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:
https://open.audio/library/tracks/42838/ (try with loop)
scalacollider-code for that sound:
val freq0 = Seq(1.0, 1.02).map(_ * 8.824352)
val freq2 = Seq(1.0, 0.994).map(_ * 7860.8604)
val xi = LFSaw.ar(freq = freq0, iphase = 0.0)
val freq_0 = xi clip2 0.011223611
val lFDNoise3 = LFDNoise3.ar(freq_0)
val cuspN = CuspN.ar(freq = freq2, a = 1.0, b = 0.0, xi = xi)
val mix = Mix(lFDNoise3, cuspN))
val sig = Limiter.ar(LeakDC.ar(mix.clip2(1.0)) * 0.5)
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.
Auditory afterimage (neurological explanation): https://www.brainnrg.org/files/publicationmodule/@random45f5724eba2f8/pid1799.pdf
Also about the metallic effects: https://asa.scitation.org/doi/full/10.1121/1.2828057
@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: http://alexchechile.com/projects.html