modulation waveform.
Renamed some vars for better reading.
Made the used core algorithm easier - hopefully it works and the sound is
better than before.
mod_index=*mp*(1-MODULATION_MAX_FACTOR)*_delay_length;// "(1 - MODULATION_MAX_FACTOR) * _delay_length" means: maximum bytes of modulation allowed by given delay length
mod_fraction=modff(mod_idx,&mod_number);
mod_fraction=modff(mod_index,&mod_number);// split float of mod_index into integer (= mod_number) and fraction part
// calculate modulation index into circular buffer
// calculate modulation index into circular buffer