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Old 03 December 2013, 00:53   #39
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Join Date: Jun 2012
Location: Duluth, Minnesota (USA)
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Originally Posted by mc6809e View Post
Aliasing of this sort has absolutely nothing to do with Amiga audio hardware in particular. It happens at the moment the original signal is sampled below twice the Nyquist limit without proper filtering and is stored. Before the first byte of the stored sample is output, aliasing has already been introduced into the stored waveform. The Amiga doesn't "resample" this stored waveform. It outputs each and every point of the waveform at a desired rate. No additional aliasing is created.
Yes, definitely. However, my point is that the aliasing noise changes frequency with the frequency of the individual channel. (And since the filter(s) on the output of real Amiga hardware have a fixed cutoff frequency, it may fall entirely within the passband on lower notes.) In the right circumstances, it can even wind up enhancing particular harmonics in the sample. That isn't something unique to the Amiga (it will happen on any digital sound source that uses multiple independent DACs at independent rates for the output channels, such as many '80s sampler keyboards,) but it is something different from what's done to a sound on something like a PC sound card, where everything is resampled to a fixed master sample rate. It's certainly a component of the Amiga sound, even if it's not completely unique to the Amiga.
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