[hpsdr] best audio sample size?

[John Laur]

John,

I would suggest simply that 48000Hz, 16bit is best practice unless you are
very sure of the reason you need something else.

At the end of the DSP chain the internal audio is 48000Hz, 32bit float, so
24bit or 32bit audio on VAC is possible given driver support, but 16bit is
most compatible and provides 96dB of dynamic range which I have never found
to be insufficient for digital modes so long as your have adjusted your
gain appropriately for the mode in question. Adjusting the audio samplerate
higher will simply cause it to be upsampled inside of PowerSDR and is not
useful unless you are sending IQ data over VAC instead of audio.

Make sure all of the windows shared samplerates under the playback and
recording device properties are set to 48000hz/16bit as well to prevent
inadvertent resampling artifacts if the audio device happens to be opened
in shared mode.

73, John K5IT

On Mon, Apr 6, 2015 at 1:07 PM, john clark <n0ure at yahoo.com> wrote:

> ***** High Performance Software Defined Radio Discussion List *****
>
>
> I know that we are all hopeful that in the future all of our digital modes
> will be directly decoded and the need for VAC and all the other sources of
> conversion errors will be bypassed, but until then I am trying to set my
> audio chains to the optimum values. I read that WSjt-x and HRD DM-780
> prefer the audio samples delivered 48000 samples per second, my question is
> At what bit size?. 16, 24, 32?  What can PowerSDR VAC1 accept/deliver?
>
> From WSJT-x I read
>
> "Receiving
> *WSJT-X* acquires 16-bit integer samples from the audio input device at a
> 48000 Hz rate and immediately downsamples the stream to 12000 Hz. Spectra
> from overlapping segments are computed for the waterfall display and saved
> at intervals of 0.188 s, half the JT9 symbol length."
>
>
> When I set the VAC channel to 24 bits per sample WSjt-x complains. If I
> open up VAC I can see that wsjt-x pushes VAC  to 16 pits per sample on the
> input but I also see 24 pits per sample on the output VAC channel.
>
> What can PowerSDR work with? How can I set the pits per sample on the
> audio channels?
>
> John
>
> Ti4/N0URE
>
>
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