Under what ham situations is PulseAudio useful? I understand it's
useful for shared audio desktop stuff, but I don't understand what it
does for radio DSP. A quick read of
http://en.wikipedia.org/wiki/PulseAudio firms up my confusion.
Portaudio is an API, albeit portable, just as OSS is now (mostly) an API
to ALSA (non-portable).
Something that might clarify understanding for fldigi users: the USB
audio interface is a "class standard." They can all use the same
"driver," and do on Linux, although a few devices have what are called
"quirks," which are either workarounds for bugs or are special settings.
An example of a quirk is the EMU-0202; I recently helped implement the
48KHz and 96KHz sampling rate features, and it's done as a special case
for the device in the USB sound driver, but the code size is very small,
a half dozen line at most, and it's all just setting control values.
Dave's point about sample rate conversion is a set of "favors" being
done for users by the API or mid-tier software, not the USB Audio driver
itself, which is essentially the same across all USB cards regardless of
what chipset is used or how much it cost. Choosing OSS or PortAudio
lets you decide which mid-tier software is doing you which favors. Most
of the favors there are done for music recording, and the performance
and operations decisions aren't necessarily optimal for ham use.
Leigh/WA5ZNU
On 02/13/2010 11:20 AM, w1hkj wrote:
Peter Hamilton wrote:
The reason for the difference is....
Interesting. Linux audio does seem to be a can of worms. The one
consistent trend I've noticed is that the more "primitive" the sound
subsystem the better it is in this application. Less versatile, maybe. I
had no end of problems with Pulseaudio, Portaudio had a few minor
problems but was basically OK apart from this, and OSS seems rock solid.
Really a function of the drivers that have been written for the h/w.
OSS has the least amount of support in the newest distributions. It
will also be the most likely to give resampling errors. Portaudio
resampling is done internally in fldigi using high quality sample rate
converters. Pulseaudio allows the user to select the sample rate
converter (some choices are the same as fldigi's converters).
If you notice tx audio clicks or dropouts then abandon the OSS audio
i/o. The culprit will be a grossly inadequate sample rate converter
in the OSS driver.
Dave, W1HKJ
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