Phantom fundamentals

[Chris Ford]

Hi all,

I'm in the awkward situation of trying to build an aural illusion and being uncertain of whether or not I've succeeded. A phantom fundamental is when you omit the fundamental frequency, but the brain reconstructs it using the harmonics.

I've tried to put together a simple demonstration of this using a simplified version of Jen Smith's bell. Ideally, the following two invocations of the bell should sound like they're the same note:

(bell 300 20.0)          ; Ring bell at 300hz for 20 seconds

(bell 300 20.0 0.0)    ; Ring bell at 300hz for 20 seconds, omitting the fundamental

Does this work for anyone? I would expect the latter to sound "thinner" and softer, even if the illusion succeeds.

Cheers,

Chris

[Roger Allen]

Trying with a fundamental of 600Hz, the bells sounds different to me.  On my laptop, your original fundamental is too soft to hear.  A (demo (sin-osc 300)) is barely audible while 400Hz & higher is easier to hear.

You could also do an FFT & display the values in a spectrogram.  I don't know how to do that from within Overtone, but you can use Audacity.

Cheers,

Roger

[Matthew Gilliard]

> You could also do an FFT & display the values in a spectrogram. I don't
> know how to do that from within Overtone, but you can use Audacity.

On linux I've used freqtweak - plugged into jack between supercollider
and the hardware master-out. I found it worked well, and was pretty
handy.

Matthew

http://freqtweak.sourceforge.net/

[Chris Ford]

As I understand the illusion, it's not expected to sound exactly the same but a not with and without the fundamental is supposed to be identified as "the same" by the brain.

I would expect the version without the fundamental to be quieter, feel "thinner" and have slightly more prominent interaction between the higher harmonics.

Example on YouTube

Chris

[Giwrgos Andris]

Hey I have recently started to study about Music Production and I can't understand this term of phantom fundamental. If this is the exact term:
"A phantom fundamental is when you omit the fundamental frequency, but the brain reconstructs it using the harmonics.", why would we want to creat such "thing"/sound? I mean what use does this have? For us its the same thing, right? We hear the exact same thing, regardless having the fundamental frequency...

[Gary Trakhman]

It happens naturally in brass instruments an octave below the fundamental frequency, it's called a pedal tone.  Your lips are in fact vibrating at the fundamental, but only overtones are making it through the instrument.

http://en.wikipedia.org/wiki/Pedal_tone

Another reason to have a phantom fundamental is when you care about the actual speaker throw and potential nonlinearity of bass.  You can conserve energy and movement of the cone without significantly altering perception.  I believe I've seen signal-processing boxes that do just that, though I can't find one right now.

On Fri, Feb 7, 2014 at 11:58 AM, Giwrgos Andris <geo.a...@gmail.com> wrote:

Hey I have recently started to study about Music Production and I can't understand this term of phantom fundamental. If this is the exact term:
"A phantom fundamental is when you omit the fundamental frequency, but the brain reconstructs it using the harmonics.", why would we want to creat such "thing"/sound? I mean what use does this have? For us its the same thing, right? We hear the exact same thing, regardless having the fundamental frequency...

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[Marmaduke Woodman]

There is a nonlinear response in the cochlea to different intervals. A set of hair cells actually feed back into the system, and the frequencies interact.

I'm not makign this up, in this paper, Figure 1, you can see that the response from the auditory system has huge responses that are not in the stimulus, and their model reproduces this as well.

We could add that to Overtone, as well, because their tonal perception model is just another equation. That might help programming an aural illusion.