[linux-audio-user] sounblaster live platinum and full-duplex recording (noisy)

Erik Steffl steffl at bigfoot.com
Mon Aug 16 02:09:46 EDT 2004


Lee Revell wrote:
> On Fri, 2004-08-13 at 23:30, Erik Steffl wrote:
> 
>>   recording seems to be working OK but:
>>
>>   in audacity when I record the track it sounds OK
>>
>>   however if I generate click track and record then (the click track is 
>>playing while I am recording) the recording is really bad (noisy, low 
>>quality).
>>
>>   I vaguely remember something about full-duplex on sounblaster not 
>>being very good, i.e. there's something wrong when using it but don't 
>>remember what (bitrate being forced to be very low or something along 
>>those lines).
>>
>>   However I can't find any information on that subject now (I tried 
>>google and creative site), does anybody know details and/or have some 
>>pointers to relevant docs?
>>
>>   system: debian unstable, 2.6.5 kenrel (with alsa), sounblaster live 
>>platinum (with live drive).
>>
> 
> 
> The hw:x,0 capture device on the sb live is not very good.  For good
> results you have to use the hw:x,0 playback device and the hw:x,2
> capture device.  You have to use 48khz.
> 
> To record at the lowest latencies you have to record more than 2
> channels.  This is because the capture buffer size is fixed in bytes;
> doubling the number of channels halves the amount of time between
> interrupts with a fixed buffer size.
> 
> This did not work at all until very recently, I believe you need the
> ALSA 1.0.6-rc1 release candidate.
> 
> Search the recent alsa-devel archives for 'emu10k1 low latency capture'
> and 'emu10k1 multichannel' for more info.

   thanks for the info, now I have to figure out how to use it:-) it 
looks like audacity uses oss (/dev/dsp) so I guess I could configure 
alsa so that /dev/dsp is hw:x,0 and e.g. /dev/dsp1 is hw:x,2

   right now I'm not even at the point of caring for latency, for some 
reason the recording is of really bad quality when I use full-duplex 
(i.e. playback of click track and record), the quality is OK if I only 
record.

	erik



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