# 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. - [Smart Speaker System Adapts Sound Based on Speaker Placement](https://patentbrief.org/patent/us/11743673/audio-processing-apparatus-and-method-therefor) — This patent describes an audio system that intelligently chooses how to play different parts of a sound through different speakers, adapting its method based on where each speaker is placed in a room. - [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 Smart Speakers Adapt Sound to Your Room and Listening Spot](https://patentbrief.org/patent/us/11178503/system-for-rendering-and-playback-of-object-based-audio-in-various-listening-env) — This patent describes a system that automatically adjusts how spatial audio sounds in a room by sensing speaker locations, listener position, and room acoustics, then dynamically calibrating the sound output. - [How Voice Assistants Change Their Speech Based on How You Talk](https://patentbrief.org/patent/us/10276149/dynamic-text-to-speech-output) — This patent describes a system where a voice-controlled device adjusts its text-to-speech output characteristics, like speed or tone, based on the user's speaking habits or current situation, making responses feel more natural and personalized.