If you can hear frequencies up to 20 kHz, you are in the best of aural health, and probably young too. Most of us can't, but some can, and 20 kHz has long since been regarded as the upper limit of human hearing. Of course some animals can hear higher frequencies, dogs and bats come easily to mind, but you can't yet buy a stereo system designed specially to cater to canine ears. I said “yet”.
But in recording, ever higher and higher sampling rates are all the rage. I get people writing to me asking whether the reason their recordings sound terrible is because they don't have 96 kHz sampling.
The plain fact is this: To capture frequencies up to 20 kHz accurately, you need a sampling rate of at least twice that, plus a safety margin. That comes to 44.1 kHz or 48 kHz, depending on whether you're talking about CD or digital audio for video.
Now that is a fact that is measurable on any day of the week, in any high school science lab, anywhere in the world.
But where there's a fact, there's a counter to that fact based on subjective opinion. Anyone into high-end audio in a big way will insist that higher sampling rates are absolutely necessary, and suggest that 96 kHz is merely the beginning. Equipment with a sampling rate of 96 kHz should give an audio response up to at least 40 kHz, and surely that should be sufficient for anyone?
But no. You can buy equipment that samples up to 192 kHz, giving a theoretical audio response of at least 80 kHz. Now we're in the bat cave! (I do note however that Digidesign's highest-specified Pro Tools interface, which samples at 192 Hz, only has a published response up to 20 kHz. What's that all about then?)
I have absolutely nothing against striving for the ultimate in audio. It is human nature to achieve the best, then better it. But the problem is that so many people have somehow gotten hold of the idea that this is the most important thing to worry about in recording.
Not so. If you play recordings sampled at 48 kHz and 96 kHz even to sound engineers and technical experts, they are hard pressed to tell the difference. Mostly they can't. Now try the same tests on a representative sample of the kind of people who might buy your music. I can guarantee that they won't be able to tell the difference – even if you tell them what to look out for.
Now let's turn around to something that makes a real and easily heard difference to a recording – microphone position. Move a microphone a couple of inches, and it's as plain as a billboard right in front of your face what the difference is. Or compare your mixes now with what you did two years ago – there will be a massive difference due to the experience you have gained over that period.
The conclusion is that it is right to be concerned about sound quality, but chasing ever-higher sampling rates isn't the thing most likely to make a difference.