Real World Digital Audio

• Batch and additional options: Whereas bouncing was once limited

to creating one file at a time, other options are now available in many

DAWs, like bouncing multiple files at once, simple batch processing

tasks, and even automatically burning a track to a CD or adding files to

your iTunes library. These features are unlikely to replace dedicated

tools for batch processing and CD mastering, but they may suffice for

simple chores.

Dithering and Export Quality

Digital systems have to round off sampled values to discrete numbers. The

greater the bit depth, the more values are available to which the samples

can be rounded. (See “Quality in the Digital Domain” in Chapter 1.) But

what happens if you go from a greater bit depth (with more “grid lines” for

dynamic levels) to a lower bit depth (with fewer grid lines)? The digital

audio system will have to round off the numbers to different values, reduc-

ing the dynamic range. As discussed in Chapter 1, that introduces rounding

errors at the bottom end of the dynamic range. These errors are heard as

audible harmonic distortion. In other words, areas of a recording that are

quieter (lower-level dynamics) will sound noisier when the bit depth is

reduced. (See “Digital distortion” in Chapter 7 for examples of employing

this creatively, as with Ableton Live’s Redux effect.)

The easy solution would be to never decrease bit depth, but that’s not

practical. Audio CDs require 16-bit depth, for instance. One alternative is

to always set your project depth at 16-bit, but that doesn’t work well, either.

There are many benefits to adding effects and processing at higher bit

depths even if the final output medium has a lower bit depth. Some 16-bit

projects use 24-bit audio internally (either for internal processing or the

audio interface), as on Pro Tools LE and HD systems, for instance.

You need a way to decrease bit depth without adding distortion. You can’t

eliminate the errors, but you can cover up the audible distortion by using

dithering. Dithering reduces the perceptibility of the distortion introduced

by reducing bit depth by adding random, low-level noise to the downsam-

pled signal. The result is that we perceive less noise during quieter passages

because the errors are randomized rather than being harmonically related to

the signal. The resulting recording sounds better.

Noise shaping is a related technique. Technically it’s not dithering, but shares

the aim of reducing audible noise. Noise shaping shifts the frequency range

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