[speex-dev] Way to measure loss of quality

[Thomas S]

2 things, first an idea... next a question.

QUALITY MEASUREMENT IDEA:
I find it difficult to hear 2 voice samples and tell
which is nearer the original, especially if the
background hiss is slightly different. So what if you
actually subtract the post-compression sound from the
original and then listen to the DIFFERENCE. If you
can't hear any voice except background noise and some
hiss from "s"'s and "d"'s and such, that means most of
the actual voice has been maintained. If you can hear
someone speaking, that means there is leftover voice.
If you can actually understand what that someone is
saying, the difference is great. Thoughts?

QUESTIONS:
My hearing is not the best I suppose, because I can
barely tell the difference between any of the
encodings and the original for the examples hosted on
the Speex.org website. When I encode, I can barely
tell the difference between quality 3 and quality 10.
Complexity is at 8 or above. SO my questions are:

1. What would be a common quality level for 56k modems
to use in voice chat during a game? CPU usage is not
an issue.
2. Would it be better to have 16khz at quality
3(complex10) or 8khz at quality 5, they end up roughly
the same size? (let me know if you are refering to VBR
or not or both)

Thanks to those who have enough experience to have a
general idea of this illusive "quality" stuff I'm
asking about.

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