segments_pitches: What are the units?

[James Suruda]

All-

I am trying to understand the meaning of the segments_pitches field in h5 files from the MSD, and am hoping that someone here understands the units and might explain or post a link to documentation.  I have been unsuccessful in finding my answer with Google...

segments_pitches is a 2-dimensional array of pitches (tones, sound frequencies), yes?   Familiar presentations of pitch for me are things like "440.1Hz" or "C3".  But data in the MSD for this field is in the form of floating point numbers between 0 and 1.  For example, the Dinosaur Jr. song I am looking at starts off with these pitches:

(0,0): 0.931, 0.858, 0.898, 0.842, 0.823, 0.726, 0.891, 0.915, 1,

(0,9): 0.97, 0.741, 0.71,

Does .931 represent a sound of a certain frequency?    What frequency is that?   And does a .931 in this file mean the same as a .931 in another file?   I'm also unsure what (0,9) means but if I can find a way to translate .898 into a frequency I will be pretty happy :)

Thanks in advance for any help, I do appreciate it!

Jim Suruda
Computer Science
Southern Illinois University
615.438.1277

[Thierry Bertin-Mahieux]

Hi Jim,
the Echo Nest pitches are often called chroma features in the music tech literature.
The idea is to cut a spectrogram in bands that correspond to the music semitones (A, ...., G#)

More specifically, the chroma bin for A contains the sum of the energy of all the frequency bands that correspond to A.
To normalize, The Echo Nest simply divides by the max value, so the max is always 1.

Here is a tech doc from The Echo Nest, accessible through their API
http://developer.echonest.com/docs/v4/track.html#analyze
http://developer.echonest.com/docs/v4/_static/AnalyzeDocumentation.pdf
Plot from page 5 shows you that the first value is C, the last one B.

If it helps, here is some explanation / code to compute chroma features from another source:
http://labrosa.ee.columbia.edu/matlab/chroma-ansyn/

Cheers!
Thierry

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Thierry Bertin-Mahieux
Columbia University, NY
Ph.D. Candidate, Electrical Engineering
http://www.columbia.edu/~tb2332/