Source: https://guthlabs.ai/docs/instruments/note-frequency-reference-a4-tuning-offset/implementation/

instrument implementation / implementation-contract

# Note Frequency Reference (A4 Tuning Offset) implementation

A source-bound implementation contract for Note Frequency Reference (A4 Tuning Offset); 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**: t4-085

**Effect**: Computation or source lookup only

## Input and validation requirements

The specification does not state rejection behavior for zero or negative A4 references, producing zero or negative frequencies and undefined cents results. It also leaves the cents comparison reference and sign convention ambiguous; the same 432-Hz tuning can reasonably be reported as either -31.766653633 cents relative to 440-Hz TET or 0 cents relative to its own supplied tuning.

## 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": {
    "note_name": "A4",
    "octave": 4,
    "midi_note": 69,
    "A4_reference_Hz": 440
  },
  "expected_outputs": {
    "frequency_Hz": 440,
    "cents_deviation_from_440_TET": 0
  },
  "working": "n=69, so (n-69)/12=(69-69)/12=0. 2^0=1.  frequency=440*1=440 Hz.  The 440-Hz reference is exactly the 440-Hz 12-TET A4, so cents deviation=1200*log2(440/440)=1200*log2(1)=0 cents."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/note-frequency-reference-a4-tuning-offset/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/note-frequency-reference-a4-tuning-offset/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/note-frequency-reference-a4-tuning-offset/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-tranche4/tranche4-results.json`