Tim Gimmel wrote:
> The new portaudio stuff in Fldigi 2.05 fixed my problem with the
> "ticking" sound. Can you tell me how it (portaudio) works, or give me
> some hints that I can give to the alsa folks? WSJT 6 uses portaudio
> also and would love to be able to make it work correctly. I have to
> admit I have been working with Linux for over 10 years and I still just
> don't understand the audio system. If you know of a site that has a
> good explanation of Linux audio from oss to alsa to portaudio I would
> love to read it!
Portaudio is a cross platform API. It sits between your application and
the underlying sound system, in most cases folks are using ALSA.
In your case, you were able to use Portaudio and the FLdigi code to
force a supported sample rate that your Intel HD sound card could handle
natively. This is 44,100, 48,000. The card won't support lower sample
rates, but digital apps want to use them, like 8000, 11,025, etc. There
are a variety of standard sample rates for sound cards, yours does not
support all of these (at least in Linux and ALSA.) And that's why the
ticking. ALSA had to up convert, and the Intel HD driver for ALSA is not
up to the task right now.
Portaudio and a forced (in FLDIGI) supported sample rate fixed the
ticking because no conversion was then needed on the sound stream.
If WSJT can select a sample rate, you should be able to take care of the
problem easily. You might want to ask Joe to put that in the code.
Rick Kunath, k9ao