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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.

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kunitoki/sonic-skills

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包含的文件（2）

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

SKILL.md（原文）

安装前可以查看交给 AI 代理的指令内容。

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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