I've been playing a bit with the levels seen in WAV files and have a couple
of questions.
Given that we're using signed shorts means possible levels of -32768 to
32767.
#1 What should be the desired range of the received signal? If we're
allowing for 60dB that's a factor of 106, right? And, of course you don't
want to clip the thing so allowing -30000 to 30000 or maybe -20000 to 20000
would be good? That would put the 0dB value at 283 or 188 with 9 or 8 bits
of resolution at that point respectively.
#2 if 1-bit (i.e. value of 1) is 0dB then 60dB would be a vale of 106.0
giving less than 1% of the available range and using less than 7 bits of
the 16-bit range. That seems to jive with setting the audio slider to the
middle and adjust input levels to get 30dB. The values in the WAV file are
< 200.
I have both a SignaLink and a Xonar U7. On both of them if I adjust so
that the Window's level meter to show much of anything than I have to slide
the receive gain down considerably which has been stated to be undesirable.
I did find I could add 20dB attenuation to the line from the rig which I've
done now and that has improved things a bit but the audio slider is still
at the 2nd gradation instead of the middle. WAV files now have a max value
of ~5600. I can, of course, decrease the slider and increase rig levels
again to increase that range, But is that desirable?
#3 What should the Windows's level meter show for a desirable receive
strength?
Perhaps we should consider a check of the audio level in the wav data to
ensure it's within some range?
So if it's too low we can tell a user to increase the audio level and too
high to decrease it?
So some range like 20000 absolute value and anything outside that prompts a
one-time message with a reference link that explains how to adjust things?
Anything over 30,000 tell's them to turn it down.
I'm trying to understand the impact of the interaction between WAV audio
level and the WSJT-X processing in order to minimize quantization effects.
Hopefully we can provide some ability to help users adjust appropriately.
RRR
Mike W9MDB
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