Ben Bradley wrote:

I think this utter crap goes under the fancy name of
Linear Predictive Coding

Which ecompasses RELP, CELP, VSELP and other variants.



does SERIOUS compression of a phone audio signal.
To call the sound robotic is an insult to talking robots
worldwide. Whenever I hear it I start lusting for a +/-6dB
300-3.5k response analog line.

Absolutely true for the 2.4 kbps Inmarsat stuff we were using around 1990. Pretty true for the vast majority of 10kbps stuff we've been living with over the past decade. Marginally true for the 12kbps stuff we've seen over the past 5 years or so. Not true at all for the newest high bandwidth stuff which will probably become the next generation's "toll quality" benchmark.