не знаю как описать, поэтому вот:
*Dithering:
Dithering is the practice of adding noise to a signal to mask quantization noise.

*Quantization Noise:
Quantization noise is a result of describing an analog signal in discrete digital terms (see quantization). This noise is most easily heard in low-resolution digital sounds that have low bit depths and sounds like a shhhhh-type sound while the audio is playing. It becomes more apparent when the signal is at low levels, such as during a fade out.