In article ],
isw wrote:
As indicated by iTunes, an increasing proportion of mp3s are being
encoded in "joint" stereo. Does it actually "save storage" and
"improve performance" as it is touted to?
IIRC, it's a "sum and difference" process (L+R, L-R), which results in a
lower bitrate for the same quality as compared to encoding the two
channels individually -- the L+R channel is just as easy/difficult to
encode as either L or R alone, while the L-R channel contains a whole
lot less information *in most cases* and so takes a smaller bitrate to
encode. If well done, there's no reason why there should be a reduction
in quality; no information is lost by that process.
It's perhaps worth noting that LP records used what amounts to a
"joint stereo" encoding. The L+R signal is encoded as a horizontal
motion of the stylus, and an L-R difference signal is encoded as
vertical motion.
There were several reasons for doing this - compatibility with older
and less-expensive monaural playback turntables, improved
trackability, etc.
--
Dave Platt AE6EO
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