Semitone/Cents Ratio ↔ Playback Speed (Pitch/Time) Calculator implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-clean

Evidence ID

t5-124

Effect

Computation or source lookup only

Input and validation requirements

A speed input of -100% produces speedRatio = 0, making the inverse logarithm undefined. The instrument must reject this input or explicitly report an undefined semitone shift.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "semitone_shift": 0,
    "source_bpm": 120
  },
  "expected_outputs": {
    "speed_ratio": 1,
    "speed_percentage": 0,
    "resulting_bpm": 120
  },
  "working": "speedRatio=2^(0/12)=2^0=1. speedPercentage=(1-1)*100=0%. resultingBPM=120*1=120 BPM."
}

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche5/tranche5-results.json