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.

What it 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.

What it doesn't 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.

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.

Real-world examples

• 1.Auto-Tune software plugins
• 2.Live vocal pitch correction processors
• 3.Digital audio workstation (DAW) pitch correction tools