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TAD: pre/de-emphasis

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minjaesong
2025-11-07 15:16:35 +09:00
parent e743fbf3c0
commit 8878d37e5b
3 changed files with 142 additions and 1 deletions
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46
tsvm_core/src/net/torvald/tsvm/peripheral/AudioAdapter.kt
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@@ -160,6 +160,12 @@ class AudioAdapter(val vm: VM) : PeriBase(VM.PERITYPE_SOUND) {
// Dither state for noise shaping (2 channels, 2 history samples each)
private val ditherError = Array(2) { FloatArray(2) }
// De-emphasis filter state (persistent across chunks to prevent discontinuities)
private var deemphPrevXL = 0.0f
private var deemphPrevYL = 0.0f
private var deemphPrevXR = 0.0f
private var deemphPrevYR = 0.0f
private val renderRunnables: Array<RenderRunnable>
private val renderThreads: Array<Thread>
private val writeQueueingRunnables: Array<WriteQueueingRunnable>
@@ -422,6 +428,43 @@ class AudioAdapter(val vm: VM) : PeriBase(VM.PERITYPE_SOUND) {
}
}
//=============================================================================
// De-emphasis Filter
//=============================================================================
private fun calculateDeemphasisCoeffs(): Triple<Float, Float, Float> {
// De-emphasis factor
val alpha = 0.5f
val b0 = 1.0f
val b1 = 0.0f // No feedforward delay
val a1 = -alpha // NEGATIVE because equation has minus sign: y = x - a1*prev_y
return Triple(b0, b1, a1)
}
private fun applyDeemphasis(left: FloatArray, right: FloatArray, count: Int) {
val (b0, b1, a1) = calculateDeemphasisCoeffs()
// Left channel - use instance state variables (persistent across chunks)
for (i in 0 until count) {
val x = left[i]
val y = b0 * x + b1 * deemphPrevXL - a1 * deemphPrevYL
left[i] = y
deemphPrevXL = x
deemphPrevYL = y
}
// Right channel - use instance state variables (persistent across chunks)
for (i in 0 until count) {
val x = right[i]
val y = b0 * x + b1 * deemphPrevXR - a1 * deemphPrevYR
right[i] = y
deemphPrevXR = x
deemphPrevYR = y
}
}
// M/S stereo correlation (no dithering - that's now in spectral interpolation)
private fun msCorrelate(mid: FloatArray, side: FloatArray, left: FloatArray, right: FloatArray, sampleCount: Int) {
for (i in 0 until sampleCount) {
@@ -526,6 +569,9 @@ class AudioAdapter(val vm: VM) : PeriBase(VM.PERITYPE_SOUND) {
// Expand dynamic range (gamma expansion)
expandGamma(pcm32Left, pcm32Right, sampleCount)
// Apply de-emphasis filter (AFTER gamma expansion, BEFORE PCM32f to PCM8)
applyDeemphasis(pcm32Left, pcm32Right, sampleCount)
// Dither to 8-bit PCMu8
pcm32fToPcm8(pcm32Left, pcm32Right, sampleCount)