Comment by femto
14 years ago
Playing Devil's Advocate...
The statement that frequencies above 20kHz don't matter rests upon the assumption that the ear is linear. If the ear is not linear (I don't know whether it is not not) then frequencies above 20kHz will matter, as the ear will be able to mix higher frequencies down to less than 20kHz. For example, if we have frequencies of 56kHz and 59kHz, the ear MIGHT be able to discern a difference frequency of 3kHz. No doubt this effect could be reproduced by signal with a sampling rate of 44.1KHz, but only if the analogue systems, before the sampling stage, reproduce any non-linearity in the human ear.
Incidentally, you can get speakers that create a localised beam of sound, that the person sitting next to you cannot hear. They work by transmitting frequencies above the audible range. These high frequencies can be beamformed by a relaitively small speaker array, so the sound is localised. They then rely on the non-linearity of the ear (or maybe the air around the ear?) to mix the ultrasonic frequencies down to audible frequencies. I guess there must be non-linearity in the human auditory system!
On the subject of 24-bits my understanding is that 16-bits is adequate, provided the levels (scaling) are set correctly in the recording. What 24-bits delivers is the ability to do a crappy job of the mixing, and still end up with the full dynamic range of the human ear. 24-bits is probably a temporary solution though, as manufacturers will engage in the usual Loudness War [1], and push the signal to the top of the dynamic range. Before long 24-bit audio will be equivalent to 16-bits (since the 8 least significant bits will be unused) and the next big thing will be 32-bit audio.
Having said all that, I'd guess that the speakers will be the limiting factor in most sound systems, not the recording format.
Nonlinearity of the ear is thought to be the explanation for sum and difference tones, which most certainly exist: https://en.wikipedia.org/wiki/Combination_tone.
> Having said all that, I'd guess that the speakers will be the limiting factor in most sound systems, not the recording format.
Yes. And DACs, which normally have filters too.
Yes, though I tend to think of the reconstruction filters as being part of the recording format.
Here's an interesting article:
In 1975, the Canadian Broadcasting Corporation was using a head shaped microphone, which was presumably an attempt to reproduce the non-linearity of the ear. It would be interesting to do such experiments with digital sampling.
Thinking about it, if every person has a different non-linear response, in theory the only way to reproduce sound beyond a certain threshold of fidelity would be to reproduce the ultrasonic components, so each person would hear their own non-linearity. (That would be beyond what I can hear or care about, but it would be fun to play with. Beyond a certain level we also get to the point where we need to ask what it means to hear a sound.)
I disagree -- in most sound systems, the room is generally the most limiting factor.
Pardon the reductio ad absurdum, but would you prefer to listen to $1,000 speakers in a dry, padded listening room, or to $100,000 speakers in a tile bathroom? Obviously the room matters; I think most people underestimate by how much.
Probably. I should have left it at "it's not the recording format" and not nominated a limiting factor.
I'd take the bathroom, given that my singing voice sounds less worse there! :-)