# 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. - **Patent:** US 5973252 - **Original title:** Pitch detection and intonation correction apparatus and method - **Owner:** Auburn Audio Technologies Inc - **Granted:** 1999 - **Status:** Public domain (expired) - **Times cited:** 39 - **Field:** consumer_electronics, software ## What it does 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. ## 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. ## 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. ## Real-world examples 1. Auto-Tune software plugins 2. Live vocal pitch correction processors 3. Digital audio workstation (DAW) pitch correction tools ## Why it matters 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. ## 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. **Full plain-English explainer:** https://patentbrief.org/patent/us/5973252/auto-tune-pitch-correction **Original patent:** https://patents.google.com/patent/US5973252 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How to Automatically Generate Musical Harmonies from Audio](https://patentbrief.org/patent/us/8168877/musical-harmony-generation-from-polyphonic-audio-signals) — This 2012 patent describes a system that listens to music and automatically generates harmony notes to accompany a melody, even detecting and ignoring accidental strums on stringed instruments. - [How Touchscreens Precisely Align Signals to Detect Your Touch](https://patentbrief.org/patent/us/8493330/individual-channel-phase-delay-scheme) — Apple's patent describes a way for touchscreens to adjust the timing of internal electrical signals so they perfectly match the signals coming from your finger, making touch detection more accurate. - [How Digital Audio Compression Works](https://patentbrief.org/patent/us/5579430/digital-encoding-process) — A foundational method for compressing digital audio by transforming sound into spectral data and using variable-length codes to store it efficiently. - [How the Theremin Makes Music Without Touching Anything](https://patentbrief.org/patent/us/1661058/theremin-leon-theremin) — Leon Theremin's 1928 patent for an electronic musical instrument that generates sound based on the proximity of a performer's hands to metal antennas. - [How Leo Fender's Tremolo Bridge Changes Guitar Pitch](https://patentbrief.org/patent/us/2741146/fender-stratocaster-tremolo) — A mechanical bridge system for electric guitars that allows players to temporarily change the tension and pitch of all strings simultaneously using a manual lever.