Sine and square waves percieved pitch, why?

[KBK]

When you have a square wave at low frequency, there is time for the system (ear brain-air) to re-stabilize at the either positive DC point or the negative one. The 'change' in the signal, at this point, becomes the 'crossover' component, the 'zero crossover' point. Thus, for a given low frequency square wave, the single cycle, or frequency, has multiple points where the ear-brain can hear it as a frequency, or 'transient change' point. Whereas, a sine wave only has the two. That likely would be the more plausible answer, on analysis of the situation. As you increase the frequency of the square wave, this phenomena of the air re-stabilizing, masking effects, etc..all cease to have as large an influence, and you would slowly change over to a singular frequency recognition with the ear-brain system of signal recognition, on that given square wave 'cycle'.(as it increases in frequency of cycles) It might be more correct to say that the air re-stabilization effect is still there, obviously, but we have passed through the frequency and pressure area where the eair-brain's air pressure sensitivity (as a system) have altered in their understanding on how they interpret this phenomena.

As for the sound of a signal being audible, even if the wiring of a speaker is reveresed, some folks, like me, and many, many audiophiles, have learned to recognise 'reverse phase' signals very easily,and find them to be disturbing. It almost feels like the brain and ear are turned 'inside out'. I would liken it to seeing a mirror image, as in when you look at a mirror.

Make sense?

[phn]

I can only second KBK. Before designing audio we should know what we can hear. Thankfully there are tons of academic books on the human senses out there. But my favourite by far is Diane Ackerman's A Natural History of the Senses. There's no tech talk. Just a very well written, easily read and entertaining book. You will not find this a chore. The engineers here may prefer books with figures and graphs and stuff. But if you visit any library you should find enough of those to last you a couple of years reading.

[Enzo]

All the preceding discussion has just assumed this is an artifact of the human ear. What you havevn't done is considered the way the sound was delivered to the test subjects. What speaker did you use? What was the listening environment? We can probably assume the amplifier had response well below the 100Hz, but we don't know how well it responds.

Speakers that don't have low end response can be fooled. We often bump a bit at maybe 250 to fool the ear into thinking there was more bottom than there is.

Your speaker may have some resonances that interfere. If it is a multidriver speaker system, then there may be interaction between the drivers or in the crossover. The sine will be all fundamental and will come out hte woofer, but the square wave has high freq components that will come out the tweeter or midrange, and there may be phase differnces between them that affect the perceived sound. Sum and difference signals would then confuse the ear.

And the response of most speakers is not linear. The impedance of the speaker varies with freq as well.

Room acoustics matter, resonances and standing waves can alter perceptions. Reverberations or sound reflections may be frequency dependent. Was this sound presented through a stereo setup? Or one speaker? And what about the room around it. Try your experiment in another setting and with different equipment before drawing firm conclusions.

If you want to test the ear in this experiment, should you not do it in an anechoic chamber?

ANother thing is level. SPL can alter the perceived freq in some circumstances. Look up the FLetcher Munson curves. At lower levels your ear has a reduced response range, so as you get louder, yuo can hear deeper tones. This might be involved.

You might pick up the test sound with a calibrated microphone and analyze for any phase aberations or intermodulation artifacts.

It is an interesting experiment, but don't jump to conclusions.

[Enzo]

What I meant by level considerations was that if the sine and square signals were not absolutely matched in level, it will hit the ear different. and the 200Hz transition migh tbe where the FM curves were crossed in your tests.

[johnnyx]

I think it's to do with time.
Another experiment is to gate a tone on and off. Vary the duration of the tone with the gate, gradually reducing it.
You get a tone, a short tone, a very short tone, a very very short tone, a click.
At what duration does the tone become a click?

[baggystevo82]

Hello, was done with a
PP KT88 amp (diyhifisupply ella)
B&W 309
Creative labs external sound card (MP3+ I think)
Stereo setup

Good point, i should at least have tried it with headphones, something to do later...

cheers,
Steve

[jeff mai]

Originally posted by dnsey
It therefore seems likely that the first harmonic of the sq wave is more easily perceived than the fundemental frequency.

The above is the answer, but no one seems to have understood. There is no need to refer to diodes or transient perception to explain this.

The graph is only showing that the ear is increasingly less sensitive to frequencies below 200Hz. A square wave is a sine wave plus a series of harmonics (a perfect square wave would have an inifinite series.) Below 200Hz the ear perceives the first harmonic present in the square wave as being louder than the fundamental of the square wave. Therefore, where the fundamental of the sine wave of frequency "f" is below 200Hz, the required square wave frequency that is an audible match will be "f/2". Plain and simple.

[KBK]

Which is why I said inductively filter the square wave. To remove the harmonics, which give those cues you speak of. To get to a more of a single cause analysis situation. Ringing of the wave at transition, settling, etc. Get it out,and see again what the results are, then you will know if you are paying attention to the ringing or the transition.

Only problem being, is the driver and amplifier will do it too. The diode analysis is solid and well known, regardless. It's pertinence here is the question.

[Enzo]

If you filter the harmonics out of a square wave, does it not cease to be a square wave? And at that point we are no longer doing the assigned experiment.

[baggystevo82]

True, but my amp ought to be capable of making a pretty accurate square wave at only 200Hz.... Maybe at 10k there would be significant rounding
Steve