I played it out of my laptop speaker and picked it with my laptop mic.
Surprisingly (or maybe not for some) the second half comes back some 5 times
stronger in partial amplitudes than the first half. I have not observed any
additional harmonic. I assume that shows speaker distortion is not an issue
here.
I don't hear them as pitched sounds. The first sounds a pulse train and the
second sounds a noise repeating itself. Though man is expected to hear down
to 20hz I seem to remember that pitch perception doesn't go that deep.
For human ears the usual auditory model uses autocorrelation. With that
you'll have a 30hz entry with or without a 30hz tone.
Xue
-----Original Message-----
From: Didier Dambrin
Sent: Thursday, December 06, 2012 10:27 AM
To: A discussion list for music-related DSP
Subject: Re: [music-dsp] Ghost tone
Mmmh can you explain why it's there (where it's from, I mean, this would
mean that out of the same harmonics, just with different phase relationship,
very low tones could be produced?), & how to see it?
I got another reply suggesting it's due to the ear's compressor, & that
seems more belieable, also explains why it doesn't happen with the other,
more continuous version. The gap between peak would suggest a tone around
30hz, which could really be it. It would also imply that the ear's
compression has a very short attack/release time, for the "compression
envelope" pulsating fast enough to be in the audible range.
-----Message d'origine-----
From: Thomas Young
Sent: Thursday, December 06, 2012 11:20 AM
To: A discussion list for music-related DSP
Subject: Re: [music-dsp] Ghost tone
1) The low frequencies are audible
2) It's not speaker distortion, the low frequencies are present in the
signal
I think the spectrum of the first signal can be a bit misleading, if you are
a bit more selective about where you take the spectrum (i.e. between the
asymptotic sections) the low frequency contribution is easier to see.
The unpleasant "pressure" effect is exactly that, sound pressure waves. The
strength will be dependent on the acoustics of your environment, it will be
particularly objectionable if your ears happen to be somewhere where a lot
of the wavefronts collide. The proximity of headphones to your ears is no
doubt exacerbating the effect, especially in the very low frequencies which
would otherwise bounce all over the place and diffuse.
Mics generally won't pick up very low frequencies - or more accurately their
sensitivity to lower frequencies is very low.
-----Original Message-----
From: music-dsp-boun...@music.columbia.edu
[mailto:music-dsp-boun...@music.columbia.edu] On Behalf Of Didier Dambrin
Sent: 06 December 2012 05:50
To: A discussion list for music-related DSP
Subject: [music-dsp] Ghost tone
Hi,
Here's something to listen to:
http://flstudio.image-line.com/help/publicfiles_gol/GhostTone.wav
It's divided in 2 parts, the same bunch of sine harmonics in the upper
range, only difference is the phase alignment. (both will appear similar
through a spectrogram)
Disregarding the difference in sound in the upper range, 1. anyone confirms
the very low tone is very audible in the first half?
2. (anyone confirms it's not speaker distortion?) 3. anyone knows about
litterature about the phenomenon?
While I can understand where the "ghost tone" is from, I don't understand
why it's audible. I happen to have hyperacusis & can't stand the low traffic
rumbling here around, and I was wondering why mics weren't picking it, as I
perceive it very loud. I hadn't been able to resynthesize a tone as nasty
until now, mainly because I was trying low tones alone, and I can't hear
simple sines under 20Hz.
The question is why do we(?) hear it, why is so much "pressure" noticable
(can anyone stand it through headphones? I find the pressure effect very
disturbing).
Strangely enough, I find the tone a lot more audible when (through
headphones) it goes to both hears, not if it's only left or right.
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