C/C++/Obj-C Real-time algorithm to ascertain Note (not Pitch) from Vocal Input

Question

I want to detect not the pitch, but the pitch class of a sung note.

So, whether it is C4 or C5 is not important: they must both be detected as C.<

Answer 1

Most of the frequency detection algorithms cited in other answers don't work well for voice. To see why this is so intuitively, consider that all the vowels in a language can be sung at one particular note. Even though all those vowels have very different frequency content, they would all have to be detected as the same note. Any note detection algorithm for voices must take this into account somehow. Furthermore, human speech and song contains many fricatives, many of which have no implicit pitch in them.

In the generic (non voice case) the feature you are looking for is called the chroma feature and there is a fairly large body of work on the subject. It is equivalently known as the harmonic pitch class profile. The original reference paper on the concept is Tayuka Fujishima's "Real-Time Chord Recognition of Musical Sound: A System Using Common Lisp Music". The Wikipedia entry has an overview of a more modern variant of the algorithm. There are a bunch of free papers and MATLAB implementations of chroma feature detection.

However, since you are focusing on the human voice only, and since the human voice naturally contains tons of overtones, what you are practically looking for in this specific scenario is a fundamental frequency detection algorithm, or f0 detection algorithm. There are several such algorithms explicitly tuned for voice. Also, here is a widely cited algorithm that works on multiple voices at once. You'd then check the detected frequency against the equal-tempered scale and then find the closest match.

Since I suspect that you're trying to build a pitch detector and/or corrector a la Autotune, you may want to use M. Morise's excellent WORLD implementation, which permits fast and good quality detection and modification of f0 on voice streams.

Lastly, be aware that there are only a few vocal pitch detectors that work well within the vocal fry register. Almost all of them, including WORLD, fail on vocal fry as well as very low voices. A number of papers refer to vocal fry as "creaky voice" and have developed specific algorithms to help with that type of voice input specifically.