Vibrato and Portamento effects decrease w/ Just Temperament tuning

[vind]

I'm trying to convert an XM module to the just intonation temperament, using a TUN file that I got from this post. I've got the project converted to the MPTM format and the frequency table imported properly for the instruments. However, what I'm noticing now is that the vibrato and portamento effects in the song have lost their amp, and won't produce the effect that the artist had intended. Is there any way to fix this, when the highest values of the effects won't reproduce the same amplification that even the lowest values otherwise did – preferably without having to manually change every value in the patterns ?

[Saga Musix]

You'll have to set the "finetune steps" for just temperament to 15, it will behave approximately the same as the default tuning then.

and won't produce the effect that the artist had intended.

To begin with, the artist certainly didn't intend to play this song with just temperament.

[vind]

So I just tried that, but it doesn't seem to make any difference. The '12TET' preset also sounds the same, while the 'OMPT IT behaviour' preset is the only one that will play those effects correctly. Any other ideas ??

[Saga Musix]

Random guess - does said XM file use linear frequency slides or not? Non-linear frequency slides are an old relict of the Amiga days and don't map very well into concepts such custom tuning, so tunings always work like linear frequency slides would.

[vind]

Well, I don't think so. The box is not ticked in the song's properties dialogue box. If I open the original XM file and enable this option, the slides will sound like my aforementioned examples (almost flat curves).

[Saga Musix]

Well, that's exactly the problem then - the song does not use the "modern" linear frequency slide system and thus cannot possibly be "emulated" with custom tunings in any sane way. Non-linear frequency slides have the peculiar behaviour of having a different "strength" depending on which octave you are in, i.e. they are less effective in the lower octaves and more effective in the higher ones. You'll have to fix that manually.