Guys, thanks so much for your posts!!!
And macegr, thanks to answer also here
I think that the best thing is to try to explain you what I am doing.
I am trying to support a project of an electronic musician.
We are building an electronic instrument that should act as controller for live perfomance.
In particular we would like to acquire the signal produced by "playing"/"touching" four cords. The musician think that using simply headphones to acquire the signal can be enough. He tested heaphones with the input line of a standard audio card and they seems to provide a good signal for his purpose.
Actually I did not understand exactly what information about the audio signal he want; I am waiting for a clarification. Up to now, I think he need a "envelope follower".
The controller includes various sensors (for example membrane potentiometers), for this reason we are already using Arduino.
The general architecture I proposed uses Arduino as simply hardware controller to acquire the sensor data; all the needed computations are done by a PC connected to Arduino, running a specific MAX/MSP controlling patch.
As you think, I proposed him to use an external audio card to acquire the signal from headphones; however for packing considerations (to reduce the number of connections and requirements to use the controller from a PC) he asked me if we could use Arduino for such purpose (because we are already using it). Links like thishttp://interface.khm.de/index.php/lab/experiments/arduino-realtime-audio-processing/
let me think that it is possibile to read the raw signal from arduino...
but according to your posts, it seems that if I need to sample accurately the signal, this can't be done with Arduino due to its limited computational capabilities.
Finally, the musician told me that the following shield should provide what he needshttp://www.andregoncalves.info/ag_blog/?page_id=61
I will ask to the musician what he exactly needs respect to the audio signal. And then I will write the answer here!
Thanks so much again guys!!!