Psycho acoustics

[deshead]

Then big boy how is it that dogs can perceive sound above our hearing range. That is a limited definition.

Ya, it's limited, but apropos to this thread. My intent was to back up your point. By the defintion given (which is the first one for "sound" in The American Heritage dictionary), sound isn't really a thing until we perceive it, so it doesn't make sense to separate the physics from the psycho-acoustic manifestation of the physics.

Dogs might use a different definition of sound, but the underlying point remains the same.

And what about breaking the sound barrier. How does that translate to 20 cycles to 20000 cycles. Huh? Huh?

Heh, you know as well as I do.

A tree doesn't need to be heard to be capable of being heard.

Ya, but whether or not it makes a sound is a matter of semantics. If you remove from the defintion of sound the requirement that the vibrations register on a hearing organ, then we're having a different conversation.

It always sounds so freaking smug.

[insert joke about definition of "sounds"]

Everybody loves a pedant!

[Adam!]

A tree doesn't need to be heard to be capable of being heard.

Ya, but whether or not it makes a sound is a matter of semantics. If you remove from the defintion [sic] of sound the requirement that the vibrations register on a hearing organ, then we're having a different conversation.

I really really don't want to prolong this argument, but I also really really want to be clear. You'll notice in your own definition (which I adopted in an effort to avoid "having a different conversation") that "vibrations must register on a hearing organ" is not a requirement of sound. To be sound the vibrations just need enough force and the proper frequencies to be capable of being heard, as opposed to actually being heard. Kind of like an atomic bomb can be capable of levelling a city without having to actually level a city.

I may have misunderstood you, in which case I apologize if this was already obvious.


PS: I'm not normally a cold unfeeling logic-bot.

[deshead]

I may have misunderstood you, in which case I apologize if this was already obvious.

Heh no, it was my fault. I totally glossed over the word "capable", which (as you note) changes the meaning completely. I was going to paste the definition from The Site Which Shall Not Be Named ("Sound is vibration, as perceived by the sense of hearing"), but thought the better of it, and now realize it doesn't actually matter.

So, uh, anyone got any good stories about the mel scale or equivalent rectangular bandwidth?

[Me$$iah]

So, uh, anyone got any good stories about the mel scale or equivalent rectangular bandwidth?

Where else could you find such a bizarre question?

[Mostess]

although we assumedly can't hear below 20 Hz, we can feel frequencies through bone induction and so forth.

The auditory system doesn't respond below about 20Hz. So you can't "hear" below 20Hz. Which doesn't mean you can't be aware of air-pressure changes slower than 20Hz, it just isn't "sound."

I'm having a hard time understanding what you are disputing here. I never said that we could hear below 20 Hz.

Your "assumedly" threw me off, like you were implying that 20Hz hearing floor was just incorrect conventional wisdom. Otherwise, we agree entirely.

Air pressure changes and the perception of these changes are completely inter-related with the physiological properties of the auditory canal. Without the ability to study ways of understanding the human condition in it's perception of sound as it relates to space and the perceived notion of where or what that is, we would never understand psycho-acoustics. Which when you think about is all about physics of sound.
(...)
but if you think that physics of sound and psycho-acoustics are two different things then that would be like saying I'm not related to my grandfather.

I wasn't clear. You're right that sound is a singular phenomenon. And I'm sure you are related to your grandfather (although it's entirely possible that you're not).

My poorly-made point was that psychoacoustics is a field of psychology and acoustics is a field of physics. They are different fields with different perspectives, goals, attitudes, and jargon. And that in my opinion, studying the physics is more useful to the amateur home recording artist.

Of course there are interesting non-linearities about the auditory system that fall outside the realm of physical acoustics. The frequency masking/critical bands phenomenon is one. Fletcher-Munson curve is another. The temporal masking that deshead mentioned is interesting and maybe useful, too.

But you use your ears to record/mix/master so the stuff you hear is already filtered through those non-linearities. If you've set the faders and EQs so it sounds good, you've accounted for the F-M curve and frequency masking problems. Knowing about those issues might help you decide what to try first when you're EQing, but that seems like a lot of work for a little payoff.

[Mostess]

I'm thinking too hard about this. But I just thought of another interesting psychoacoustics thing---one you could actually play with musically.

One way of localizing sounds is the time difference between the ears: a sound to your left reaches your left ear first. Of course there are lots of other cues (the sound to your right ear will be a different volume and timbre because your head is in the way, the little grooves and knobbies on your outer ear create very quick echos that differ depending on the location of the sound, etc.), but if those cues aren't there, your brain will use inter-aural time difference.

Play a fairly low Hz sine-wave over headphones with a certain inter-aural phase difference and you can hear it coming from off-center, even though the amplitude/timbre/frequency is the same to both ears. Changing the phase difference will change the location. If you do the math, you can find frequency/phase difference combinations that are ambiguous---you can mentally switch your brain's interpretation of the location of the sound to one of several possible locations.

If you're really clever, I bet you can find combinations of tones and phase differences that maintain the ambiguity. But your brain is pretty good at eliminating impossible configurations, so it would be really tricky.

And if you really want to create the illusion of location, inter-aural amplitude differences are much less subtle. Hence the pan.

But it's something.

[tonetripper]

Your "assumedly" threw me off, like you were implying that 20Hz hearing floor was just incorrect conventional wisdom. Otherwise, we agree entirely.

I guess I was trying to be inciteful to the scientific and songfight community at large. Sorry it wasn't clear. I think sometimes as humans we rely too heavily on the givens and sometimes don't try to stretch outside of the box. In my world, science sometimes is given too much latitude based on a variety of theses (that are proven extensively ofcourse), when it's proven time and time again that these same scientific proofs can still be proven wrong through some anomolous event that shakes the foundation of the community at large. I still believe that we feel frequencies outside our hearing range and that psycho-acoustically there is some sort of connection physically or emotionally that could be pushed outside (and I'll be careful here) the scientific linear thinking that is imposed on us in regards to sensation and the translation of those sensations.

That was a sweeping generalization ofcourse and more flake than fact. I guess what I'm asking is, "do we in fact translate frequency primarily from the auditory canal or are there other ways of translating frequency that could be construed as "heard"?", although that would not be the best word considering it's connection to the ear? I just like to stir it up a bit even in the wake of overwhelming conclusive scientific proof.

But you use your ears to record/mix/master so the stuff you hear is already filtered through those non-linearities. If you've set the faders and EQs so it sounds good, you've accounted for the F-M curve and frequency masking problems. Knowing about those issues might help you decide what to try first when you're EQing, but that seems like a lot of work for a little payoff.

We agree on most things in this conversation, but this isn't one of those things. Understanding the Fletcher-Munson curve is one of the most utilizable concepts that I employ whenever I am either working as a professional or doing my amateur music work at home. To listen and understand the phenomenom that occurs with the ears at various decibel levels is paramount in understanding why your tune sounds really good loud but no good low or vice-versa. I constantly check final mixes using various levels to find out how the bottom and top-ends translate to my ears. It's one of the best things I ever learned in school besides the physics of sound and the physiology of the ear. And for the record it's not that much work. In fact it's very easy to understand. I paid for the education, but that's not to say that the net has not created a bounty of resources for one to investigate so as to cause them to understand making better mixes. That's like saying that music theory only stints musical creativity. It's all part of the same pool of understanding.

Fletcher-Muson Curve

Notice how we hear the mid range between 850 Hz to 5 KHz the same almost across all the level changes. This is because primarily we hear voices in this range best (average frequency range of voices is approximately 850 Hz to 4.5 KHz). As we get louder in volume the line flattens. Also notice that if you've ever fiddled with a graphic EQ at home on a stereo blasting the tunes that you may use a "disco smile". Cutting the mids and boosting the highs and lows. The F-M curve is completely responsible for me understanding that concept.

[Mostess]

I guess what I'm asking is, "do we in fact translate frequency primarily from the auditory canal or are there other ways of translating frequency that could be construed as "heard"?", although that would not be the best word considering it's connection to the ear? I just like to stir it up a bit even in the wake of overwhelming conclusive scientific proof. :twisted:

So my hunch was right. I just took your bait. Silly me.

But you use your ears to record/mix/master so the stuff you hear is already filtered through those non-linearities.(...)

(...)I constantly check final mixes using various levels to find out how the bottom and top-ends translate to my ears.

Funny you compare this discussion to the music theory one (though I'm not saying understanding stints anything), because I like to take the other side in that one. The question seems to be does an academic or technical understanding of how you do something help you do it better? And the answer is probably yes, though it's really an empirical question. It's just a question of how much it helps and at what cost.

No doubt you're a professional sound engineer, so you want to know what your dealing with. But in your example, you're using your ears to test the theory and decide on the best mix. So someone without the theory can still use their ears. Most of us (it seems) do it quite well.

We don't really understand much of what our brain does to translate physics into perception. Understanding how your retina responds to arrays of spatial frequencies, divides that information into seperate pathways which get recombined in several specialized brain areas, etc. is fun and perhaps quite useful. But you can see just fine without it.

That said, I do think it's a good idea to get an audiogram and can see how your frequency sensitivity function differs from the norm; that's some academic knowledge that changes how you mix things.

[roymond]

The auditory system doesn't respond below about 20Hz. So you can't "hear" below 20Hz. Which doesn't mean you can't be aware of air-pressure changes slower than 20Hz, it just isn't "sound."

I'm having a hard time understanding what you are disputing here. I never said that we could hear below 20 Hz.

Your "assumedly" threw me off, like you were implying that 20Hz hearing floor was just incorrect conventional wisdom. Otherwise, we agree entirely.

I'm afraid of getting caught up in this, but would point out that although we can't hear below 20 Hz, we can hear the effects that sub-20 Hz sounds have on other sounds that are in our range, through sympothetic resonance, etc. Plus there's the whole "the dance floor is throbbing" thing.

Play a fairly low Hz sine-wave over headphones with a certain inter-aural phase difference and you can hear it coming from off-center, even though the amplitude/timbre/frequency is the same to both ears. Changing the phase difference will change the location. If you do the math, you can find frequency/phase difference combinations that are ambiguous---you can mentally switch your brain's interpretation of the location of the sound to one of several possible locations.

OMG! Last week I entered the apartment of a neighbor who had just moved out. Their carbon-dioxide detector was blasting that shrill, non-directional alarm, since he had unplugged it and the back-up 9 volt battery was almost dead. I spent 45 minutes trying to find the damn thing - I couldn't even figure out what room it was in. THIS WAS AN ALMOST COMPLETELY EMPTY APARTMENT!!! I ended up walking around and in and out of rooms carrying each of the five paper bags of left-overs that he had piled up, listening for subtle clues as to whether this thing was in them. Even when I held it in my hands I couldn't tell that the noise was coming from the device. When I pulled the battery out it didn't stop right away because there's a capacitor, so it took almost 10 seconds to stop. I was just about to go out of my freakin mind. But had a beer instead.

Is this off topic?

[deshead]

beer ... Is this off topic?

Never.

This might be though.