2008/2/19, Clemens Ladisch clemens@ladisch.de:

Ignacy Kasperowicz wrote:

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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.

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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 ;)