On 17/09/16 18:28, glen english wrote:
> Yeah.
> Cascading codecs is always trouble.
> BTW My understand of the word TRANSCODING is going between one encoded 
> method and another without going back all the way to uncompressed. Going 
> between different video encoding methods usually done by transcoding. 
> Most video encoding is all DCT / macroblock based so is probably more 
> relationship between codecs than speech codec variations....
> In this problematic voip case:  uncoded PCM (microphone)  >> AMBE2 >> 
> over air >> decoded >> PCM >> uLaw encode>> ulaw decode >> headset. (and 
> reverse) .

Transcoding is going from one format to another, and when the
destination is a lossy format, that will mean a reduction in quality.

Decoding to uncompressed shouldn't incur loss compared with a
hypothetical conversion from AMBE2 direct to µ-law, more likely the
assumptions made by the µ-law CODEC don't hold true for the synthesized
voice from the AMBE2 CODEC, and that would be why it sounds so terrible.

Stuart Longland (aka Redhatter, VK4MSL)

I haven't lost my mind...
  ...it's backed up on a tape somewhere.

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