Comment by noonespecial
14 years ago
I was under the impression that two inaudible high frequency tones could interfere with each other to create an audible interference pattern. (I think known as a "beat frequency").
If this is the case, then all of the arguments in the world about the maximum audible single frequency are irrelevant. Imagine music composed entirely of these beat frequencies and performed with a pair of oscillators between 25kHz and 35kHz. Without higher resolution encoding, it would be audible IRL but the recording would be silence.
If the beat frequency is audible, it will be on the recording. Obviously.
That would suppose that the recording device precisely matched the orientation of the listener, and the recording was not created digitally in (multi-track fashion for example). There would have to be air space in order for the interference pattern to set up in.
So you'd be right if your mics were head spaced and in the venue. But you'd still have secondary data, with the original lost.
> But you'd still have secondary data, with the original lost.
By that standard, the original is always lost unless you have a completely holographic recording. 192kHz doesn't help with that problem at all.
Alas, they don't— you can easily demonstrate this for yourself. Startup an audio editor and generate tones at 25k and 28k (make sure you can't hear them— otherwise you have severe distortion screwing up your test) then play both at once. You will not hear a 3kHz tone.
The tone you get from an acoustic beat is not a real tone— it's a perceptual quark that requires you to be able to hear the tones in the first place.
I tried this in Audacity, with the project set to 96kHz and two tones at 25kHz and 28kHz. I couldn't hear either of the tones individually, but I could hear a tone when played together. This is on Windows 7 with the sound card configured for 24-bit/48kHz. Am I running into resampling artifacts somewhere in the chain?
EDIT: it turns out Audacity won't generate a tone above 20kHz (the UI accepts the value, but when you reopen it the value has been rounded down), so both of my generated tones were actually 20kHz.
I tried this with 19kHz and 20kHz. Couldn't hear any of them on their own, but very clearly together.
EDIT: You can generate higher than 20kHz by increasing the pitch of a tone lower than 20kHz. Upon doing this, I could hear 24kHz and 26kHz together.