Source: https://guthlabs.ai/docs/instruments/semitone-cents-ratio-playback-speed-pitch-time-calculator/implementation/

instrument implementation / implementation-contract

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

A source-bound implementation contract for Semitone/Cents Ratio ↔ Playback Speed (Pitch/Time) Calculator; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## 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

[01**Overview**](<https://guthlabs.ai/docs/instruments/semitone-cents-ratio-playback-speed-pitch-time-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/semitone-cents-ratio-playback-speed-pitch-time-calculator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/semitone-cents-ratio-playback-speed-pitch-time-calculator/qualification/>)

## 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`