Hi Pete,
the quality of the re-sampling varies considerably with the operating
system version, Windows XP for example had very poor performance and
degraded the audio quality considerably if forced to do a non-integrally
related re-sampling, in fact I believe even integrally related
re-sampling was poor. Vista improved matters but still had problems
which WSJT-X explicitly works around. From Windows 7 onwards things are
much better but choosing the optimal sound card default sample rate is
always the best option.
If you plan to continue using WSJT *and* WSJT-X then a separate sound
card might be best but personally I would use WSJT-X and work with the
developers to isolate and improve any facilities where WSJT has a
perceived and measurable advantage over WSJT-X.
73
Bill
G4WJS.
On 01/01/2018 11:38, Peter Connors wrote:
Hi Bill
Aha! Resampling, so that's what's happening. I hadn't realised that
the OS would do that by itself. I see no evidence in practice of
sub-optimal results because of this but perhaps the effects are more
subtle than my operation will show.
I will try a 44100 rate and see what WSJT-X makes of that. Or maybe
sound card no4 is called for...
73, Pete G4PLZ
On 01/01/2018 11:22, Bill Somerville wrote:
On 01/01/2018 10:10, Peter Connors wrote:
I first installed WSJT (first 10 then 9.7) I read the user manual
and got ready to calibrate the audio feed.
I started with the same 48kHz 16-bit input I had been using for
WSJT-X and was intrigued to notice that, with the Rate in and Rate
out still set at 1, the 'lower left' numbers varied between only
1.0001 and 0.9999. At the next moonrise it was decoding and
displaying well and remains so.
Have I entered a chronosynclastic infundibulum?
Pete G4PLZ
Hi Pete,
WSJT requests 44100 Hz audio streams whereas WSJT-X requests 48000 Hz
audio streams. Both will work with the sound card default sample rate
set to either but not having the default set at the same as the
application's requested rate will cause the operating system to
re-sample the streams to achieve he desired rates. Such re-sampling
is not optimal as the two rates are not related by an integral
factor. If you mainly use WSJT I recommend setting the sound card
default rate to 44100 Hz 16-bit and if you mainly use WSJT-X set the
sound card default sample rate to 48000 16-bit. Setting a higher
rates that are related by integral factors with the desired rate
(e.g. 96000 Hz or 192000 Hz when a 48000 Hz stream is required) will
not degrade the audio quality but it gains nothing either. Similarly
selecting 24-bit samples loses nothing but gains nothing either as
the lower 8-bits of each sample will be discarded when a 16-bit
stream is requested.
Small random variations in the measured sample rate are probably due
to varying software latencies rather than sound card sample clock
jitter or error and can be ignored, OTOH consistently greater than or
less than unity indicates a clock accuracy issue that you can correct
for in WSJT.
73
Bill
G4WJS.
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