +1859,46 @@ class AudioAdapter(val vm: VM) : PeriBase(VM.PERITYPE_SOUND) {
voice.filterResonanceCached = res
val nyquist = SAMPLING_RATE * 0.5 - 1.0
val frequency: Double
val dmpfac: Double
// println("voice.filterSfMode = ${voice.filterSfMode}")
if (voice.filterSfMode) {
// SoundFont mode: cutoff = absolute cents, resonance = centibels above DC gain.
// freq = 8.176 Hz × 2^(cents/1200) (cents are relative to 8.176 Hz = MIDI 0)
// SF2 Q is the resonant-peak height in dB×10. For this IT-style 2-pole IIR the
// peak gain ≈ −20·log10(dmpfac) dB, so dmpfac = 10^(−dB/20) = 10^(−Qcb/200).
// freq = 8.176 Hz × 2^(cents/1200) (cents relative to 8.176 Hz = MIDI 0)
// FluidSynth clamps fres to [5 Hz, 0.45·fs] and uses it as an anti-alias
// filter rather than switching off near Nyquist (fluid_iir_filter_calc).
if (cut >= 0xFFFF) { voice.filterActive = false; return }
frequency = (8.176 * 2.0.pow(cut / 1200.0)).coerceIn(1.0, nyquist)
val fres = (8.176 * 2.0.pow(cut / 1200.0)).coerceIn(5.0, 0.45 * SAMPLING_RATE)
// SF2 Q (centibels) → linear Q, with FluidSynth's −3.01 dB offset so that
// Q=0 cB is Butterworth (q_lin = 1/√2), i.e. no resonance hump
// (fluid_iir_filter_q_from_dB). Clamp dB to [0, 96] as FluidSynth does.
val qcb = if (res >= 0xFFFF) 0 else res
// Clamp to the IT filter's max resonance (≈24 dB) to keep the IIR stable / unclipped.
dmpfac = 10.0.pow(-qcb / 200.0).coerceIn(0.0625, 1.0)
} else {
if (cut.coerceIn(0, 255) >= 255) { voice.filterActive = false; return }
val itCutoff = cut.coerceIn(0, 254) * 0.5 // 0..127
val itResonance = if (res >= 255) 0.0 else res.coerceIn(0, 254) * 0.5
frequency = (110.0 * 2.0.pow(itCutoff / 24.0 + 0.25)).coerceAtMost(nyquist)
dmpfac = 10.0.pow(-itResonance * (24.0 / 128.0) / 20.0)
val qDb = (qcb / 10.0).coerceIn(0.0, 96.0) - 3.01
val qLin = 10.0.pow(qDb / 20.0).coerceAtLeast(0.001)
// RBJ cookbook low-pass (bilinear-transformed), normalised to a0.
val omega = 2.0 * PI * fres / SAMPLING_RATE
val sinC = sin(omega)
val cosC = cos(omega)
val alpha = sinC / (2.0 * qLin)
val a0inv = 1.0 / (1.0 + alpha)
// SF2 §2.01 p.59: halve the resonance-peak height by scaling the gain
// with sqrt(1/Q); folded into the b coefficients here.
val gain = a0inv / sqrt(qLin)
voice.filterBqB1 = (1.0 - cosC) * gain
voice.filterBqB02 = voice.filterBqB1 * 0.5
voice.filterBqA1 = -2.0 * cosC * a0inv
voice.filterBqA2 = (1.0 - alpha) * a0inv
voice.filterIsBiquad = true
voice.filterActive = true
return
}
if (cut.coerceIn(0, 255) >= 255) { voice.filterActive = false; return }
val itCutoff = cut.coerceIn(0, 254) * 0.5 // 0..127
val itResonance = if (res >= 255) 0.0 else res.coerceIn(0, 254) * 0.5
val frequency = (110.0 * 2.0.pow(itCutoff / 24.0 + 0.25)).coerceAtMost(nyquist)
val dmpfac = 10.0.pow(-itResonance * (24.0 / 128.0) / 20.0)
val r = SAMPLING_RATE / (2.0 * PI * frequency)
val d = dmpfac * r + dmpfac - 1.0
val e = r * r
@@ -1878,15 +1907,33 @@ class AudioAdapter(val vm: VM) : PeriBase(VM.PERITYPE_SOUND) {
voice.filterA0 = 1.0 / denom
voice.filterB0 = (d + e + e) / denom
voice.filterB1 = -e / denom
voice.filterIsBiquad = false
voice.filterActive = true
}
/** Apply the cached IT-style 2-pole LPF to one mono sample. Caller must
* have called refreshVoiceFilter at the start of the tick. The history
* taps are clipped to ±2.0 to tame resonance ringing on extreme settings,
* matching OpenMPT's ClipFilter helper. */
/** Apply the cached voice low-pass to one mono sample. Caller must have
* called refreshVoiceFilter at the start of the tick.
*
* SoundFont voices run FluidSynth's RBJ biquad (Direct Form I):
* y[n] = b02·(x[n]+x[n-2]) + b1·x[n-1] - a1·y[n-1] - a2·y[n-2]
*
* Tracker voices run the IT all-pole recurrence, whose history taps are
* clipped to ±2.0 to tame resonance ringing on extreme settings (matching
* OpenMPT's ClipFilter helper). The biquad does not clip — FluidSynth runs
* it unclamped, and the SF2 gain-norm already bounds the resonance peak. */
private fun applyVoiceFilter(voice: Voice, x0: Double): Double {
if (!voice.filterActive) return x0
if (voice.filterIsBiquad) {
val y0 = voice.filterBqB02 * (x0 + voice.filterX2) +
voice.filterBqB1 * voice.filterX1 -
voice.filterBqA1 * voice.filterY1 -
voice.filterBqA2 * voice.filterY2
voice.filterX2 = voice.filterX1
voice.filterX1 = x0
voice.filterY2 = voice.filterY1
voice.filterY1 = y0
return y0
}
val y1Clipped = voice.filterY1.coerceIn(-2.0, 2.0)
val y2Clipped = voice.filterY2.coerceIn(-2.0, 2.0)
val y0 = voice.filterA0 * x0 +
@@ -2381,7 +2428,7 @@ class AudioAdapter(val vm: VM) : PeriBase(VM.PERITYPE_SOUND) {
// 255 = filter off (IT high-bit-clear); 0..254 = active range matching IT 0..127 at double resolution.
voice.currentCutoff = voice.activeDefaultCutoff
voice.currentResonance = voice.activeDefaultResonance
voice.filterY1 = 0.0; voice.filterY2 = 0.0
voice.filterY1 = 0.0; voice.filterY2 = 0.0; voice.filterX1 = 0.0; voice.filterX2 = 0.0
voice.filterCutoffCached = -1 // force coefficient refresh on first tick
voice.filterResonanceCached = -1
voice.noteVal = noteVal
@@ -2569,6 +2616,13 @@ class AudioAdapter(val vm: VM) : PeriBase(VM.PERITYPE_SOUND) {
v.filterB1 = src.filterB1
v.filterY1 = src.filterY1
v.filterY2 = src.filterY2
v.filterIsBiquad = src.filterIsBiquad
v.filterBqB02 = src.filterBqB02
v.filterBqB1 = src.filterBqB1
v.filterBqA1 = src.filterBqA1
v.filterBqA2 = src.filterBqA2
v.filterX1 = src.filterX1
v.filterX2 = src.filterX2
v.filterCutoffCached = src.filterCutoffCached
v.filterResonanceCached = src.filterResonanceCached
v.randomVolBias = src.randomVolBias
@@ -3509,7 +3563,7 @@ class AudioAdapter(val vm: VM) : PeriBase(VM.PERITYPE_SOUND) {
voice.fadeoutVolume = 1.0
voice.autoVibPhase = 0
voice.autoVibTicksSinceTrigger = 0
voice.filterY1 = 0.0; voice.filterY2 = 0.0
voice.filterY1 = 0.0; voice.filterY2 = 0.0; voice.filterX1 = 0.0; voice.filterX2 = 0.0
voice.noteVolume = applyRetrigVolMod(voice.noteVolume, voice.retrigVolMod)
voice.rowVolume = voice.noteVolume
}
@@ -3665,9 +3719,16 @@ class AudioAdapter(val vm: VM) : PeriBase(VM.PERITYPE_SOUND) {
val finalPitch = (bg.noteVal + autoVibDelta + pitchEnvDelta).coerceIn(0x20, 0xFFFF)
bg.playbackRate = computePlaybackRate(bg, finalPitch)
// Filter envelope: same scaling rule as foreground, using the active cutoff.
// Must branch on SF mode too — an SF-mode ghost's cutoff is in cents (0..0xFFFF),
// so the IT 0..254 clamp would otherwise collapse it to ~9 Hz (total muffling).
if (bg.hasFilterEnv && bg.pfEnvOn) {
val baseCut = if (bg.activeDefaultCutoff < 255) bg.activeDefaultCutoff else 254
bg.currentCutoff = (baseCut * bg.envFilterValue).toInt().coerceIn(0, 254)
if (bg.filterSfMode) {
val baseCut = if (bg.activeDefaultCutoff < 0xFFFF) bg.activeDefaultCutoff else 13500
bg.currentCutoff = (baseCut * bg.envFilterValue).toInt().coerceIn(0, 0xFFFF)
} else {
val baseCut = if (bg.activeDefaultCutoff < 255) bg.activeDefaultCutoff else 254
bg.currentCutoff = (baseCut * bg.envFilterValue).toInt().coerceIn(0, 254)
}
}
refreshVoiceFilter(bg)
// Reap fully-faded ghosts so the pool stays drained.
@@ -4249,6 +4310,18 @@ class AudioAdapter(val vm: VM) : PeriBase(VM.PERITYPE_SOUND) {
var filterB1 = 0.0
var filterY1 = 0.0
var filterY2 = 0.0
// SoundFont mode uses a proper RBJ biquad low-pass (matching FluidSynth's
// fluid_iir_filter, not the IT all-pole topology — see refreshVoiceFilter).
// When true, applyVoiceFilter runs the biquad recurrence:
// y[n] = b02·(x[n]+x[n-2]) + b1·x[n-1] - a1·y[n-1] - a2·y[n-2]
// sharing filterY1/Y2 as the output history and adding x[n-1]/x[n-2].
var filterIsBiquad = false
var filterBqB02 = 0.0
var filterBqB1 = 0.0
var filterBqA1 = 0.0
var filterBqA2 = 0.0
var filterX1 = 0.0
var filterX2 = 0.0
// Snapshot of cutoff/resonance the cached coefficients correspond to.
var filterCutoffCached = -1
var filterResonanceCached = -1
@@ -4626,7 +4699,7 @@ class AudioAdapter(val vm: VM) : PeriBase(VM.PERITYPE_SOUND) {
it.noteVal = 0x0000; it.basePitch = 0x4000
it.amigaPeriod = -1.0; it.linearFreq = -1.0
it.tonePortaTarget = -1; it.tonePortaSpeed = 0
it.filterY1 = 0.0; it.filterY2 = 0.0
it.filterY1 = 0.0; it.filterY2 = 0.0; it.filterX1 = 0.0; it.filterX2 = 0.0
it.filterCutoffCached = -1; it.filterResonanceCached = -1
it.currentCutoff = 0xFF; it.currentResonance = 0xFF
it.nesDpcmCounter = 63