Bill,
typical SDR console applications deliver samples via audio devices, some
have other mechanisms but most of those are not to a common standard.
What is actually passed over an audio device stream need not be audio,
for example many (most) SDR consoles are capable of producing (and
consuming in a few transceiver cases) I/Q sample data as a stereo pair
of interleaved I and Q data streams. This is usually necessary since
consuming applications wish to constrain the sample rate and do not want
the full bandwidth of the SDR sampling circuits - this is what the SDR
console application should be doing to provide the sample rate the
consumer requests. Nor do consuming applications wish to control the
ever increasing number of SDRs, e.g. to set the centre frequency, filter
settings, gain settings, etc., each with their own proprietary mechanism.
WSJT-X is not a general purpose SDR console, currently it consumes a
baseband 16-bit PCM audio sample stream at 48,000 Hz sample rate. In
future it may have a wide-band option to consume something along the
lines of a 96,000 Hz I/Q data stream pair. Note this is a non-trivial
change as the DSP processing in WSJT-X is built on the assumption that
the input data is 48,000 Hz bandwidth, and furthermore the first
processing step is a downsample and LPF to 12,000 Hz. It is not really
relevant that the data arrives a baseband PCM audio, rather it is the
bandwidth requirement that determines the following processing steps to
decode signals.
So to answer your question, no to the first, WSJT-X is not trying to be
a general purpose SDR console. As to the second, it is not really
relevant how the sample stream is delivered, but as PCM data, perhaps
misused repurposed to covey I/Q data, it is a very convenient
cross-platform data transfer mechanism for sample data. Note there
should be no "Windows audio processing" if the sample rate is consistent
throughout and the levels are set to 0 dB (FS) throughout.
73
Bill
G4WJS.
On 01/11/2021 13:59, Bill Barrett via wsjt-devel wrote:
Hello Bill-
Do you see a possibility that WSJT-X might one day have a direct
connection to SDR Digital Data Stream input bypassing the typical DAX
module and Windows audio processing?
Thanks;
Bill W2PKY
On Mon, Nov 1, 2021 at 9:48 AM Bill Somerville via wsjt-devel
<wsjt-devel@lists.sourceforge.net> wrote:
On 01/11/2021 12:22, Dave Fitches via wsjt-devel wrote:
> I recently got another RTL-SDR to hook up to my system. (Win 10)
>
> I was planning to run one using WSJT-X running FT8, the other
another
> running WSPR
>
> However... it seems that WSJT-X will only recognise ONE Virtual
Audio
> Cable (VAC)...
>
> I recently set up two additional VAC's (for a total of three)
and they
> work perfectly - unless I'm using WSXT-X which will only
recognise ONE
> on the Soundcard Input feed, though it DOES show all THREE VAC's on
> the OUTBOUND sound card selection...
>
> Similarly (and no surprise because it's using the same code)
JS8Call
> has the same issues.
>
> I'm using the VAC software from V.Burel / JS-Loezic -
> https://vb-audio.com/Cable/
>
> --
>
>
> = Dave Fitches =
Hi Dave,
no one else has reported a similar issue. I have VAC installed (not
VB-Cable but similar) with 8 devices and that all show up in both
WSJT-X
audio input and out devices as expected. do other applications
that use
audio devices via the MME audio sub-subsystem like Audacity show them?
73
Bill
G4WJS.
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