Image Processing Reference
A simple three-step process when trying to compress and store or deliver audio as
effectively as possible goes like this:
First reduce the sample rate. This proportionally reduces the size of the bit stream.
Encoding only a mono rather than a stereo signal saves half the capacity.
Reduce the variation in the sound level. Even it out so the volume excursions are
not so radical. Filtering to remove noise or unwanted frequencies helps, too.
Shorten the clip somehow. Trim it. Edit bits out. Resample it a little faster with
pitch correction but somehow reduce the total number of samples.
Continuing with Our Travels
So now we know how images are originated on film and video and are converted into a
digital format. Computer graphics systems will contribute more source material, and we
have also considered audio as part of the source of our compressed output.
We now know enough to start looking at the coding processes. We'll concentrate on
video. Audio is interesting but our main focus is visual systems, and the compression of
audio is a large subject in its own right, worthy of much attention. We will come back to
audio near the end of the topic when we set up some example compression processes.
Chapter 37 deals with getting the best out of the sound track.
For now, let's journey onward into the depths of video-coding technology and exam-
ine some popular codecs.