[Stk] Fwd: Re: peaks in sin wave

[steffi at hoxel.org]

Thank you for the quick answer.
I tried to start the program under root with nice -18, but the same
peaks occured.
I forgot something to say before, it is only one sample which produces a peak.
I tried different sizes of "bufferFrames" and the distances between
the peaks are exactly of "bufferFrames" size and sometimes multiples.
My soundcard has four channels. When I but the input sin on the first
three and nothing (zero) to the fourth, I get the peaks on the first
three on the same place, but no peak on the fourth channel.
I catched all errors and warning Stk gets/produces about buffers and
the input stream and exit the program if one of those accures. But the
program produces the peaks and is still running.

Stefanie Schmidt

Quoting Stephen Sinclair <sinclair at music.mcgill.ca>:

> Stefanie,
>
> Once in a while an operating system will interrupt processes because
> things like disk activity need to take place, or a number of other
> things.  Linux is not a "hard real-time" system, so these interrupts
> can be expected.  One solution is to try running your app with
> "real-time" priority.  You can set the priority to SCHED_FIFO and
> hopefully the timing behaviour will be more deterministic.  You need
> to run as 'sudo' to get this priority.
>
> Anyways, it's worth a try.  Check the "What to do" section of this
> article for info on how to set thread priority:
>
> http://www.linuxdevices.com/articles/AT5997007602.html
>
> Another thing you might try is using JACK instead, and running JACK at
> real-time priority.  (Which is as simple as an option in QJackCtl)
>
> Steve
>
>
> On Tue, Jan 20, 2009 at 10:47 AM,  <steffi at hoxel.org> wrote:
>> Hallo,
>>
>> I have the following problem.
>> I record a 50Hz sin wave from an USB soundcard with RtWvIn in a wav
>> file. Sometimes I get small peaks in the file, which come not from my
>> input wave.
>> When the sin has positive gradient the peaks are negative and when the
>> sin has negative gradient the peaks are positive.
>> For some reason the distance between those peaks equals the "period
>> length" or multiple of that. With "period length" I mean the value I
>> give to
>> RtWvIn :: RtWvIn( unsigned int nChannels, StkFloat sampleRate, int
>> device, int          bufferFrames, int nBuffers )
>> in the variable "bufferFrames".
>> Sometimes my program runs three days without those peaks and then they
>> appear for 20 minutes or something.
>> On an eee-pc with debian and ALSA version 1.0.16. this peaks appear
>> quite often, while I have not seen them on my laptop with debian and
>> ALSA version 1.0.12rc1.
>>
>> Do you have any ideas?
>> Thank you, Stefanie Schmidt
>>
>>
>> _______________________________________________
>> Stk mailing list
>> Stk at ccrma.stanford.edu
>> http://ccrma-mail.stanford.edu/mailman/listinfo/stk
>>
>>
>>
>




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