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In Reply to: Re: Hiraga on Feedback posted by Scott Frankland on May 14, 2003 at 14:47:53:
I might throw this in: Music is composed of multiple tones that generate IM as well as harmonic distortion. These simple tone tests that use only ONE major tone will be incorrect in what level is actually masked, because the IM tones can be anywhere. However, before everyone gets excited, it should be noted that musical chords IM in tune with the other notes. How about that? This could provide a further argument that higher order odd harmonics could be heard, even below the so called 'masking level' because the IM byproducts would make them accessable to the the ear.
Follow Ups:
Hi,An example of what you mean by "it should be noted that musical
chords IM in tune with the other notes." I'm not following you.The reason you lost me is because IM is a beat frequency with a
string of harmonics. These harmonics are multiples of the beat
frequency. Since we have seen that harmonics of a fundamental are
out of tune with their nearest note neighbors, why would IM
harmonics be in tune with their note neighbors?
Yes, there is a whole lotta blending goin' on. I agree that the single-tone case lacks precision when applied to the multitone case, but in its favor the single-tone case allows us to get a grip on the fundamentals.Besides bringing out strident intervals it's also possible for musical IM to *mask* them. To quote myself again: "The blending effect can be easily tested with a guitar. For example, playing F (below open E) together with open E causes objectionable beating. Adding an A intermediate to the two tones smoothes out the subjective effect considerably. The interval of F with E is a major seventh (8:15). Adding the A, however, creates two new intervals: a major third (4:5) and a perfect fifth (2:3). The two consonant intervals then "swamp out" the one dissonant interval to create an overall composite consonance. The critical parameter for composite consonance is thus not masking, but blending."
I am saying here what you are saying, John, that even a slight out of tune or out of phase resonance or IM can throw off an otherwise consonant blend of sounds. The masking effect is a small part of this equation, which equation I think is far more complicated than Cheever makes it out to be. Consonance or dissonance are the result of the composite waveform as it strikes the ear, and this includes room effects.
There is a paper in the AES preprint 'INTERMODULATION DISTORTION IN TAPE RECORDING' Robert Z Langevin, Ampex Oct . 1962. This paper shows that the IM generated by the same non-linearity as that that produces either 2'nd or 3'rd harmonic distortion will still be coincident to the music being played. Basically, if the order of harmonic distortion is low, the IM products will generally be OK in the musical selection. It would seem to me that higher order IM products would be just as bad as higher order harmonic products, but even more obvious in many cases.
John, I think you are right. I'm just pointing out a counterinstance. Although it *is* possible to mask high-order distortion via specific modes of IM blending (as my guitar experiment will show), it is also more unlikely to happen during music program. Cheers.
Scott, or anyone else, if you want a copy of the Langevin IM paper, I can send it by e-mail. Just send me your e-mail address to: j_curl@earthlink.net Unfortunately, without a website, I can't link it here.
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