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audio-numerics-review

Reviews audio DSP code for numerical correctness. Use when the user asks to review, audit, or check DSP code for correctness issues — filters, feedback loops, fixed-point arithmetic, accumulation loops, or any numeric computation in audio code. Trigger on "check this filter for NaN", "why does my reverb blow up?", "is this numerically stable?", "why do I hear DC in my output?". Pairs with audio-dsp-review (realtime safety); this skill covers numeric correctness. Flag issues proactively.

kunitoki/sonic-skills

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含まれるファイル（2）

SKILL.md3.2 KB
references/numerics-pitfalls.md21.4 KB

SKILL.md（原文）

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Audio Numerics Review

Floating-point is not real math. IEEE 754 edge cases — denormals, NaN propagation, catastrophic cancellation, precision loss — silently produce wrong audio output without crashing. You won't find them with a debugger; you find them by knowing where to look.

Step 1 — Find numeric-critical paths

Locate every function doing floating-point or integer DSP: filter state loops, feedback delay lines, envelope followers, RMS/energy accumulators, pitch detectors, fixed-point paths (CMSIS-DSP, SIMD int16/int32), any division whose denominator may be zero.

Step 2 — Scan for violations

Violation	Where to look	Symptom
Denormal floats	IIR state vars, reverb tanks, delay feedback	Sudden 100× CPU spike when signal decays
NaN / Inf	Divisions, `sqrt`, `acos`/`asin`, peak normalizers	Silence or noise that can't be traced
Catastrophic cancellation	DC-blocking filters, near-Nyquist biquads, first-order diff	Noise floor jumps, loss of precision
Fixed-point overflow	Q15/Q31 multiply, CMSIS paths, SIMD int16	Audible distortion / wrapping
Precision loss	RMS/energy sums, mixing buses, long loops	Accumulated DC offset, incorrect levels
FTZ/DAZ absent	`prepareToPlay`/stream-open — no mode setup	Denormals hit on some hosts but not others

For code examples and platform-specific notes see references/numerics-pitfalls.md.

Step 3 — Write the review

## Audio Numerics Review: `[file / function]`

### Verdict
[Safe | Has critical violations | Warnings only] — one sentence summary

### Critical Violations
**[Category]: [description]**
`file:line` — `offending code`
Why: one sentence on the numeric risk
Fix: concrete suggestion

### Warnings
[same format]

### What's Done Well
[guarded divisions, double accumulators, FTZ setup, etc.]

### Recommended Fixes (priority order)
1. ...

Quick fix table

Violation	Safe alternative
Denormal in feedback	`ScopedNoDenormals`; FTZ+DAZ in `prepareToPlay`; DC-offset clamp
Division by zero	`(denom > 1e-6f) ? num/denom : fallback`
`sqrt`/`acos`/`asin` unclamped	`std::sqrt(std::max(0.f, x))`, `std::clamp` inputs
NaN propagating silently	`assert(!std::isnan(y))` in debug; validate at entry points
Cancellation in coefficients	Compute coefficients in `double`; use numerically stable forms
Fixed-point overflow	Promote to wider type before multiply; `__SSAT`, CMSIS saturating ops
Precision loss in long sum	`double` accumulator or Kahan compensated summation
FTZ/DAZ absent	Set explicitly in `prepareToPlay`; use `ScopedNoDenormals` per-block

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概要と使いどころ

au-review

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Reviews AudioUnit v2/v3 plugin implementations for spec compliance, thread safety, and correctness. Use when the user asks to review an AudioUnit plugin, check an AUv3 app extension, audit property or parameter handling, or asks "is my AUComponent thread-safe?" or "why does my AU crash in Logic?". Trigger on phrases like "review my AudioUnit", "check my AUv3", "is my render block safe?", or when you see AURenderCallback, internalRenderBlock, kAudioUnitProperty_*, or AUAudioUnit in the code.

日本語の概要は準備中です。原文の説明を表示しています。