F0 flutter is applied incrementally

[chdh]

The F0 flutter value, calculated with the 3 sine waves of 12.7, 7.1 and 4.7 Hz, is applied incrementally:

frame->F0hz10 = frame->F0hz10 + (long) delta_f0;

But according to the Klatt 1990 paper, the computed value is already the absolute F0 delta at a specific point in time. It's not a value that has to be integrated over time. The integration has the effect, that F0 wanders around unlimited.

I'm assuming that Klatt never released the source code of this F0 frequency modulation, so we can't refer to the original source code.