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Old 06 December 2013, 00:29   #101
pandy71
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Join Date: Jun 2010
Location: PL
Posts: 1,546
Quote:
Originally Posted by mc6809e View Post
I know all about reconstruction filters. I asked the question rhetorically so as to illustrate to others that there was an ambiguity in interpreting what the stored waveform really is.
Nope - believe me, your example if antialiasing filter was used and reconstruction filter was used provide always sine - don't ignore Nyquist as it works perfectly.
Use opencalc (or excel) and verify your signal - use spline or cubic line smoothing to simulate lowpass filter.

Quote:
Originally Posted by mc6809e View Post
If the Amiga had been built with a programmable reconstruction filter that could be tuned to the waveform output frequency, then it would be a sample player.
So this is why Amiga filter begin cut energy over 4.5kHz - if you sample signal with maximum DMA OCS speed - signal will be oversampled and antialiasing not present - remember - square wave have unlimited spectrum - lowpass filtering make square no longer square bu bandlimited signal thus Nyquist criteria are meet.

Quote:
Originally Posted by mc6809e View Post
That fact that it only has a couple of gently sloping fixed low pass filters (and even one of these can be turned off) tells us that simple signal reconstruction and playback was not entirely the goal. Synthesis was also the goal.
Just take LTSpice http://www.linear.com/designtools/software/#LTspice and simulate analog circuitry behind Paula output - you will see how integrator and remain part of filter works.
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