Compression - week 11

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  • Compression
    • Lossy
      • Constant size, Variable quality
      • Uses psycho-acoustic audio masking removing inaudible data
        • Temporal masking
          • Removing faint sounds that can't be heard for a short time after loud sounds
        • Range thresholds
          • Using the Fletcher-Munson to band limit the audio signal based on the range of human hearing
        • Simultaneous masking
          • One sound masks out another sound, by level or frequency, played at the same time
        • Frames the data and analyses frequency bands for each frame
      • Can't be decompressed back to it's original state
      • Not ideal for archive data storage
      • Can Compress to 1/10 of original size
    • Lossless
      • Compresses less than Lossy
      • Preserves information and can be decompressed
      • Reduces redundancy
        • Pattern recognition
          • RLE (Run Length Encoding)  - finding repetitions in audio samples
            • Encoding continuous runs of data into an multiplier and a sample of the dataword


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