Digital Sound & Music: Concepts, Applications, & Science, Chapter 5, last updated 6/25/2013
52
noise from dither only
noise from dither with
noise shaping
Figure 5.42 Closeup of noise from dither and noise from dither with noise shaping (quantization
noise included)
You can see this also in the spectral view of the noise files in Figure 5.43. In a spectral
view of an audio file, time is on the x-axis, frequency is on the y-axis, and the amplitude of the
frequency is represented by the color at each (x,y) point. The lowest amplitude is represented by
blue, medium amplitudes move from red to orange, and the highest amplitudes move from
yellow to white. You can see that when dithering alone is applied, the noise is spread out over
all frequencies. When noise shaping is added to dithering, there is less noise at low frequency
and more noise at high frequency. The effect is to pull more of the noise to high frequencies,
where it is noticed less by human ears. (ADCs also can filter out the high frequency noise if it is
above the Nyquist frequency.)
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