Pure sine wave?

[PeteMcK]

At http://headwize.com/projects/showfil...meier5_prj.htm
Jan Meier says this:
“Mechanical harmonic distortion in the inner ear: A pure 200 Hz sine wave not only makes the basillary membrane inside the ear vibrate at 200 Hz, but also at 400, 600, 800, 1000, 1200.... Hz. For sine waves between 200 and 3000 Hz these overtones have amplitudes of 33%, 13%, 6%, 4%, 2%, .... of the amplitude of the fundamental. Harmonic distortion in the inner-ear thus sums up to approximately 60%! Nonetheless, we only hear a pure sine-wave at the fundamental frequency since our brain has learned that this specific frequency spectrum belongs to a pure tone.”

This made me wonder if it was possible to create a waveform which would let us perceive only the fundamental, and if so what that waveform would look like?
Pete McK

[454Casull]

Nonetheless, we only hear a pure sine-wave at the fundamental frequency

Doesn't this mean that we ALREADY hear a fundamental frequency when one is played? The brain filters out the harmonics that the ear produces.

[PeteMcK]

then how about a waveform that would excite only the fundamental?

[Paradise_Ice]

I think i know what your trying to say, but i dont have an answer,
an audiologist would have some kind of answer am sure, if it made sense is another thing, I really cant imagine what the wave would look like?

[454Casull]

Originally posted by PeteMcK
then how about a waveform that would excite only the fundamental?

I'm thinking a waveform with harmonics of a negative amplitude (the pressure, anyway) might do it, but that's impossible.

[joe carrow]

Originally posted by 454Casull

I'm thinking a waveform with harmonics of a negative amplitude (the pressure, anyway) might do it, but that's impossible.

The lens in your eye projects an image on your retina that is upside down. Your brain corrects this and you never notice. Special glasses can flip it right side up (everything looks upside down)

I think you'd hear the missing harmonics like they're there. I don't think that this is something we need to worry about for HiFi, but it could be a consideration for cochlear implants or a future technology with direct connections to the brain!

-Joe

PS- I wrote more, but "check message length" tells me that this is over 10,000 characters!

EDIT: I completely misread the message that popped up. It was a little on the long side, and I thought that since I was new I might have some sort of introductory message length limit. What I was saying, though, is that with a wave "negative" would just mean "out of phase". So yes- I think that it's reasonably possible, if you studied an ear enough, to create a waveform that would produce a single fundamental at a given point. Of course, IIRC, the ear is a complicated thing and the part that converts motion to nerve impulses is not a single point.

[johninCR]

You create the harmonic overtones and this makes you hear the fundamental without it being played. That's how several of the bass enhancement products like MaxxBass and others create the audio illusion of bass frequencies with drivers that won't play those low frequencies. The problem is that since those low frequencies aren't really played, you can't feel them so it doesn't sound quite real.

[mikee12345]

Originally posted by johninCR
You create the harmonic overtones and this makes you hear the fundamental without it being played. That's how several of the bass enhancement products like MaxxBass and others create the audio illusion of bass frequencies with drivers that won't play those low frequencies. The problem is that since those low frequencies aren't really played, you can't feel them so it doesn't sound quite real.

Certainly! perception and reality can be rather different things.
I downloaded a 'sub harmonic synthesiser' that adds 'lower bass'.Infact,all it does is make sinewaves more like square!

[leftnote]

>then how about a waveform that would excite only the >fundamental?

That's a nice idea.

One has to think about the way sound excites the membrane of the ear. To greatly simplify things one can consider a string with fixed endpoints e.g. a guitar string. If you were able to deform the string in a perfect half wavelength shape then release it I believe you would have no harmonics. However, if you were to pluck it at a point you would get all sorts of travelling waves. Some of those travelling waves, however would superimpose on opposite travelling ones just right to cause standing waves i.e. resonance at various harmonics. These waves eventually die away due to internal losses e.g. friction.

So you could try two things: you could either try to stick somethings in your ear which only excites the 'fundamental' or you could try to supress the membrane from vibrating at harmonics. Perhaps this would be possible by playing tones at the harmonics which are '180 deg' out of phase with the 'fundamental', by this I mean that when the 'fundamental' is pressure maximum, the supression tone reaches pressure minimum. However this depends on exactly how sound pressure excites the tympanic membrane. You could have the opposite effect!

Once could easily do audio experiments to see if the brain filters this stuff out.

[janneman]

Originally posted by mikee12345




Certainly! perception and reality can be rather different things.
I downloaded a 'sub harmonic synthesiser' that adds 'lower bass'.Infact,all it does is make sinewaves more like square!

Sinewaves that start to look like squares means that they have harmonics being added, specifically odd harmonics. If you add even harmonics the sine will start to look like traingle waves. Of course, for perfect square waves or triangles the harmonics need to have a specific level ratio to the carrier.

Jan Didden