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Best anti-aliasing filter?

DSP related issues, mathematics, processing and techniques

Best anti-aliasing filter?

Postby Spogg » Mon Sep 14, 2015 9:00 am

Hi you clever ones!

I fear this is going to be seen as a naive question but since there has been a lot of talk about filters it's at least a simple one I think...

Does anyone have the very best filter module to efficiently provide a brick-wall filter to kill aliasing dead? Something that removes all frequencies above say 20kHz coming out of e.g. a naive sawtooth oscillator or simple pwm source and doesn't cause any unwanted side effects like audible ringing or heavy CPU use.
I do know it must be low-pass in funcion of course but I would like to see what would be thought of as the "best" way to do it.

Cheers

Spogg
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Re: Best anti-aliasing filter?

Postby martinvicanek » Mon Sep 14, 2015 8:05 pm

Mr, Spogg, don't know if I am clever but so much I know: no brickwall filter whatsoever will remove aliasing once it is there. You have to prevent it from occurring in the first place.
Very steep filters will always tend to ring, that's the tradeoff.
MyCo has some very efficient decimation filters in his oversampling toolkit which he posted here some time ago.
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Re: Best anti-aliasing filter?

Postby Spogg » Tue Sep 15, 2015 10:02 am

Please forgive and be patient with an ageing Vulcan whose logic is not what it was.

I can now see that, having read about polyBLEP theory, that the limitation of frequencies at and above Nyquist must be done during the wave generation process and not after! So the bandwidth must be limited before the wave gets out of the DSP box and into the schematic.

My erroneous assumption was that since we must band limit (low pass) a signal before we sample it that we could do the same after it appears in digital form. This idea led to the thought that the polyBLEP process could exist outside the oscillator in a separate module and thus be useable for any waveform or signal.

Oh well... Kling akhlami buhfik

Cheers

Spogg
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