title: C/C++/Obj-C Real-time algorithm to ascertain Note (not Pitch) from Vocal Input
body: <p>I want to detect not the pitch,  but the <strong>pitch class</strong> of a sung note.</p>
  
  <p>So,  whether it is C4 or C5 is not important: they must both be detected as C.</p>
  
  <p>Imagine the 12  semitones arranged on a clock face,  with the needle pointing to the pitch class.   That's what I'm after! ideally I would like to be able to tell whether the sung note is spot-on or slightly off.</p>
  
  <p>This is not a duplicate of previously asked questions, as it introduces the constraints that:  </p>
  
  <ol>
  <li><p>the sound source is a <strong>single human voice</strong>,  hopefully with negligible background interference (although I may need to deal with this)</p></li>
  <li><p>the octave is not important, <strong>only the pitch class</strong></p></li>
  </ol>
  
  <p>EDIT -- Links:<br>
  <a href="https://stackoverflow.com/questions/1354084/real-time-pitch-detection?lq=1">Real time pitch detection</a><br>
  <a href="https://stackoverflow.com/questions/3398753/using-the-apple-fft-and-accelerate-framework?lq=1">Using the Apple FFT and Accelerate Framework</a></p>