KVR Audio

airon · Post by **airon** » Fri Apr 08, 2005 12:14 am

farlukar wrote:total absorption in dB/m for air 20°, r.h. 50%
100 Hz - 2.94·10-4 dB/m
1000 Hz - 4.66·10-3 dB/m
10000 Hz - 1.59·10-1 dB/m
100000 Hz - 3.28 dB/m

Can this be plotted across a logarythmic spectrum ? I wouldn't mind having a bunch of these at the ready.

Could you send in any pointers on the formulas used to calculate this stuff?

nuffink · Post by **nuffink** » Fri Apr 08, 2005 12:34 am

There must also be a small (but real) amplitude dependant non-linearity caused by hysteresis of the air in the chamber.

Shit, if we're devoting 7 pages to a plug that doesn't do anything, may as well get truly pedantic.

jens · Post by **jens** » Fri Apr 08, 2005 12:39 am

nuffink wrote: Shit, if we're devoting 7 pages to a plug that doesn't do anything, may as well get truly pedantic.

Borogove · Post by **Borogove** » Fri Apr 08, 2005 1:24 am

stefancrs wrote:Granted, anechoic rooms does not exist, but that has nothing to do with what I said. Twats!

i

stefancrs

stefancrs · Post by **stefancrs** » Fri Apr 08, 2005 5:17 am

93143 wrote:Air does filter the sound, but it happens by energy absorption (see farlukar's post). Delay... well, air has a characteristic sound speed like any other material, but for a point source and a point receiver, there's only one delay (travel time) and it doesn't cause any filtering.

[Well, not much. There is a frequency dependence to sound speed, but it's small.]

So the wall example I posted. If there's any non-reflective obsticle between the listener and the sound source, won't the sound reach the listener then or does it also travel thru the air other ways than the "direct straight route" ?

Borogove · Post by **Borogove** » Fri Apr 08, 2005 6:55 am

stefancrs wrote:So the wall example I posted. If there's any non-reflective obsticle between the listener and the sound source, won't the sound reach the listener then or does it also travel thru the air other ways than the "direct straight route" ?

Low frequencies refract around the obstacle - higher ones less so. My physics is rusty, but I think the critical bit is the size of the barrier versus the wavelength of the wave. Speed of sound is about 300 meters per second. 20Hz is therefore 16 meters, middle C about 1.25 meters, 6KHz is 5cm. Lowpass filter.

That's why bats and dolphins use high freqs for echolocation, by the way - better resolution. Bats in particular need to be able to pick out flying insects - 5mm resolution requires 60KHz!

(The little bastards use FM, too.)

stefancrs · Post by **stefancrs** » Fri Apr 08, 2005 7:01 am

yeah, but the audio travels an indirect route if it can travel around an obsticle. Won't it travel this route as well even when the obsticle is absent?

airon · Post by **airon** » Fri Apr 08, 2005 7:39 am

This depends on the frequency of the signal. The lower it is, the greater it spreads its energy. THe higher it is, the more directional it is.

You can find what the result of that is in any frequency diagram of microphones.

Stones thrown in a pond or tub can be a good illustration of refraction btw.

I'd like to develop a bunch of forumulas for air absorbtion, based on temperature and humidity, so I can start off quicker on distance EQ'ing in my rerec work.

stefancrs · Post by **stefancrs** » Fri Apr 08, 2005 7:53 am

But, then, an anechoic (ideal version of it) room would still affect the signals in it, since there'd be a certain amount of air in the room. Or does the signal only spread around "stuff" ?

herodotus · Post by **herodotus** » Fri Apr 08, 2005 8:04 am

So why was Smart Electronics picked for this farce???

Just out of curiosity.

farlukar · Post by **farlukar** » Fri Apr 08, 2005 8:56 am

duncanparsons wrote:To reduce the effect of air, why not make an anechoic chamber a vacuum - zero side effects, zero echoes.. perfect!!!

Blimey, all these posts and no one spotted it yet??? I'm a genius - don't know what the rest of you are doing here..

DSP

What you're describing is this one....

whyterabbyt · Post by **whyterabbyt** » Fri Apr 08, 2005 9:03 am

herodotus quoth So why was Smart Electronics picked for this farce???

Just out of curiosity.

You mean the debate? Or the plugin?

The plugin was because Bram picked up on a comment I made in a thread at KVR regarding a set of samples I was intending to sell specifically for artists wanting to preform John Cage's piece 4'33". At the time someone had jumped in and tried to hijack my wonderful business idea. Shortly afterwards Bram jumped in and hijacked my wonderful plugin idea. <sigh>

This time, to save any time before someone rips me off, Ive already emailed Bram directly with my most recent idea...

farlukar · Post by **farlukar** » Fri Apr 08, 2005 9:39 am

airon wrote:
farlukar wrote:total absorption in dB/m for air 20°, r.h. 50%
100 Hz - 2.94·10-4 dB/m
1000 Hz - 4.66·10-3 dB/m
10000 Hz - 1.59·10-1 dB/m
100000 Hz - 3.28 dB/m
Could you send in any pointers on the formulas used to calculate this stuff?

a = acl + arot + avibO + avibN
acr = acl + arot = 1.6·10-10·f²·√((T/T0)·(p0ref/p0))
But you can look it all up in ISO9613-1, if you happen to have that lying around

I can't find anything online, I'll see if I've got anything useful in a pdf.

[edit]
Well well, what have we here...

sangha · Post by **sangha** » Fri Apr 08, 2005 3:04 pm

stefancrs wrote:yeah, but the audio travels an indirect route if it can travel around an obsticle. Won't it travel this route as well even when the obsticle is absent?

If I understand it correctly, the audio isn't travelling indirectly or around anything. It's important to remember that the sound wave is just that...a wave, and so it behaves like a wave. The vibration of one air molecule has an effect on ALL the adjacent molecules, and not just those adjacent molecules that lie directly in front of the vibrating molecule. This is a why a sound wave "expands" as it travels through the air.

(Note: by "expands" I mean that the "size" of the sound wave (the dimensions that contain the air that is vibrating) increases as the distance from the vibrating source increases)

If, by the time the sound wave reaches the obstacle, it has expanded to a size that is greater than the obstacle, then the obstacle can not block ALL of the sound wave. Only the portion that actually "hits" the obstacle is blocked. The portion of the wave the does not hit the obstacle (ie the portion of the wave that is larger than the obstacle) continues (past the sides of the obstacles), and since that is itself a wave, it expands as it passes the obstacle, eventually expanding into the area that lies between the obstacle and intended recipient of the sound wave (ex. mic, listener, oscilloscope, etc)

Borogove · Post by **Borogove** » Fri Apr 08, 2005 3:12 pm

stefancrs wrote:But, then, an anechoic (ideal version of it) room would still affect the signals in it, since there'd be a certain amount of air in the room. Or does the signal only spread around "stuff" ?

I think it only spreads around obstacles, actually, given constant density air, but I am not a physicist.

I don't have a rigorous explanation, but try this thought experiment: Consider a direct path A from sound source to listener, and a line B emitting from the sound source 15 degrees off to one side of A. An impulse from the source implies a high pressure wavefront expanding in all directions.

If an obstacle blocks the wavefront on line A, the wavefront on line B finds a realm of unpressurized air to move into where the A wavefront should have gone, so it spreads into it.

If no obstacle blocks the direct path, the A wavefront "pushes back" against the B wavefront, keeping it in line.

Smart Electronix Anechoic Room Simulator