Channels
‐Most audio from computers is either mono with a single channel or stereo with two channels.
‐Low bit rates generally use mono because it requires fewer bits. The industry is evolving to use multichannel (5.1 and 7.1) audio support as well.
Perceptual audio compression
‐Most modern codecs use perceptual encoding techniques:
Æan internal model of the human auditory system determines the important parts of an audio source and spends the available bits on those parts.
Compression efficiency
Ædefined by how many bits are required to reach a particular quality level.
ÆWhen improving compression efficiency, you can choose to lower the data rate while keeping the quality the same, increase the quality while keeping the data rate the same, or pick a point in between.
ÆTypically, the higher the data rate, the smaller the quality differences.
Authoring video for future compression
‐One key to high‐quality compression is creating content that compresses well.
‐There are a variety of techniques for doing this: You can apply these techniques during preproduction, production, or post‐production.
ÆPreproduction: It’s best to introduce the idea of compression early in a project, so all members of the team can consider the implications.
ÆProduction
