supersonic beats

I just read a something that might be the first valid reason I've seen for recording and mixing at a higher sampling rate when producing a CD. It would not apply to the kind of thing I do but might, if true, be important for some recordings.

The claim is that some instruments produce enough energy in supersonic frequencies, such as the 30-35kHz range, that two different ones playing together can create beat frequencies humans can hear fairly well. This is an enjoyable aspect of some live music performances.

These instruments might be recorded on separate tracks when recording for a CD. If those higher frequencies are not captured, and maintained until the tracks are mixed, the beats frequency effects can not exist on the CD. Therefore a possible minor, but not insignificant, aspect of live music is missing from the recording.

Is there any reality to this?

Well, it would also mean that you need to keep the phase relations up to those frequencies.

Is there any reality to this?

Yes it happens - but it's rare, directional, very difficult to capture, never mind reproduce and adds no significant listening pleasure for adults (who can't hear supersonic frequencies), who will only wonder what these strange beats are, and think that something's wrong with the recording - and they'd be right, quite frankly...

Reproduced acoustic music at the best of times is no more than a mere shadow of what it's like to be in the room with the instruments - and adding artefacts like that is not the way to improve this situation at all, because it is not one of the significant factors that causes this situation.

No this is about beat frequencies, not the supersonics. 33kHz - 32kHz = 1kHz tone, which is very audible to adults. Does this happen?

No this is about beat frequencies, not the supersonics. 33kHz - 32kHz = 1kHz tone, which is very audible to adults. Does this happen?

Can't you read what I wrote? I didn't put the word 'beats' into the middle of it for nothing...

I believe I understand now. You say that because they can't hear the supersonics, the resultant beats will be confusing. Are these beats from mixing separate tracks at a higher sampling rate different from what naturally occurs, or do these same adults get confused at live performances?

Since I am so often unclear, let me try to make clear that I am not after an argument, I just wanted to know about this aspect of recording. Now we are off on a different aspect, to wit, whether it is better to do a thing or not do it.

If this is something real, then making a stereo recording, or an N track recording for N channel playback, would capture it as a matter of course. Having that happen would seem not to be any disadvantage unless the existence of the beats to begin with is a disadvantage of instruments performing together. Would creating the beats by mixing separate instruments tracks (at the required higher sampling rates) be worse than their occurrence in a live performance?

OT: Sennheiser designed a directional sound delivery system utilizing this principle. http://www.sennheiser.com/sennheiser/icm_eng.nsf/root/09859

Well, maybe the word 'designed' has been misused here. I recall reading somebody's claim that he invented this and discussed it with a Sennheiser engineer to discover a few years later that Sennheiser is making money out of his idea without his knowledge or partcipation.

But I can't locate this information now - and I am not 100% sure if I'm right. I may have mixed two different stories

EDIT:
I found it: his name is Joseph Pompei
http://www.techweb.com/wire/story/TWB20000905S0008
Now he's selling his version of the device as well
http://www.holosonics.com/

Are these beats from mixing separate tracks at a higher sampling rate different from what naturally occurs, or do these same adults get confused at live performances?

You could get intermodualtion beats in a live performance in just the same way that you could if you could actually record them. The difference in a live performance is so great in terms of spatial cues about what's going on that the chances are that you wouldn't notice the effect, or it would seem completely natural - but in a recording, anything like this would just tend to muddy up the midrange, and without the visual/spatial cues it would simply seem like a poorer sound. However you look at this, it's not a good idea to record it - even if you could - which is very dubious, when you consider the directionality/attenuation/absorption issues involved.

If there ARE beats,wouldn't they also impinge upon the mics in a similar way (though not the SAME way, which I guess is part of the problem)?  If this is a natural acoustic phenomenon, I don't see how you could avoid it.

Having said that, I can't remember expreriencing this.

If there ARE beats,wouldn't they also impinge upon the mics in a similar way (though not the SAME way, which I guess is part of the problem)?  If this is a natural acoustic phenomenon, I don't see how you could avoid it.

Being a natural acoustic phenomenon, it obeys natural acoustic laws. The higher the frequency of radiation is, the more it will be attenuated simply by air. It is also very easy for just about anything that this radiation comes into contact with to absorb it quite significantly - it really doesn't travel far at all. In order for it to interact with another instrument, the instrument would have to be close enough, and radiating a dissimilar frequency in the same direction for any intermodulation to develop at all. In an orchestra, this simply doesn't happen to any degree. And if it did, it would be completely swamped by the fundamental tone from a lot of other instruments.

Having said that, I can't remember expreriencing this.

And now you know why!

Look, I'm not saying that it can't happen - if you sit in the middle of an orchestra, you will get to hear a lot of unsavoury sounds, because in any section, the balance of the whole thing is miles out, and you will hear clothes rustling, breathing, etc. The vast majority of it doesn't get much further than where it is occuring - the instrument sound blends with the rest of the orchestral sound to make an overall sound that is sometimes pleasing to the ear - depending on the music being played as much as anything, and the breathing, etc is at a much lower level and swamped by the music. All of these other sounds you are simply not supposed to hear, and by and large you don't; you only hear them locally because of the different relative positions of your ear to the particular source of extraneous sound. They cannot possibly aid your enjoyment of the music, because they will simply be a distraction within the sound... which is why we are better off without them.