Frank Carmickle frankiec at
Tue Nov 6 04:57:25 EST 2001

Hi Deedra

What synth are you using?  I'm gonna guess it's a dec express?  Yes you
guys are some what on to this as a kernel audio driver problem.  It
probably will go away with 0.5.11 alsa but it's probably going to reappear
when you move to 0.9 alsa.  That is unless you make the buffer sizes large
enough.  It is generally the case with mp3 players to have a large buffer
size.  You may notice that you will need to pass aplay the flags to open
the audio hardware with a larger buffer size.

What's happening here is that speakup needs to use the processor to send
it's data to the serial port for your synth.  If your reading your
probably sending 50ms worth of stuff sleeping for 500ms and waking up
again to do the process all over.  When you only have a few ms worth of
audio buffered this is gonna run out quickly.  

Most of the time no body really cares if there audio takes 100 ms longer
to start and stop playing so it isn't a problem.  Most of us really enjoy
having a kernel based screen review package so what do you do.  If you
really need lowish latency your going to either have to get a machine with
more then 1 cpu or get a second machine to use as a terminal just to run
speakup on.  But like I said most folks will never need this.  Only those
of us who want to use a low latency audio recording and editing
environment will need this.  

The linux audio development folks have been working hard on pushing the
alsa and kernel folks to make linux a viable low latency operating system
for audio.  There doing a good job with it.  Right now it is required to
patch the kernel with Andrew Morton's lowish latency patches.  There is
also a preemptive patch that gets similar results which uses a totally
different principle to achieve the results.  Uncle Linus doesn't really
like any of the offered solutions thus far.  Let's hope that they get this
stuff hammered out during the 2.5 tree so we can have alsa and low
latency kernels when 2.6 is released.

To whom ever it was that wrote about timings your sort of missing the
point.  You can sit there and stare at the rtc til the cows come home.  
But if they took your cpu away from you for 50ms what are you going to do?

     Frank Carmickle
phone:     412 761-9568
email:     frankiec at

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