On Mon, Nov 29, 2010 at 3:54 PM, Bill Unruh <[email protected]> wrote:
> On Mon, 29 Nov 2010, Sathishkumar Duraisamy wrote:
>
> Dear all,
>>
>> I am new to the list and to the alsa library. In my application, I have to
>> collect data from outside world in the form of voltage, and then plot. I
>> have done the plotting and GUI parts of the application. Now I have to use
>> an ADC to collect the data.
>>
>> My question: Is it possible to use the ADC of audio input and alsa lib to
>> get the sample from the outside world. Have anyone tried like this. If it
>> so
>> can you please guide me how I can get started?
>>
>
> Sure. Just use the source code for arecord as a sample. But there are some
> limitations. Almost all audio cards do not go down to DC
> intpu level but have a low frequency cutoff of about 10Hz. Thus if your
> project requires low frequency levels, you are out of luck. Also most sound
> cards have a pretty hard cutoff about about 20KHz since this
> is the highest sound humans can hear and corresponds to the upper
> frequencymeasurable by a 44.1 frequncy card. If you allow in higher
> frequencies you get distortion int hat the high frequencies are floded over
> into the low frequency band. The tird problem is normaisation-- ie you
> really
> have to put in a test signal of a known voltage to calibrate your card's
> amplitude -voltage characteristic.
>
>
Thanks Unruh. superb explanation. Now I started to analyse things with
specification. I shall update regarding this and share my experience.
>
>
>> Now I have been looking at this
>> http://www.alsa-project.org/main/index.php/Tutorials_and_Presentations.
>>
>> With thanks
>> Sathishkumar
>>
>>
> --
> William G. Unruh | Canadian Institute for| Tel: +1(604)822-3273
> Physics&Astronomy | Advanced Research | Fax: +1(604)822-5324
> UBC, Vancouver,BC | Program in Cosmology | [email protected]
> Canada V6T 1Z1 | and Gravity | www.theory.physics.ubc.ca/
>
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