Perceptual coding

Introduction:

   Perceptual audio coding is a method of encoding audio that uses psychoacoustic models to discard data said to be unable to be perceived by humans.

Perceptual Coding

Perceptual audio coding is a method of compression for digital sound which eliminates frequencies the human ear cannot hear. It may also eliminate softer sounds that are being drowned out by louder sounds, which is taking advantage of what is known as Masking. Reason to use perceptual audio coding is to reduce file size since high quality audio with no compression can be very big. Perceptual audio coding is a compression known as lossy audio compression because it is “losing” pieces of sounds (the ones removed that we cannot hear). The other type of compression is lossless, which takes repetitive information and encode them to symbols and equations to take up less space. This also allows you to remake an exact copy of the original. Even though lossless compression may seem better since it still keeps all the information, it does not compress as well as lossy compression does.

Now let’s back up for a moment. Sound does not start off as digital, it is analog.

Sampling Example

So to even use perceptual audio coding we need to convert audio into digital. We have to use an audio codec to change analog sound into pulse-code modulation, a digital representation of analog. To get the digital representation as close as possible to the analog, there are a few factors that can be adjusted, and the better these factors are, the bigger the file will be. First factor is sampling rate; this determines how often the waveform is measured. Second factor is sampling resolution which is the measurement of each sample point on a scale, which the scale will have more measure points the higher the resolution is. Then by using the method known as quantization, the number is rounded to the nearest whole number.

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