Subject: Chroma perception; was: Robust method of fundamental frequency estimation. From: Martin Braun <nombraun@xxxxxxxx> Date: Sun, 4 Feb 2007 14:19:35 +0100 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>Dear Pierre, Arturo, Rob, and others, on Friday, 2 Feb, Pierre Divenyi raised this question: "What is the most remarkable, and still begging for explanation (which should be difficult to obtain experimentally because it tackles a subjective dimension), is the subjective smoothness of a descending scale played on any of the low-pitched instruments, despite the lack of smoothness when you play only a sinusoid." At least there is now a good candidate for an "explanation": chroma perception (also called pitch class perception). Anatomical and physiological evidence indicates that the mammalian auditory brain carries out chroma filtering in the ventral division of the medial geniculate nucleus (MGN) of the thalamus. For this reason, tones from musical instruments around C1 (32.7 Hz) can be well identified, even when a periodicity at this frequency is absent. Information from octave spaced harmonics C2, C3, etc. is always present. And most importantly, it usually is the strongest component of all octave-spaced sound energy of the tone. Octave spaced signals are assumed to be integrated and extracted in the thalamus, thus forming the basis of chroma perception. So, if the f0 at C1 on the piano is fuzzy or absent, our brain still perceives the chroma of C. In combination with the available timbre information it then can easily attribute the pitch of C1 to the sound. Musician, and presumably most non-musicians as well, have no problems hearing the difference between C1 and C#1 from natural sounds of musical instruments. The relevant anatomical and physiological evidence is listed here: http://web.telia.com/~u57011259/Wright.htm Martin --------------------------------------------------------------------- Martin Braun Neuroscience of Music S-671 95 Klässbol Sweden web site: http://w1.570.telia.com/~u57011259/index.htm