FPGA Central

Hello

I've to write a piece of software which can read frequency of input
signal form sound card.
Right now I know how to read PCM (using ALSA). Next I think I have to
do some kind of FFT on the samples I've read. I think about using
fftw3 library, maybe somene already had an eperience with this kind of
problem? Any other solutions will be appreciatted, I've also read
about soundmodem modules, but couldn't find any good documentation how
to use it)

To read PCM I'm using unsigned 16 bits mode, mono and 8kHz sample
rate,
Signal frequency vary from 1,3kHz to 2.3kHz (+/i 10kHz) with sub-
carrier 1.7kHz.
Lower is used for logical "1", higher for logical "0".

Maybe You can tell me how to use a raw PCM samples and convert them
for example to C's tables with integer values or any other more useful
form.

Thanks form advice.
Ignacy

Ignacy wrote:
> Hello
>
> I've to write a piece of software which can read frequency of input
> signal form sound card.
> Right now I know how to read PCM (using ALSA). Next I think I have to
> do some kind of FFT on the samples I've read. I think about using
> fftw3 library, maybe somene already had an eperience with this kind of
> problem? Any other solutions will be appreciatted, I've also read
> about soundmodem modules, but couldn't find any good documentation how
> to use it)

Google "frequency estimation".

> To read PCM I'm using unsigned 16 bits mode, mono and 8kHz sample
> rate,
> Signal frequency vary from 1,3kHz to 2.3kHz (+/i 10kHz) with sub-
> carrier 1.7kHz.
> Lower is used for logical "1", higher for logical "0".
>
> Maybe You can tell me how to use a raw PCM samples and convert them
> for example to C's tables with integer values or any other more useful
> form.

The raw PCM is already integer The MSB is the sign. You need to be sure
that the numbers are sign-extended (the sign bit propagated all the way
to the left) if there more bits in your integer representation than come
from the ADC.

Jerry
--
Engineering is the art of making what you want from things you can get.
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