Image Processing Reference
or HE-AAC concept was developed by a company called Coding
Technologies. Note that the nomenclature AAC
, AAC Plus, and MPEG-4 HE-AAC are all
describing the same thing. The codec is becoming best known as HE-AAC.
Here is a rundown of some common multi-channel formats. There are many more, and you
must consult any records that may be attached to the source material and read the manu-
als for your encoding software to know how to map these to the output encoded media.
Table 7-2 Audio Track Arrangements
Old legacy program material will only have a single
audio track. You must duplicate this across both
tracks of a stereo pair for most applications. It is
very likely that home movie audio from magnetic
striped film will only have mono audio.
This is the duplicated mono on two stereo channels.
The radio news-gathering format uses 2-track tapes
but records one track in each direction, requiring
that the tape be turned over to record the other
True stereo recorded through a pair of microphones
or mixed from multi-channel master tapes. Be
careful to preserve the relative phasing between
channels or sound will appear to move around.
Sometimes old mono recordings will be reprocessed
with filters to separate out various instruments that
are then panned from one side to the other to create
an artificial stereo effect.
Sometimes, the stereo signals are not a stereo pair in
the true sense. One could be a backing track while
the other is the same but with perhaps the vocals
missing. In news gathering, one channel is probably
ambient background noise while the other is the
presenter. The two channels must be mixed carefully
to turn them into a presentable stereo sound track.
Coding Technologies: http://www.codingtechnologies.com/