In FM mode, what does POSTRI means?

[fsx]

Hello, I own a Virus Rack Classic so I have only one FM mode, which I believe is a POSTRI after studying the howto programming.
Being unable to compare this mode to the other modes present in newer Virus machines, can someone explain me in a very brief detail what does POSTRI means?

All I know about FM synthesis is that a modulant sine is passed through a carrier and that it changes overtones and waveform.

Thank you in advance!

FSX

[thomas]

I'n not completely sure eigther. it stands for positive triangle. I believe the other is called triangle. So with pos triangle the negative values are mirrored positive. One of the two does not affect the pitch.

[Joey]

pos tri sources the triangle wave from oscillator 1

the other tri mode is just that same triangle but inverted

[fsx]

Hey I have found the info in the INDIGO manual, the positive triangle waveform is like an absolute triangle, having only the upper part of the wave over the zero, instead the triangle goes from 0 to up and back to 0 to down cycling... (like an absolute sine wave).

Here's an extract of the INDIGO manual:

FM Mode Selects the modulator for oscillator 2.
Choices are:
• PosTri: frequency modulates oscillator 2 with
a positive triangle waveform generated by os-
cillator 1.
• Tri: frequency modulates oscillator 2 with a
triangle waveform generated by oscillator 1.
• Wave: frequency modulates oscillator 2 with
the waveform currently selected on
oscillator 1.
• Noise: frequency modulates oscillator 2 with
the noise generator.
• Input: frequency modulates oscillator 2 with
the audio of the track on which the Indigo
plug-in is currently inserted. If the audio is a
stereo signal, only the left channel is used. If
there is no audio signal on the track, no mod-
ulation is applied.

[annikk.exe]

• Wave: frequency modulates oscillator 2 with
the waveform currently selected on
oscillator 1.

Ooh!

Didn't know that.. :>
I always assumed by "wave" it meant a sine wave..for some reason.


-Annikk

[Timo]

I thought "Tri" is bi-polar, going from negative (-ve) to positive (+ve) through 0 and vice versa, whereas "Pos-Tri" is a positive waveform only.

As below:



A bit like the difference between AC and DC electricity.