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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