Sample-based oscillators have pitch instability with notes sustained for long

[rktic]

In both versions—native and non-native—sustaining notes using type 4/GM.dll samples drop pitch after a moment. Which gets really random with chords :)

To me, the GM samples are very interesting as wavetables. Offering a lot of potential for more effective/smaller patches. Which I'll definitely want to revisit in future projects. Would be great it the issue was fixed in future versions!

Steps to reproduce:

1. Load Sointu Native
2. Set oscillator type to 4
3. Set sample 1
4. Play and sustain any note

[vsariola]

This is a difficult to fix but I'll see what can I do. The reason is that oscillator phase is 32 bit floats and those pitch shifts are from rounding errors when adding a small value every sample to the phase.