How Real-Time Pitch Correction and Auto-Tune Technology Works
A method for detecting the pitch of a musical note and adjusting it to a target frequency in real time using auto-correlation.
Original patent title: “Pitch detection and intonation correction apparatus and method”
A method for detecting the pitch of a musical note and adjusting it to a target frequency in real time using auto-correlation. Granted to Auburn Audio Technologies Inc in 1999 with 42 claims and 39 forward citations, and it is now in the public domain.
Key facts
Coverage
What does this patent actually cover?
This patent describes a digital signal processing method that identifies the fundamental frequency of a voice or instrument by sampling audio and calculating its period. It uses an auto-correlation function—a mathematical way to find repeating patterns in a signal—to determine the pitch. Once the pitch is identified, the system calculates the difference between the current note and a target note from a musical scale or MIDI input. It then resamples the audio waveform to shift its frequency, effectively correcting the intonation of the performance.
The gap
What does this patent NOT cover?
- Does not cover non-digital or analog-only pitch correction methods.
- Does not cover methods that rely on frequency domain analysis like Fast Fourier Transforms (FFT).
- Does not cover non-real-time pitch correction performed on pre-recorded audio files.
- Does not cover vocal synthesis or generating new notes from scratch.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
What made this novel
The invention uses a recursive update formula for energy and correlation functions (E and H) that allows the system to find the pitch period within just two cycles of the waveform, enabling the low-latency performance required for live audio.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Auto-Tune software plugins
Live vocal pitch correction processors
Digital audio workstation (DAW) pitch correction tools
Why it matters
The bigger picture
This technology is the technical foundation for modern pitch-correction tools, commonly known as Auto-Tune. By enabling real-time correction, it allowed performers to maintain perfect intonation during live concerts and studio sessions. It fundamentally changed the sound of popular music by making precise pitch control a standard production element.
Filed
October 15, 1998
Granted
October 26, 1999
Market context
Who's building on this
Companies in this space
Companies like Antares Audio Technologies, Celemony, and Waves Audio have built extensive product ecosystems based on these fundamental principles of real-time pitch detection and manipulation. The industry has since evolved to include more sophisticated spectral analysis, but the core concept of period-based resampling remains a staple in audio engineering.
Market impact
This patent helped standardize the use of pitch correction in professional music production, turning a niche studio tool into a ubiquitous feature of modern recording. It triggered a shift in aesthetic expectations for vocal performance and enabled the 'robotic' vocal effect that became a defining sound in many genres of contemporary music.
Claim 1 — Plain English
What this patent covers
This patent describes a digital signal processing method that identifies the fundamental frequency of a voice or instrument by sampling audio and calculating its period. It uses an auto-correlation function—a mathematical way to find repeating patterns in a signal—to determine the pitch. Once the pitch is identified, the system calculates the difference between the current note and a target note from a musical scale or MIDI input. It then resamples the audio waveform to shift its frequency, effectively correcting the intonation of the performance.
The clever bit
The invention uses a recursive update formula for energy and correlation functions (E and H) that allows the system to find the pitch period within just two cycles of the waveform, enabling the low-latency performance required for live audio.
What it does not cover
- Does not cover non-digital or analog-only pitch correction methods.
- Does not cover methods that rely on frequency domain analysis like Fast Fourier Transforms (FFT).
- Does not cover non-real-time pitch correction performed on pre-recorded audio files.
- Does not cover vocal synthesis or generating new notes from scratch.
Patent Journey
From filing to expiry
PatentBrief Score
Impact Score
Moderate
Citation count
32/40
Moderately cited
Claim breadth
20/20
Very broad protection
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$32K – $104K
Midpoint $65K · expired or expiring · industry ×1.5
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
The original legal language
Original claims
42 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Hildebrand, H. A. (1999). How Real-Time Pitch Correction and Auto-Tune Technology Works (U.S. Patent No. 5,973,252). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/5973252/auto-tune-pitch-correction
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How Real-Time Pitch Correction and Auto-Tune Technology Works cover?
A method for detecting the pitch of a musical note and adjusting it to a target frequency in real time using auto-correlation.
Who owns patent US 5973252?
Auburn Audio Technologies Inc owns this patent, granted in 1999.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 5973252 cited by?
This patent has been cited by 39 later patents that build on its ideas.
What problem does this patent solve?
This technology is the technical foundation for modern pitch-correction tools, commonly known as Auto-Tune. By enabling real-time correction, it allowed performers to maintain perfect intonation during live concerts and studio sessions. It fundamentally changed the sound of popular music by making precise pitch control a standard production element.
What does this patent NOT cover?
Does not cover non-digital or analog-only pitch correction methods.
Patent monitoring