[sdiy] TX81Z, YMxx chips, and aliasing

[Andre Majorel]

On 2018-09-05 13:14 +0100, rburnett at richieburnett.co.uk wrote:

> However, I believe that synths like the DX-7 reduced audible
> aliasing by employing mappings across the keyboard that
> decreased the modulation index of patches progressively for
> higher pitched notes.  Reducing the modulation index in
> Frequency Modulation puts less energy into the higher-order
> sidebands and more energy into the close-in sidebands from the
> FM process, so it results in a signal that has less potential
> to alias badly.

Right, and that was at the discretion of the person designing
the sound. I don't have any experience with the 4-operator chips
used in the TX81Z but I do know that aliasing was easy to run
into with the 6-operator chips used in the DX7. John Chowning
and David Bristow used this fact to estimate the sampling rate
of the DX7 (page 195 in "FM theory and applications").

-- 
André Majorel http://www.teaser.fr/~amajorel/