Hi Eric and Franco,
When you connect one soundcard to another the software
has to apply a resampler in order to compensate for
small differences in the sampling speed. That can be
done with small buffers, but I see no way to do it without
buffers.
My motherboard device is HDA Intel PCH ALC887-VD When using
it for input as well as output to Linrad, the delay is 8 ms
at 96kHz sampling in both directions.
With the I option and my RSP1 the delay is about 15 ms which
is similar to what i see with the rtl-sdr dongle.
With the S and T options the delay is around 60 ms, and unstable.
I think that is because of the driver, it can do I/Q balancing
which means it is doing an fft.
There is not really a need for the fft to cause a delay. It is possible
to use the old coefficients for linear combining I and Q and send
the buffer to the PC while storing a copy of the original buffer
and then do the fft for updating the coefficients. It is the long
term average that is needed anyway. The small drawback would be
that the response of the balancing would be a trifle slower
when a strong signal suddenly appears.
The static balancing that Linrad provides is probably good enough,
I do not think it varies much with temperature or frequency.
73
Leif