[alsa-devel] Problem with setting period time and buffer time.

[Ignacy Kasperowicz]

2008/2/19, Clemens Ladisch <clemens at ladisch.de>:
> Ignacy Kasperowicz wrote:
> >> Just write the data to the device.
> >
> > Ok, but when I just write data to the device I don't really know how
> > long it'll be playing.
>
> But you know how many sample you are writing, and you know the sample
> rate.
>
> > There is no problem when I've infinite loop with writei inside. but I
> > need to change freq of my sound signal with exact 843 us period time.
>
> Assuming a sample rate of 48 kHz, 1/1200 s corresponds to exactly
> 40 samples.  At 44.1 kHz, this would be 36.75 samples, so you'd have to
> use groups of 37+37+37+36 samples with appropriate phase shifting.
>
> BTW: 1 / 1200 Hz = 833.33... µs
>
>
> HTH
> Clemens
>

Thanks for correction, I was trying to make this too complicated :P
I dunno why I even thought about just setting how many samples to
write in writei() :P

Although, when from calculations indeed I should set 40 samples to get
sine played for 1/1200Hz, in my code I need to set frames size value
for 400. Do You know why? I have 48kHz rate, one channel and 16 bit
PCM.
From what I've read there:
https://bugtrack.alsa-project.org/wiki/wikka.php?wakka=FramesPeriods ,
"A frame is equivalent of one sample being played" so why I need
multiply calculation result by 10 ?
I think this is a last rookie question :)

Thanks for answers :)
ignacy

PS. Yeah I know its 833.33...us, I've just rounded it up for experimenting ;)


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