Hi Matt,
Just found your article comparing various FreeDV modes and SSB on AWGN
channels:
http://www.kk5jy.net/snr-freedv/
Very good work. I feel your AGWN buries SSB more than mine done. Never
quite sure how to model SSB myself, my peaks tend to stick above the
noise. Feel I need to model the clipping/ALC on the PA somehow.
Carl, VE3APY, suggested we put a link on freedv.org to your article on
building FreeDV for the RPi:
http://www.kk5jy.net/freedv-build/
So I've placed a link in the documentation section.
Pls feel free to tell us about any further articles you write on this
list or the digitalvoice Google group.
Cheers,
David
On 28/05/18 20:48, Matt Roberts wrote:
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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