Psycho acoustics

[Bell Green]

Anyone know anything about psycho acoustics? I was reading lots of articles online last night about reverberation and it's one of the ways that we perceive space or distance. That got me onto compression ie modifying the perceived loudness. Which then got me onto how the human ear perceives sound. That's called psycho acoustics if I'm not mistaken. So I thought what do I know about that? The Fletcher-Munson contour curves and that's about it. So afore I starts googling around maybe some of you chaps and chapesses already have a handle on this subject.

Better have another glass of wine, perhaps that will make my mix sound a bit better.

[Kamakura]

Better have another glass of wine, perhaps that will make my mix sound a bit better.

Try the Fletcher-Munson '92 Cabernet. Excellent for most mixes, though not Reggae.

Psycho acoustics is a facinating subject about which I know not a lot, though I would like to try a mix or two in 5.1 surround at some point in the dim future.

[Adam!]

I learned a fair bit about both how the ear perceives sound and the psychoacoustics involved in mp3 compression for school. Any specific questions?

[Bell Green]

Specifics, blimey. Um. Oh yeah.
Just to continue from my knowledge so far. With the Fletcher-Munson curves, they are averages, so that would mean that there are people that don't perceive frequencies in that way, but how many. That would be interesting to know.

I read somewhere, online I think, that the resolution of the ear is 2hz, but it is possible to go beyond that using beat frequencies. I am used to listening to beat frequencies when I'm tuning the guitar, but perhaps there are ways to use this creatively in music. For example, to create notes that are not heard. Any ideas about beat frequencies and how one could use them creatively?

Sorry if it's not too clear, but as I said, I have limited knowledge in this area.

[jb]

*starts pool on how long before fluffy responds to this thread*

[jack]

i was watching a recent episode of "Mythbusters" and they did a segment on proving or disproving "the brown note theory". they had a guy in diapers standing in front of these walls of speaker cabinets.

it didn't work. (myth)

[tonetripper]

All I know is that one thing that blew me away in school learning about recording is that although we assumedly can't hear below 20 Hz, we can feel frequencies through bone induction and so forth. This has been proved by sending 11 Hz to 13 Hz out of a speaker and realizing that the sphincter muscles in your ass become relaxed enough to make you shit. This ofcourse is achieved through a high decibel level of said frequencies.

The Fletcher-Munson curve is great for understanding how the human ear perceives frequencies at different decibel levels. Great for understanding the mix. Optimally we hear best across the board at about 70 db spl or so. The lower we get in level the less we perceive tops and bottoms and as we rise in level these frequencies become clearer. The threshold of pain is 130 db and the speed of sound is 1128 ft/s which can open up a whole world of understanding in acoustics and resonant frequencies in rooms. The formula for figuring out a resonant frequency in a room is: Speed of sound/2/dimension=resonant frequency. Therefore if the width is 10 feet square, then the resonant frequence will be 56.4 Hz and every frequency multiple of that will ring as well but these frequencies are usually only problematic below 300 Hz. Sympathetic frequencies will ring in addition, but the base will be the most prominent.

There is a lot more that can be learned from Psycho-acoustics. Everything from general room acoustics to finding out why a frequency is particularly prominent, to making better mixes, to why all of a sudden you want to take a shit so bad. Welcome to the wonderful world of the physics of sound.

[jack]

This has been proved by sending 11 Hz to 13 Hz out of a speaker and realizing that the sphincter muscles in your ass become relaxed enough to make you shit. This ofcourse is achieved through a high decibel level of said frequencies.

as i previously stated, this is more bull shit than real shit.

the brown note debunked

[Mostess]

Anyone know anything about psycho acoustics?

Yes. Though it's not my strong psychology suit.

Not very helpful to my songwriting or recording. Barely helpful to my mixing. Maybe if I were a mastering master, I'd find some useful.

Probably the most useful topic in psychoacoustics for mixing "critical bands." Though it's really not that useful (to me). But here's brain dump of what I know off the top of my head (feel free to embarass me with corrections, but the spirit of it is certainly right):

When your eardrum vibrates, it sets up a vibration pattern on the basilar membrane. The basilar membrane is skinny and thin where it attaches to the eardrum and gets fatter and wider towards the other end. So each eardrum-vibration frequency makes a certain part of the basilar membrane vibrate---low Hz make parts at the far end vibrate, high Hz make parts at the near end vibrate. Hair cells on the basilar membrane get flopped around when their part of the membrane vibrates, and that sends neural signals to the brain. Different neurons for different frequencies, more activity for higher amplitudes.

There's a bit of a problem that when one frequency is present, causing the corresponding part of the membrane to vibrate, neighboring areas get vibrated a bit, too. Your brain has a way of finding the frequency causing the most activity, and actually sending signals back to hair cells on adjacent parts of the membrane, causing those hairs to stiffen and decrease the vibration there. So, you actually become a little deaf to frequencies immediately above and below strong ones.

This means that if I play a weak tone at 400Hz, you can hear it. But if I play a strong tone at 392Hz and the same weak tone at 400Hz, you won't hear the 400Hz one as well. And if I play a strong tone and 300Hz and the same weak tone at 400Hz, you'll hear the 400Hz just fine.

The frequency range of the "deafening" is called a critical band. MP3 files get a lot of file compression by eliminating weak frequency information within the critical bands around strong frequencies.

[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."

There is a lot more that can be learned from Psycho-acoustics.... Welcome to the wonderful world of the physics of sound.

Two different things.

I think you'll find that room acoustics and "that darned frequency" prominance problems are more physics than psychoacoustics. Psychoacoustics deals with the relationship between air pressure changes around your head and the psychological, subjective experience of "sound." Room acoustics change properties of the air pressure changes produced immediately by some noise-maker, and your ear/inner-ear/brain are remarkably good at parsing sounds to make inferences about room size, wall material, location and velocity of the noise-maker, etc. Basically, your ear already understands the physics of sound and psychoacoustics is about figuring out how it translates air pressure changes into a perception of physical space.

So if you want your recording to fool a listener into thinking that your drum is in a spherical 20' diameter concrete room, you should study the sound absorbtion properties of concrete and the resonant frequencies at certain locations inside a 20' diameter sphere. Knowing internal wiring of the auditory system won't help you much.

[Hoblit]

Lets just build the weapons...

[Bell Green]

The formula for figuring out a resonant frequency in a room is: Speed of sound/2/dimension=resonant frequency. Therefore if the width is 10 feet square, then the resonant frequence will be 56.4 Hz and every frequency multiple of that will ring as well but these frequencies are usually only problematic below 300 Hz. Sympathetic frequencies will ring in addition, but the base will be the most prominent.

Wow, I think I stumbled across this without knowing it many years ago. When I'm in the bath I sing notes until I can find one that can make the room resonate, like the whole room is singing with me. So there is a way to figure that out using a formula. Cool.

[Bell Green]

So if you want your recording to fool a listener into thinking that your drum is in a spherical 20' diameter concrete room, you should study the sound absorbtion properties of concrete and the resonant frequencies at certain locations inside a 20' diameter sphere. Knowing internal wiring of the auditory system won't help you much.

I suppose what I was looking for were ways to create special effects in music. Equivalent to sumliminal flash frames in movies, which have been banned I think or strobe effects. Those kinds of things. Not really musical I guess, more in the region of gimmicks but fun for a while.

I checked out this thing called Binaural Beats. It's about changing your brainwave patterns using beat frequencies. We can't hear 4hz but we can fool the brain into thinking that it is hearing 4hz by putting different tones in each ear so that the beat frequency is 4hz. I created a sine wave synth patch to do just this and called it theta wave. I left it playing for a while while i was surfing, but didn't really notice anything, ie any changes in mental/emotional state.

[jute gyte]

I left it playing for a while while i was surfing, but didn't really notice anything, ie any changes in mental/emotional state.

were you using headphones? they're vital.

[Bell Green]

Absolutely. I tried it again last night, but I did get into this sort of eerie/spooky state like after watching a horror movie or listening to ghost stories around the camp fire. Then I took them off.

[deshead]

Along with the frequency masking that Mostess described, our brains also do "temporal" masking, where a sound masks similar sounds that arrive at our ears within 20ms. The brain fuses the two sounds, but uses the time difference between them to determine directionality (which is how we hear directionality in our everyday lives: Sounds originatinating to the left arrive at our left ear first.)

This is known as the "precedence effect", and also the "Haas effect". You can use it to in your mixes to place sounds in the stereo or surround field much more accurately than using a pan pot.

[Caravan Ray]

i was watching a recent episode of "Mythbusters" and they did a segment on proving or disproving "the brown note theory". they had a guy in diapers standing in front of these walls of speaker cabinets.

it didn't work. (myth)

I don't care - I'm still gonna keep searching for that brown note every week. Some may argue I hit it regularly.

________________

Possible future Alternate Fight Challenge - Brown Notes Only

[tonetripper]

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. However, I still fundamentally believe that you can feel frequencies outside of the scientifically proven hearing range. Just because we can't perceive it as a frequency doesn't mean that your body can not connect with it. There are endless stories of people picking up RF frequencies and the like, in addition to sound being used to heal and monitor the body. There is a lot that science has not explained in terms of perception of sound as it affects our human condition. Scientist are just now trying to understand how RF pollution is affecting us humans (eg. Cell Phones). I was just making a generalization that the auditory canal is the way we perceive frequency and pitch, but the body has many other levels in relating to frequency. Bone induction is an extension of this thought and is directly related to psycho-acoustics. And for the record "Sound" lives outside of the hearing range. Just because we can't hear it doesn't mean it doesn't exist.

There is a lot more that can be learned from Psycho-acoustics.... Welcome to the wonderful world of the physics of sound.

Two different things.

No they are not. They are completely joined at the hip. The definition of sound is: Sound is when air gets pushed. 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.

My thesis in school was in Control Room Acoustics and my feeling was always that the relationship between the physiological properties of the ear combined with our own personal interpretation of sound are completely intertwined and when you understand these basic concepts that the things that you hear will be able to be put in perspective. Physics of sound is far too vast for you to put a cap on it and it's relationship to psycho-acoustics. For me, physics of sound is at the very core of psycho-acoustics as is the way that we perceived psycho-acoustics in the first place. Without the science it would just be magic.

The Fletcher-Munson curve is also directly related to psycho-acoustics as these curves are the various stages of decibel level that the average human perceives air pressure changes or frequency and is based on being in a completely flat room with no phase or flange issues, and no nodes or anti-nodes. Nodes and anti-nodes are at the very core of acoustics and I would hazard to say that these over or under abundance of frequency dictate acoustical frequency response which in turn can dictate our perception of frequency and it's room acoustics. Understanding the absorption coefficients and reverberant natures of materials won't allow us to think any more clearly about psycho-acoustics any more or less than understanding the general physics of sound.

And for the record I was being flippant when I posted earlier, because the person asking wanted some info and I was informing them of those things (in addition to other things). I'm not going to debate your definition of psycho-acoustics as you are right on the money, 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. Before you can even grapple a concept like psycho-acoustics you need to understand the physics of sound and the properties that affect it.

Knowing internal wiring of the auditory system won't help you much.

I beg to differ. First paper I wrote in recording school before moving onto heavier concepts such as control room acoustics and psycho-acoustics. Understanding the physiology of the ear and why we hear are at the core of psycho-acoustics.

[deshead]

Sound is when air gets pushed.

Even more specifically, sound is "vibrations transmitted through an elastic solid or a liquid or gas, with frequencies in the approximate range of 20 to 20,000 hertz, capable of being detected by human organs of hearing."

A "hearing organ" is integral to the definition. Which is to say: If a tree falls in a forest and no one's around, it categorically does NOT make a sound. </derail>

[tonetripper]

Then big boy how is it that dogs can perceive sound above our hearing range. That is a limited definition. And what about breaking the sound barrier. How does that translate to 20 cycles to 20000 cycles. Huh? Huh?

[Adam!]

Sound is "vibrations transmitted through an elastic solid or a liquid or gas, with frequencies in the approximate range of 20 to 20,000 hertz, capable of being detected by human organs of hearing."

If a tree falls in a forest and no one's around, it categorically does NOT make a sound.

Clever, but wrong. Efficacy does not imply effectuation. A tree doesn't need to be heard to be capable of being heard.

Sorry. I just hate that argument. It always sounds so freaking smug.

[Adam!]

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

They can't. Neither can bats. Most good resources about either mammal will be careful to say something like "Bats can hear ultrasonic waves" or "Dogs can detect frequencies above our normal hearing range". But you're right: an ultrasonic sound is a contradiction in terms.

Everybody loves a pedant!