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Demos Amiga Demoscene Archive Forum / Coding / 14 bit playback

 

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Blueberry
Member
#1 - Posted: 1 Mar 2011 13:04
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Hi!

As we all know, we can emulate 14 bit sample playback by playing one channel at volume 64 and the other channel for the same speaker at volume 1.

Now, one of the problems with this technique is that the Amiga D/A converters are crap - in particular, the actual voltage distance between adjacent sample values is not the same for all values. And these errors are different for different Amigas. This problem can be somewhat amended by calibrating the Amiga, that is, measuring the distance between adjacent sample values in terms of the volume 1 channel, and taking the measured distances into account when playing.

Calibration is a lengthy process, so we cannot expect everybody who wants to watch a demo on their Amiga to go through calibration first. Thus, for demos, we must contend ourselves with the non-calibrated variant.

This leads me to my question: When playing back non-calibrated 14 bit sound, what is the best way to do it? I see several options:
- Using all values of the volume 64 channel and varying the volume 1 channel between 0 and 63 (or perhaps between -32 and 31), i.e. 8 high bits and 6 low bits.
- Using only values divisible by 4 in the volume 64 channel and varying the volume 1 channel between -128 and 127, i.e. 6 high bits and 8 low bits.
- Changing the volume 64 sample value as rarely as possible, trying to encompass long intervals only varying the volume 1 value.
- Something else?

Has anyone performed any experiments as to which strategy sounds best on a real Amiga?
britelite
Member
#2 - Posted: 1 Mar 2011 13:22
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I'm currently using 8 high bits and 6 low bits, as that sounds good enough and clearly better than just 8 bits. And it's fast :)

 

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A.D.A. Amiga Demoscene Archive, Version 3.0