you're right that is confusing. I fixed it, but actually a better version of this description can be found in the download section: Nord Stage – How to use the Virtual Analog Synth
Basically, it refers to creating synth sounds with two detuned oscillators using the noise generator with full resonance which basically creates a sine wave and then the cutoff sets the frequency. The formula just computes the frequency from the desired interval. dx=7 semitones means a relative difference in frequency of (2)^(7/12)=1.49 so that the frequency of a fift is 49% over the fundamental. Since 330Hz at the Nord is calibrated to sound like A4 (or that the cutoff displayed is the one applied on the note E1 (obviously the cut off frequency varies across the key range unless keyb tracking is completely disabled, so the displayed value needs to be choosen to represent one key), you need to increase the cut-off fequency to 330*1.498=494Hz to have the sine sound one fifth over the fundamental (e.g., piano sound or second panel synth sound).
In the welsh Cook Book they give many sound description containing two detuned oscillators (e.g., by 8 semitones and 5 cents for the harmonica sound), which can be programmed roughly this way.
Sorry if it wasn't all clear.
(Note: Exp would be the exponential function, but technically it's a twelfth root, fixed in the doc. The 502 Hz is the value for 8 semitones and 7cents (not 5, sorry my error) (approx) indeed and refers to information given in the Welsh Cook book, see here:
- harmonica_synth_welsh.png (53.31 KiB) Viewed 9911 times