Tony Mountifield wrote:
In article <[EMAIL PROTECTED]>,
Andrew Kohlsmith <[EMAIL PROTECTED]> wrote:
You can convert between ulaw and alaw 10000 times and it'll sound exactly the
same as the original 8000Hz 16-bit sample because... well... it is.
Just to pick a nit, the above can't be right. G.711 is a logarithmic
recoding of 16 bits into 8. So each 8-bit value can be reached from
a whole lot of different 16-bit values. The information as to which
16-bit value it came from is lost, so you can't get back to the
original values, just to approximations of them.
Also, I believe the 16-bit range is chopped up in slightly different
places for aLaw than for uLaw, which could mean a slight loss of
information going back and forth repeatedly between the two.
Cheers
Tony
It is actually 12 or 13 bits compressed to 8. As you say, it is lossy.
However, after the first round trip, subsequent round trips give the
same answer. This was a design requirement. Tandem operation was not
allowed to give endless degradation. Even G.726 follows this rule. You
can chain a mixture of G.711 and G.726 links, without the degradation
building up. It is one of the reasons G.726 is so very complex for an
ADPCM codec.
Regards,
Steve
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