wessberg/libKeyFinder

Musical key detection for digital audio, GPL v3

libKeyFinder

libKeyFinder can be used to estimate the musical key of digital recordings.

It is the basis of the KeyFinder GUI app, which is available as a binary download for Mac OSX and Windows at www.ibrahimshaath.co.uk/keyfinder

Examples

For the most basic use case, do something like this:

// Static because it retains useful resources for repeat use
static KeyFinder::KeyFinder k;

// Build an empty audio object
KeyFinder::AudioData a;

// Prepare the object for your audio stream
a.setFrameRate(yourAudioStream.framerate);
a.setChannels(yourAudioStream.channels);
a.addToSampleCount(yourAudioStream.length);

// Copy your audio into the object
for (int i = 0; i < yourAudioStream.length; i++) {
  a.setSample(i, yourAudioStream[i]);
}

// Run the analysis
KeyFinder::KeyDetectionResult r =  k.keyOfAudio(a);

// And do something with the result
doSomethingWith(r.globalKeyEstimate);

Alternatively, you can transform a stream of audio into a chromatic representation, and make progressive estimates of the key:

KeyFinder::AudioData a;
a.setFrameRate(yourAudioStream.framerate);
a.setChannels(yourAudioStream.channels);
a.addToSampleCount(yourAudioStream.packetLength);

static KeyFinder::KeyFinder k;

// the workspace holds the memory allocations for analysis of a single track
KeyFinder::Workspace w;

while (someType yourPacket = newAudioPacket()) {

  for (int i = 0; i < yourPacket.length; i++) {
    a.setSample(i, yourPacket[i]);
  }
  k.progressiveChromagram(a, w);

  // if you want to grab progressive key estimates...
  KeyFinder::KeyDetectionResult r = k.keyOfChromagram(w);
  doSomethingWithMostRecentKeyEstimate(r.globalKeyEstimate);
}

// if you only want a single key estimate, or to squeeze
// every last bit of audio from the working buffer after 
// progressive estimates...
k.finalChromagram(w);

// and finally...
KeyFinder::KeyDetectionResult r = k.keyOfChromagram(w);

doSomethingWithFinalKeyEstimate(r.globalKeyEstimate);

Installation

First, you will need to install libKeyFinder's dependencies:

• FFTW version 3

  OSX and homebrew: $ brew install fftw

Once dependencies are installed, build libKeyFinder:

$ mkdir build
$ cmake -DCMAKE_INSTALL_PREFIX /where/you/want/to/install/to -S . -B build
$ cmake --build build --target install --parallel number-of-cpu-cores

If you want to build libKeyFinder statically, add -DBUILD_STATIC_LIBS to the first call to cmake above.

Testing

The tests are built together with the library. Simply run the test executable from the build directory:

$ build/tests/test

If all goes well, you should see something like this:

===============================================================================
All tests passed (1705510 assertions in 65 test cases)

Note that there is a known intermittent failure in the FftAdapterTest/ForwardAndBackward test. Try running the tests a handful of times to determine whether you are hitting the intermittent or have introduced a new bug.