{
  "patent_number": "US 5579430",
  "country": "US",
  "title": "How Digital Audio Compression Works",
  "original_title": "Digital encoding process",
  "summary": "A foundational method for compressing digital audio by transforming sound into spectral data and using variable-length codes to store it efficiently.",
  "what_it_does": "This patent describes a process to shrink digital audio files by converting sound waves into spectral data using a filter bank. It then quantizes this data, meaning it reduces the precision of less audible sounds while keeping important ones intact. The core mechanism uses an 'optimum encoder' that assigns shorter binary codes to frequently occurring data points and longer codes to rare ones, similar to how Morse code uses shorter signals for common letters. It also uses a clever 'escape' mechanism where values outside a common range are assigned a special identifier, which keeps the lookup tables small and manageable.",
  "what_it_does_not_cover": [
    "Does not cover raw, uncompressed audio formats like WAV or AIFF.",
    "Does not cover non-spectral compression techniques like simple pulse-code modulation (PCM) without the described entropy coding.",
    "Does not cover hardware-specific playback circuitry or digital-to-analog converters.",
    "Does not cover loss-less audio compression methods that do not use spectral transformation and quantization."
  ],
  "filed": "1995-01-26",
  "granted": "1996-11-26",
  "expires": "2015-01-26",
  "status": "expired",
  "holder": "Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV",
  "holder_url": "https://patentbrief.org/company/fraunhofer-gesellschaft-zur-foerderung-der-angewandten-forschung-ev",
  "inventors": [
    {
      "name": "Bernhard Grill",
      "url": "https://patentbrief.org/inventor/bernhard-grill"
    },
    {
      "name": "Karl-Heinz Brandenburg",
      "url": "https://patentbrief.org/inventor/karl-heinz-brandenburg"
    },
    {
      "name": "Thomas Sporer",
      "url": "https://patentbrief.org/inventor/thomas-sporer"
    },
    {
      "name": "Bernd Kurten",
      "url": "https://patentbrief.org/inventor/bernd-kurten"
    },
    {
      "name": "Ernst Eberlein",
      "url": "https://patentbrief.org/inventor/ernst-eberlein"
    }
  ],
  "times_cited": 108,
  "tags": [
    "consumer_electronics",
    "telecommunications",
    "software"
  ],
  "abstract": "A digital encoding process for transmitting and/or storing acoustical signals and, in particular, music signals, in which scanned values of the acoustical signal are transformed by means of a transformation or a filter bank into a sequence of second scanned values, which reproduce the spectral composition of the acoustical signal, and the sequence of second scanned values is quantized in accordance with the requirements with varying precision and is partially or entirely encoded by an optimum encoder, and in which a corresponding decoding and inverse transformation takes place during the reproduction. An encoder is utilized in a manner in which the occurrence probability of the quantized spectral coefficient is correlated to the length of the code in such a way that the more frequently the spectral coefficient occurs, the shorter the code word. A code word and, if needed, a supplementary code is allocated to several elements of the sequence or to a value range in order to reduce the size of the table of the encoder. A portion of the code words of variable length are arranged in a raster, and the remaining code words are distributed in the gaps still left so that the beginning of a code word can be more easily found without completely decoding or in the event of faulty transmission.",
  "url": "https://patentbrief.org/patent/us/5579430/digital-encoding-process",
  "markdown_url": "https://patentbrief.org/patent/us/5579430/digital-encoding-process/md",
  "google_patents_url": "https://patents.google.com/patent/US5579430",
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}