{
  "patent_number": "US 5973252",
  "country": "US",
  "title": "How Real-Time Pitch Correction and Auto-Tune Technology Works",
  "original_title": "Pitch detection and intonation correction apparatus and method",
  "summary": "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_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."
  ],
  "filed": "1998-10-15",
  "granted": "1999-10-26",
  "expires": "2018-10-15",
  "status": "expired",
  "holder": "Auburn Audio Technologies Inc",
  "holder_url": "https://patentbrief.org/company/auburn-audio-technologies-inc",
  "inventors": [
    {
      "name": "Harold A. Hildebrand",
      "url": "https://patentbrief.org/inventor/harold-a-hildebrand"
    }
  ],
  "times_cited": 39,
  "tags": [
    "consumer_electronics",
    "software"
  ],
  "abstract": "A device and method is disclosed to correct intonation errors and generate vibrato in solo instruments and vocal performances in real time. The device determines the pitch of a musical note produced by voice or instrument and shifts the pitch of that note to produce a very high quality, high fidelity output. The device includes a pitch detector that automatically recognizes the pitch of musical notes quickly. The detected pitch is then used as an input to a pitch corrector that converts the pitch of the input to an output with a desired pitch. The corrected musical note is then in tune with the pitch standard. The device and method employ a microprocessor that samples the signal from a musical instrument or voice at regular intervals using an analog-to-digital converter and then utilizes data derived from an auto-correlation function of the waveform to continuously determine the period of the waveform. The period of the waveform is then compared to a desired period or periods (such as found in a scale). The ratio of the waveform period and the desired period is computed to re-sample the waveform. This ratio is smoothed over time to remove instantaneous output pitch changes. The ratio is used to resample the input waveform. The resulting output waveform is processed through a digital-to-analog converter and output through audio interfaces.",
  "url": "https://patentbrief.org/patent/us/5973252/auto-tune-pitch-correction",
  "markdown_url": "https://patentbrief.org/patent/us/5973252/auto-tune-pitch-correction/md",
  "google_patents_url": "https://patents.google.com/patent/US5973252",
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}