Skip to main content ↑ ↓

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: Psychoacoustic Effects of High Freqencies (Read 9609 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

Psychoacoustic Effects of High Freqencies

Hello, I'm new to the forum! =]

but anyway...

I noticed something when playing back high frequency tones and am unsure if it is a psychoacoustic affect, or if it has more to do with sound in the physical world. 

Using speakers and NOT headphones,  I swept through a range of high frequencies and noticed how I would perceive the arrival of different frequencies in different ears.  Another effect became even more intriguing that this.   Leaving the frequency control alone (so just playing a sine wave at around 11KHz) I then I realized that when I moved my head (left to right, up and down etc) I could move it to an exact position where I can no longer hear fixed frequencies in a certain ear at all.  It was as if the sound waves were a physical presence at precise locations in the room, so depending on where I moved my head, I would be 'receiving' the frequencies in my ear, or not receive them at all. 

You can try these things yourself if you take a sine wave oscillator and gradually ramp up the frequency from say 9KHz and up (it works for all high frequencies really).  You may notice the effect of different frequencies arriving at different ears as you ramp up (a panning effect).   The other effect with a single unchanging frequency is very noticeable to me at around 11-12KHz, and I did this with laptop speakers so anything will do.  Just make sure to crank up the volume!  So try playing an 11KHz tone really loud, and just move your head around slowly - you should notice the perceived intensity of that frequency falling and rising.  In reality it sounds 'wibbly' because the rising and falling happens so frequently as you move your head even very slowly. 

Any explanations for this?  I have my own theories but I thought I should check first whether this effect is widely understood.  

Re: Psychoacoustic Effects of High Freqencies

Reply #1 –
Quote from: echogecko on
Any explanations for this?  I have my own theories but I thought I should check first whether this effect is widely understood.  

Yes, that would be the effect of the acoustics in your room. 

Re: Psychoacoustic Effects of High Freqencies

Reply #2 –
Yep, I know that phenomenon perfectly well. It's not primarily a psychoacoustic effect (in fact, as you will soon understand, rather the absence of one) but the physical effect the shape of your outer and inner ear has on high frequencies, i.e. the resonances they create, amplifying or muting very narrow frequency bands depending on the exact direction of the source. This is simply the way our ears enable us to spatially (three-dimensionally) locate a sound despite having only two of them available. Our brain computes the exact signature shaped by our ears in order to locate the sound, but this works only for complex "natural" signals with plenty of spectral information. There is no way to detect such a signature from a pure sine wave signal, so our psychoacoustic "algorithms" fail and instead of hearing the signal coming from a certain point in space, all we hear is the sine wave changing its volume as it resonates within our ear.

Re: Psychoacoustic Effects of High Freqencies

Reply #3 –
Quote from: saratoga on
Yes, that would be the effect of the acoustics in your room. 
That further complicates it of course, but I think what the OP describes can essentially be attributed to ear resonances.

Re: Psychoacoustic Effects of High Freqencies

Reply #5 –
Quote from: greynol on
Resonances do not cause cancellation (which is also what is being described).
True, but what you perceive as a "cancellation" may simply be the high frequency singal falling below your hearing threshold...

Re: Psychoacoustic Effects of High Freqencies

Reply #6 –
Yes, resulting from partial cancellation due to multiple reflections.

You can get the same result recording with a microphone (no ear resonances necessary!).

Re: Psychoacoustic Effects of High Freqencies

Reply #7 –
I don't doubt that, although the higher the frequency the less room resonances you generally experience.

However, I'm pretty sure that the effect the OP describes at the given frequencies around 10 kHz is primarily due to ear resonances.

Re: Psychoacoustic Effects of High Freqencies

Reply #9 –
...but again, they enable you to hear stuff that would otherwise fall below your hearing threshold ;)

Re: Psychoacoustic Effects of High Freqencies

Reply #11 –
OK, please forgive my imprecise terminology. I vow to explicitly write resonances/interferences whenever I'm referring to something that's actually a combination of both phenomena from now on O:)

Re: Psychoacoustic Effects of High Freqencies

Reply #12 –
It just seemed to me that you were dismissing a portion of the equation as if it had no influence (acoustic reflections).

Now maybe the OP is doing this outside or in an anechoic chamber in which case you can be more certain that it doesn't.

Re: Psychoacoustic Effects of High Freqencies

Reply #13 –
Quote from: Northpack on
...but again, they enable you to hear stuff that would otherwise fall below your hearing threshold ;)

The frequencies I'm playing back are definitely well above my hearing threshold.  It is quite difficult to move my head to the precise point where I no longer hear the sound, and even at that, the sound only becomes absent in one ear.  My understanding of acoustics isn't great but to me it seems like there is literally no sound entering my ear under these circumstances, so I thought that perhaps the build up of room reflections were so laser focused in direction that there would be spaces in the room where sound just isn't traveling or has decayed below the threshold of hearing.  My head could be blocking the sound on one side so that the other side of my head does not catch reflections precisely into my ear.  This idea would at least explain why the effect is so pronounced in higher frequencies, because we know them to be more easily absorbed by physical materials such as my head. 

To clarify, I did this in my bedroom which is about 8x10ft with quite a lot of wood, but just as much soft stuff like curtains, bedding etc.  I have not yet tried this in different areas of the room with any regard to these factors. 

Quote from: Northpack on
Yep, I know that phenomenon perfectly well. It's not primarily a psychoacoustic effect (in fact, as you will soon understand, rather the absence of one) but the physical effect the shape of your outer and inner ear has on high frequencies, i.e. the resonances they create, amplifying or muting very narrow frequency bands depending on the exact direction of the source. This is simply the way our ears enable us to spatially (three-dimensionally) locate a sound despite having only two of them available. Our brain computes the exact signature shaped by our ears in order to locate the sound, but this works only for complex "natural" signals with plenty of spectral information. There is no way to detect such a signature from a pure sine wave signal, so our psychoacoustic "algorithms" fail and instead of hearing the signal coming from a certain point in space, all we hear is the sine wave changing its volume as it resonates within our ear.

This makes sense of the panning effect I think.

Re: Psychoacoustic Effects of High Freqencies

Reply #14 –
Are you listening in stereo (i.e. the same tone is coming out of both speakers)?

Re: Psychoacoustic Effects of High Freqencies

Reply #15 –
Quote from: drewfx on
Are you listening in stereo (i.e. the same tone is coming out of both speakers)?

Yes.  I have the same mono signal going to both laptop speakers.

Re: Psychoacoustic Effects of High Freqencies

Reply #16 –
Quote from: echogecko on
Yes.  I have the same mono signal going to both laptop speakers.

The effect you hear is known as "interference".

Did you ever use a "ripple tank" (real or virtual) in school physics? Consider what you see when you drop two rocks into a pond. The waves from each radiate out. When they cross, they form patterns. Where the two waves are both going "up" or "down" as they cross, at that spot they make a taller peak or trough. When one is going "up" and the other "down", they cancel out to leave a flat spot. The same thing happens with sound. Sound wavess are alternate high and low pressure zones that radiate out from the source at the speed of sound. You have two identical sources. If two high pressure zones arrive at your ear at the same time, you hear the sound. If a high pressure and low pressure zone arrive at the same time, they cancel each other and you don't hear it. Moving your head alters the relative time delay from the two laptop speakers to your ear, moving it from a place where the sounds add to a place where they cancel.

There's a wikipedia page:
https://en.wikipedia.org/wiki/Interference_(wave_propagation)

This image on the page illustrates the process.
https://upload.wikimedia.org/wikipedia/commons/2/2c/Two_sources_interference.gif
You can see the zones where the waves add and where they cancel.

Regards,
   Don Hills
"People hear what they see." - Doris Day

Re: Psychoacoustic Effects of High Freqencies

Reply #17 –
Quote
or if it has more to do with sound in the physical world. 

Using speakers and NOT headphones...
That's a big clue that it's related to the way the waves are mixing in the air.   If you've ever tried inverting one channel (or reversing the wires to one speaker) you'll get lots of cancellation that changes as you move around, and a spacey-phasey sound (and almost all of the bass sound waves will cancel but of course you won't notice that with laptop speakers).    But, if you play the inverted sound through headphones you might not notice anything at all.

A 10kHz wave has a wavelength of about 1.5 inches so ignoring reflections, if one speaker is 3/4th's of an inch closer to your ear than the other, the waves will be out-of-phase and cancel.

Re: Psychoacoustic Effects of High Freqencies

Reply #19 –
Just use one speaker.
EZ CD Audio Converter

Re: Psychoacoustic Effects of High Freqencies

Reply #20 –
I agree that if you play the signal on two speakers, the effects are likely due to interference from the two sources.

Re: Psychoacoustic Effects of High Freqencies

Reply #21 –
North pack's original answer plus the interference effect of cancellation at intersecting nodes are correct. but there is at least 1 other factor which is your head effect itself - size, shape of your head & your ears position on them. The head creates a "sound shadow" and the resulting attenuation of sound is another key ingredient in the brain's algorithm for spatial location. In addition, pinnae position, angle & shape of convolutions all modify any sound U hear. Your experiment with a pure sine wave tone is a rare instance where so many other "messy aspects" of incoming sound are eliminated. Normally, the small differences U observed are completely obfuscated by real-world of extremely complex, overlapping waveforms.
To see how variable your effect is, try the following...use mono with 1 speaker, mono with 2 speakers; use better speakers, move farther back from speakers, change rooms; and [you'll look funny] use your fingers to flatten your pinnae back against your head.
Listening very closely, U will hear a tiny difference in each case.
By the way, my MS thesis was on General Systems Theory & Cybernetics applied to Human Auditory System

Re: Psychoacoustic Effects of High Freqencies

Reply #22 –
This is 99.95% likely to be room reflections. At 11kHz you will hear level differences due to HRTF's, but it's not likely to completely wipe out sensation at any reasonable level.
-----
J. D. (jj) Johnston
 

Re: Psychoacoustic Effects of High Freqencies

Reply #23 –
Pretty sure about the reflections. Other possibilities is the distance of the speakers. A waveform has a certain length. If one speaker is 1/2 the wavelength further away from you, the can cancel each other out, but reflections are a more common way of cancellation.

If you direct your speakers in another angle the cancellations probably occur at different places.

PS. Are your speakers connected in the right phase ( + and - ) for both speakers? That is also a way to cancel sound, but that affects the audio quality a lot too.

You could play with that also by inverting one channel in an audio editor.

PS. The wavelenght of 11KHz in air is 3.12 centimeters. That means when the speakers have a distance difference to you ear by 1.56 centimeters it gets cancelled out.
Please correct me if I'm wrong!

http://www.webconversiononline.com/wave-length-calculator.aspx?frequency=&scale=hz&medium=air

Foobar 2000 has a plugin to compensate for that. Also nice tool to experiment that, you can move the sweet spot around with that thing.
I don't have the name at this moment. If you like to know that I can look it up for you at home.