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Old 14 March 2017, 17:52   #21
Foebane
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Join Date: Sep 2011
Location: Cardiff, UK
Posts: 442
Quote:
Originally Posted by demolition View Post
The low pass filter can be considered a part of the DAC circuit, also known as a reconstruction filter:
https://en.wikipedia.org/wiki/Reconstruction_filter

Mirror images of the frequencies in the audio signal are created around the half of the sampling frequency of the DAC and some kind of low pass filter must be used if you want to remove these, or at least attenuate them.

This theory also applies to the samples being played back which are played at a lower sampling rate than the DAC/Paula itself, thus some kind of sample rate conversion is involved (and nearest neighbor is a very crude way of doing it). The overtones from the sample rate conversion is probably the main reason why you would want a low pass filter, however ideally the filter should be applied separately to each channel with a cut off frequency tracking each sample's sampling frequency, so having just one filter and being able to turn it on and off was probably as good as what could realistically be done.
Doesn't the Creative Sound Blaster (or GUS or any PC sound card) work along similar principles on playing back samples at different sampling rates?

The only problem I have with Amiga audio is that low KHz samples can sound bad when played back at lower frequencies. You get this distortion that is audible at low frequencies and gradually fades out as the frequencies get higher. The bass notes in the first minute of the first tune of Odyssey by Alcatraz is a prime example (listen for the first minute): [ Show youtube player ]

Sometimes I swear I can hear other musical notes in particular samples that I think weren't meant to be there, but I think that's down to the sampling source.

In all, I've always been impressed by Paula, but for someone to come along and say it wasn't as good as it should've been is an insult to Jay Miner and the other Amiga engineers.
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