Real Time Audio Analysis In Linux

This guide should help. Don't use ALSA for your application. Use a higher level API. If you decide you'd like to use JACK, http://jackaudio.org/applications has three instrument tuners you can use as example code.

Marsyas would be a great choice for doing this, it's built for exactly this kind of task.

For tuning an instrument, what you need to do is to have an algorithm that estimates the fundamentalfrequency (F0) of a sound. There are a number of algorithms to do this, one of the newest and bestis the YIN algorithm, which was developed by Alain de Cheveigne. I recently added the YIN algorithmto Marsyas, and using it is dead simple.

Here's the basic code that you would use in Marsyas:

  MarSystemManager mng;  // A series to contain everything  MarSystem* net = mng.create("Series", "series");  // Process the data from the SoundFileSource with AubioYin  net->addMarSystem(mng.create("SoundFileSource", "src"));  net->addMarSystem(mng.create("ShiftInput", "si"));  net->addMarSystem(mng.create("AubioYin", "yin"));  net->updctrl("SoundFileSource/src/mrs_string/filename",inAudioFileName);  while (net->getctrl("SoundFileSource/src/mrs_bool/notEmpty")->to<mrs_bool>()) {    net->tick();    realvec r = net->getctrl("mrs_realvec/processedData")->to<mrs_realvec>();    cout << r(0,0) << endl;  }

This code first creates a Series object that we will add components to. In a Series, each of the componentsreceives the output of the previous MarSystem in serial. We then add a SoundFileSource, which you can feedin a .wav or .mp3 file into. We then add the ShiftInput object which outputs overlapping chunks of audio, whichare then fed into the AubioYin object, which estimates the fundamental frequency of that chunk of audio.

We then tell the SoundFileSource that we want to read the file inAudioFileName.

The while statement then loops until the SoundFileSource runs out of data. Inside the whileloop, we take the data that the network has processed and output the (0,0) element, which is thefundamental frequency estimate.

This is even easier when you use the Python bindings for Marsyas.

http://clam-project.org/ CLAM is a full-fledged software framework for research and application development in the Audio and Music Domain. It offers a conceptual model as well as tools for the analysis, synthesis and processing of audio signals.

They have a great API, nice GUI and a few finished apps where you can see everything.