There is a peculiar phenomenon with "strict" repetitive electronic sounds that I noticed a few times. When listening to these sounds for prolonged durations (a minute or two suffice) via headphones, then turning them off, all your "natural" acoustic environment has a strange modulation to it. E.g. with the following sound, the acoustic "after image" I have is some "bubbly" or "fft-ish" modulation of my environment. Guess it's a neural-physiological thing: (try with loop)


My colleague confirmed this impression; seems to require closed headphones. My theory is that we "hear" a spectrally complementary function, for example notches when there where strong partials, similar to how we see negative afterimages when we look at a static image for a while and then move the eyes to something else.

There is a reference from German psycho-acoustician Zwicker about an "acoustical aftertone", describes as sine components after prolonged hearing of a notched noise.

@sciss yes! I know exactly what you are talking about. I thought I was the only one, and was too scared to talk about it.

@paul @sciss me too, I noticed it first with Pd and assumed it was caused by too high volume or bad interpolation causing artifacts to linger after the sound has ended, but the complementary aftertone idea makes much more sense. perhaps this could be exploited for artistic effect...

@mathr @sciss Absolutely! A friend of mine does this something similar with things called "auditory distortion products", which can weird inner-ear modulations to happen. His compositions can be really trippy to listen to. A while ago he made some software for it:

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