[Sesse__]

Sure, you can implement the pre-sampling filter as a multistage filter, of which some of the stages are digital, if you wish. (I don't know where you get “rejecting from 22050 and up” from, though. For the pre-sample filter, you should reject from 20000 and up, and for the reconstruction filter, you should either reject from 24100 and up or 28000 and up, depending on whether you ended up sampling in 44.1 or 48.) But I don't think your argument makes much sense; if you're already in a domain where you have enough resources to sample at 384 kHz and run a 384-tap FIR filter over it, then surely you're high-end enough that you can't say “nah, who cares about the most common sample rate out there”.

[mlyle]

When sampling:

You should pass all below 20KHz, as flat as possible. You definitely should stop 24.1KHz and up. How bad 22.05KHz to 24.1KHz is, is debatable.

> then surely you're high-end enough that you can't say “nah, who cares about the most common sample rate out there”.

I didn't say "don't support 44.1KHz" -- I'm saying there's good reasons to prefer 48KHz.

All being equal (same number of filter taps, etc)-- just a slightly higher sample rate offers a lot more performance because you can get a bit more frequency response and a lot flatter passband.

[alfiedotwtf]

The Moog Minimoog filter goes beyond 20Khz. So even if you gently roll off at 20Khz, you’re going to miss overtones etc.

[Sesse__]

You can't hear ultrasound. For audio, the only question about 20+ kHz frequencies is how to get rid of them in the cheapest+best way.

[alfiedotwtf]

But they still interact with frequencies lower than 20khz right?

Think about it like this - I have a single steady saw wave at 10khz. If I started playing waves above 20khz, would I be able to detect any disturbance in that 10khz wave?

[Sesse__]

> But they still interact with frequencies lower than 20khz right?

No. Different frequencies don't generally “interact”, that's much of the point of frequency analysis.

> Think about it like this - I have a single steady saw wave at 10khz. If I started playing waves above 20khz, would I be able to detect any disturbance in that 10khz wave?

No.

If you have a green laser and put its beam under an ultraviolet light source, does the green laser change? It does not. It's the same thing.

Of course, if your amplifier is badly nonlinear-and-non-time-invariant in a very weird way, it _might_. But usually, even nonlinearities go the other way (creates overtones upwards in frequency, not undertones).

[alfiedotwtf]

Oh.

Hmm… then what causes the obvious beating you hear when you have two saw waves close in frequency but not exact.

I guess when the anti-nodes match its silence and so it’s obvious to your ear, but nothing magical is happening to the signals themselves. Interesting, thanks for answering!

In that case filtering out everything over 20khz makes total sense!