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Serge NTO FM observation
MUFF WIGGLER Forum Index -> Buchla, EMS & Serge  
Author Serge NTO FM observation
theboddy
OK hands up everyone who likes FM of a pitched oscillator?

I just wanted to run this past you guys. It may seem obvious but I refer to the following quote on the Egres site in the section on the Dual Oscillator (NTO) M-module. And I quote:

Dynamic depth frequency modulation is now available to the analog synthesist. Frequency modulation (FM), the modulation of one oscillator by another, generates both harmonic overtones (found in most acoustic instrument sounds) and non-harmonic overtones (bells, percussive, and electronic timbres). By varying the amplitude of the modulating oscillator, the richness or complexity of the sound can be varied. However, with conventional FM, an annoying pitch shift occurs. With the New Timbral Oscillator, Linear FM avoids this pitch shift, making it possible to maintain accurate pitch control while changing the quality of sound. A built-in VCA assures accuracy and provides dynamic voltage control of Linear FM Depth.

Sounds good. However in reality if I tune 2 NTO's to the same pitch and use one to FM the other I find that when raising the amount of FM no pitch instability is introduced until the knob is just past 12 o'clock. The the target oscillator gets progressively sharp in pitch by about 75% of a semitone by the time it's fully clockwise.

If I use say a self-cycling DTG to control the FM depth then if I attenuate it's CV signal first again I'm OK up to about 12 o'clock on the attenuating knob. After that it starts to go sharp again.

I certainly don't think this is a fault rather it's just the way it is. Question is though is this the norm one would expect with FM of this sort of do other systems hold onto their pitch better when using FM?
Navs
It could just be that the NTO allows for more lin FM than it can handle before pitching artifacts are introduced e.g. the Plan B Model 15 goes sour at about 70%. The additional modulation can be great for certain sounds, 'tho.

Another thing you could check is the tuning relationship. You say they were at unison. Could be like the detune you get when modulating a VCO by itself. Does it still happen when they're a fifth etc. apart?
Leoespejo
Ian, i can only talk about my experience with Eurorack, but having used many different oscillators, and i'd say is a "norm" or something one should expect mostly in analog devices, i haven't use ZO but making some linear FM with Hertz Donut, AFG, DPO i've experienced the same deviation in tune or at least similar.
Navs
^ exactly. On the analogue ZO and digital HzD you can 'over-blow' a thru-zero linear FM sound too.
MadGav
This sounds like the pitch of the carrier osc is being driven down to zero, where it hits the brick wall, hence raising the average (perceived) pitch (think clipping the bottom off the modulator waveform). The way round this being thru-zero, more likely than not in digital, ZO, teezer, rubicon in analogue.
Bane
did anyone made a 1on1 comparison of NTO and Rubicon?
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