An oil-industry pitch algorithm was patented as a vocal corrector

US patent 5,973,252 documents the pitch-correction method behind Auto-Tune, traced by its maker to geophysical signal analysis.

Historical event

October 27, 1997

First source published

October 26, 1999

Site publication

September 18, 2026

What happened

On 27 October 1997, an application was filed for what became US Patent 5,973,252, 'Pitch detection and intonation correction apparatus and method', assigned to Auburn Audio Technologies Inc and naming Harold A. Hildebrand as inventor. Hildebrand is better known professionally as Andy Hildebrand, and Auburn Audio Technologies became Antares Audio Technologies, the company that has sold the product commercially as Auto-Tune since 1997. The company's own account of its history says Hildebrand trained as a flutist and worked as a signal-processing engineer in the oil industry, and that the correction method grew out of his work reading seismic data to locate underground deposits. The patent itself was granted on 26 October 1999.

What the documents say

The patent's own abstract describes a device that determines the pitch of a note from a voice or instrument using an autocorrelation function of the waveform, compares the detected period to a desired period drawn from a musical scale, and resamples the signal by that ratio, smoothing the ratio over time 'to remove instantaneous output pitch changes'. That smoothing step is the mechanism that separates a corrective tool from an audibly robotic effect. Antares's own history page adds the origin story the patent does not: the underlying autocorrelation approach came from techniques for reading seismic waveforms, repurposed to track a sung pitch instead of a rock layer. The same page dates the product's move from correction tool to audible effect, crediting Cher's 1998 single 'Believe' with introducing what it calls the 'AutoTune Effect' to a mainstream audience, a use the patent's own language does not describe.

Why it matters for makers

The distinction the patent draws, between detecting a period and resampling toward a target period, is the same distinction that separates 'corrected' from 'stylised' today. A vocal take with the smoothing set high reads as in tune without an audible artefact; the same detector with smoothing reduced produces the stepped, glassy sound used as a deliberate effect. Knowing both are the same underlying mechanism, tuned differently, is more useful than treating 'Auto-Tune' as a single fixed sound.

What to check before you use it

A producer working with any real-time pitch corrector can usefully ask what a tool's own documentation says about its correction speed and scale-quantisation settings, since the 1999 patent describes these as governing transparent versus audible correction. This is an editorial reading of the patent's own language, not a claim about how any current plugin is built.

• Is the correction speed set to preserve natural pitch drift, or to remove it entirely?
• Does the scale or key setting match the actual key of the take, including any modulation?
• If the audible effect is the goal, is that a deliberate creative choice, not an accident of default settings?

A patent granted in 1999 for correcting intonation is not a licence for any specific plugin's sound today, but its claims still describe the mechanism most pitch tools share: detect a period, compare it to a target, resample, and decide how quickly to get there.

Sources & reading trail

Gives the patent's abstract, inventor, assignee, priority/filing date and grant date, and describes the autocorrelation-based pitch detection and resampling method.

Source published: 26 October 1999 · Retrieved: 16 September 2026

Company's own account of Hildebrand's oil-industry seismic-signal background, the 1997 product launch, and the 1998 Cher 'Believe' effect.

Source published: Not established · Retrieved: 16 September 2026

Papers, terms and official documents establish the record; the maker reading and the checks are Signal to Song editorial analysis. This retrospective draft does not imply the site published on the event date.

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Published September 18, 2026, not on the date of the event described.