Hi David,
The tests I have been doing are also all in software. I'm working on a
short article for my website, comparing the various Codec2 modems to
analog voice at various SNRs.
To do this, I cooked a script that takes a voice recording, encodes it,
then adds AGWN to the digital version before decoding it. At the same
time, they add the same level of AGWN to the original file for
comparison. The scripts also use 'gnuplot' to make a visual thumbnail
of each waveform.
The result is both an audio and visual comparison of each modem to an
analog signal with the same SNR. Since it's all scripted, I can
generate lots of different samples, but without introducing any random
human error.
You are correct, AGWN is a poor estimate for certain kinds of HF
distortion. That said, even in AGWN, the results are very educational,
especially being able to *hear* the difference between analog and
digital at a given SNR.
73,
Matt
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