[linux-audio-user] emu10k1 multichannel support

[Lee Revell]

On Sat, 2005-01-22 at 08:17 +1100, Shayne O'Connor wrote:
> oops - that is what i meant to write :)
> 
> but i probly should've been more clear - i tried my usual start-up
> command on hw:0 (with the 44100 rate) in *addition* to trying it at
> 48000 ... same result (avalanche of x-runs).
> 
> i meant to say that i tried (pretty much) all settings (different sample
> rates, buffer periods, memory lock/no memory lock) but nothing would get
> rid of them x-runs on hw:0 - not even a sample-rate of 48000.
> 

OK.  I cannot reproduce your problem.  It works fine for me at all of
the above settings, even 44100.  I will revert the PCM handling to the
old method and see if this works for you.

> 
> i've heard a lot of negative stuff about creative's native (?) 48000Hz
> sampling rate - not being too technically adept, i'm wondering what is
> really going on ... is *everything* put in through the ac97 codec
> (that's the input port, no?) sampled at that rate? what does this mean
> if i'm always setting jack (without the patched alsa) to record at
> 44100Hz? i know that things start sounding funny if you record at 48000
> and then playback/downsample to a different rate .....
> 

The DSP runs at 48000 natively, and does hardware sample rate conversion
for all other rates.  The exception is multichannel recording, which
only works at 16bit, 48000Hz, because you are directly capturing the
outputs of the internal DSP before it goes through any rate conversion.
Also, there is only one stereo sample rate converter for capture, while
for playback each of the 64 voices has its own SRC.

These hardware SRCs are good quality, because emu10k1 is really a
hardware synthesizer that also can do PCM, the exact same hardware is
used for pitch shifting by the synth as sample rate conversion for PCM.
In practice there are some bugs but these can be worked around in the
driver.

> should i *always* be using 48000Hz when recording on an emu10k1 card? if
> so, what's the best way to get a finished project down to CD-style
> 44100Hz without making it sound wierd?
> 

The best way to use this card is to run at 48000HZ and then when you are
done resample to 44100 using a high quality software resampler.  OTOH,
if you are working with a bunch of 44100Hz samples, you can run JACK at
44100Hz, if it sounds good to you.  Multichannel playback at 44100
should be supported eventually.  Although, keep in mind the kX driver
doesn't support this yet, and they have docs from Creative.  But you
won't get the multichannel recording functionality at this samplerate.

If you are using it for live recording or effects processing then you
should certainly run at 48000.

Lee