Re: [LAU] Rolling off high frequencies when mastering?

On Wednesday 21 April 2010 23:02:19 Arnold Krille wrote:
> Okay, the answers teach me that this is wrong. I didn't yet think about
> this as in-depth as I should have before writing that.

I did some thinking...

Attached is a small python script that generates some sinus data at 0.5, 0.49
and 0.25 the sampling rate, phase shifted pi/2 to the sampling clock. But the
phase shift can be adapted in the first lines.
Then it does fft on these. While the nyquist frequency shows up as amplitude 0
(for phase = pi/2) and 2 (for phase 0), the others remain at amplitude 1 no
matter what the phase is.
Sounds strange, especially when you see the perceived amplitude-modulation for
f=0.49, but in the end its up to the analog filters to create a smaller than
nyquist frequency sinus from the steps returned by the dac...

It is also clear, why f=0.5, phase=0 shows an amplitude of 2: All the
frequencies are endlessly mirrored to the left and right. And at f =
0.5*samplingrate, the mirror and the original are the same.

So sorry for the fuss I tried to spread. Should have done this little exercise
earlier.

Have fun,

Arnold

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