Digital Sound & Music: Concepts, Applications, & Science, Chapter 5, last updated 6/25/2013
dithering works by adding a small amount of random noise to each sample. You can understand
the advantage of doing this if you consider a situation where a number of consecutive samples
would all round down to 0 (i.e., silence), causing breaks in the sound. If a small random amount
is added to each of these samples, some round up instead of down, smoothing over those breaks.
In general, dithering reduces the perceptibility of the distortion because it causes the distortion to
no longer follow exactly in tandem with the pattern of the true signal. In this situation, low-
amplitude noise is a good trade-off for distortion.
Noise shaping is a method that can be used in conjunction with audio dithering to further
compensate for bit-depth reduction. It works by raising the frequency range of the rounding
error after dithering, putting it into a range where human hearing is less sensitive. When you
reduce the bit depth of an audio file in an audio processing environment, you are often given an
option of applying dithering and noise shaping, as shown in Figure 5.17 Dithering can be done
without noise shaping, but noise shaping is applied only after dithering. Also note that dithering
and noise shaping cannot be done apart from the requantization step because they are embedded
into the way the requantization is done. A popular algorithm for dithering and noise shaping is
the proprietary POW-r (Psychoacoustically Optimized Wordlength Reduction), which is built
into Pro Tools, Logic Pro, Sonar, and Ableton Live.
Dithering and noise shaping are discussed in more detail in Section 5.3.7.
Figure 5.17 Changing bit depth with dither in Logic
5.1.3 Audio Data Streams and Transmission Protocols
Audio data passed from one device to another is referred to as a stream. There are several
different formats for transmitting a digital audio stream between devices. In some cases, you
might want to interconnect two pieces of equipment digitally, but they don’t offer a compatible
transmission protocol. The best thing to do is make sure you purchase equipment that is