Oscillator and LFO waveforms.

[ThreeFingersOfLove]

Hello,

Is there any particular reason why there isn't a saw waveform in the available range of waveforms in any of the modules? The only one is in the old H3000Osc module. I don't want to use an A_to_C module, I 'd like an LFO with saw up/down.

Also, what is the Peak LFO?

[nickrose]

ThreeFingersOfLove:

Is there any particular reason why there isn't a saw waveform

No obvious reason. You could maybe use a triangle followed by an ABS. Or use the H3000OSC, which is not at all old, and is our most versatile osc.

ThreeFingersOfLove:

what is the Peak LFO

Don't understand the question.

[ThreeFingersOfLove]

Thanks for the swift reply!

The peak LFO is the 3rd value for LFO, LFO2 and some other modules. And now that we are talking about waveforms, am I right to think that a half-sine is a rectified sine waveform? Or does it only include the "positive" part of the sine?

Regards, Yannis

[ThreeFingersOfLove]

Nick,

the ABS module is a full rectifier, i.e. it doubles the frequency of the already existing waveform. If I feed it a triangular waveform, it will probably output a triangular waveform with twice the frequency. Plus it will be offset…. Can you think of a method of deriving a triangular waveform out of a saw, or vice versa? Maybe a slew limiter with adjustable rise and fall times can give turn a tri to a saw but I don't see any module that might do this.

The peak LFO is the 3rd value for the waveforms in modules such as LFO and LFO2.

[nickrose]

The peak is like a differentiated square wave, with spikes on the edges. We think the half-sine is fully rectified.

Try connecting an LFO to a SCOPE and see for your self ..

[nickrose]

ThreeFingersOfLove:

the ABS module is a full rectifier, i.e. it doubles the frequency of the already existing waveform. If I feed it a triangular waveform, it will probably output a triangular waveform with twice the frequency. Plus it will be offset

The twice frequency should not be an issue, unless you want something over 10kHz, and you can use a hipass filter to remove the offset …

I was thinking that you could adjust the mark-space ratio to get the look you wanted. Of course, you can always use audio math modules to generate pretty much what ever you want. For example if you followed an LFO with some kind of level detector and a SWITCH driven by the detector you could create a range of sawtooth effects.

[ThreeFingersOfLove]

Hi Nick,

I am building a Barberpole phaser and I am using the H3000-Osc, because I can specify the phase offset. I have 8 such modules, which are offset as 0, 45, 90, 135, 180, 225, 270 and 315 degrees. The ABS works when you feed it a sawtooth; it outputs a triangle with half the frequency. However, not having the same frequency, doesn't help me with what I want to do. The sawtooth LFOs are used to sweep the 8 phasers and the 8 triangle LFOs are used to fade the VCA in and out. If the triangle is half the speed of the sawtooth, then the VCA will not shut completely when the sawtooth reaches the max value and so the Barberpole phasing effect is ruined.

Any idea how to double the frequency of the triangle LFO? A rectifier perhaps?

Regards, Yannis

[nickrose]

Hi Yannis – I think you are on your own here – this is essentially a research project !!

Things to think about – any amount of signal math, some kind of phase locked loop, tables and filters to generate waveforms rather than LFOs, etc etc.

[DaveFX]

All Eventides that run VSIG have sawtooth waveforms!  You can insert an audio rate OSCILLATOR or a mod rate LFO, set the waveform to a “triangle”, and change the duty cycle from the default value (0.5) to the min or max (0 or 1).  This will make a sawtooth waveform on any Eventide that runs VSIG, from the original DSP4000 up through the present flagship H8000FW.

The confusion is the synthesizer community says “triangle” to mean a triangle that is equilateral or symmetric, while VSIG says “triangle” in a more general sense of geometry (not just equilateral or symmetric).

For a barberpole effect, you can use the newer SLFO module (on the operating systems that have SLFO).  To modulate a frequency with a sawtooth: Set an SLFO waveform to “triangle” and change the duty cycle from the default value (0.5) to the min or max (0 or 1).  To modulate an amplitude with a ramp up and down: Set an SLFO waveform to “triangle” with the symmetric duty cycle (0.5) and select “unipolar” (output values between 0 and 1).  With the settings I just recommended, one cycle of a master SLFO will take your slave SLFOs through one cycle of sawtooth upsweep (for frequency) and one cycle of ramp up and down (for amplitude).

You can check everything I wrote here by making little test programs that bridge the oscillator outputs to monitor modules.  HMONITOR is my favorite because I can fit eight on one screen, which would be trippy to watch with your 8 waveforms at 0, 45, 90, 135, 180, 225, 270, and 315 degrees!  You’ll see Eight Fingers of Love!

[ThreeFingersOfLove]

Hello DaveFX!

thanks for the informative post!

DaveFX:

All Eventides that run VSIG have sawtooth waveforms!  You can insert an audio rate OSCILLATOR or a mod rate LFO, set the waveform to a ?triangle?, and change the duty cycle from the default value (0.5) to the min or max (0 or 1).  This will make a sawtooth waveform on any Eventide that runs VSIG, from the original DSP4000 up through the present flagship H8000FW.

To be honest, I have thought about the triangular waveform with the duty cycle set to 0 or 1 might produce a down or up saw, respectively, but silly me never tried it! It's nice to know that the sawtooth is there!

DaveFX:

For a barberpole effect, you can use the newer SLFO module (on the operating systems that have SLFO).  To modulate a frequency with a sawtooth: Set an SLFO waveform to ?triangle? and change the duty cycle from the default value (0.5) to the min or max (0 or 1).  To modulate an amplitude with a ramp up and down: Set an SLFO waveform to ?triangle? with the symmetric duty cycle (0.5) and select ?unipolar? (output values between 0 and 1).  With the settings I just recommended, one cycle of a master SLFO will take your slave SLFOs through one cycle of sawtooth upsweep (for frequency) and one cycle of ramp up and down (for amplitude).

You can check everything I wrote here by making little test programs that bridge the oscillator outputs to monitor modules.  HMONITOR is my favorite because I can fit eight on one screen, which would be trippy to watch with your 8 waveforms at 0, 45, 90, 135, 180, 225, 270, and 315 degrees!  You?ll see Eight Fingers of Love!

This is cool, but does the SLFO has provision to modulate it's phase? The H-3000OSC has such an input and I am using eight of these H-3000OSC modules that output 8 triangle waves (waveform = 1), and these are spaced apart by 45 degrees. These are routed to 8 slew limiters, with rise time being a 1/f, thus I can have a single LFO sweeping both the H-3000OSC modules directly and the slew limiters by a simple math manipulation. In the slew limiter, when rise = 1/f (f being the master LFO frequency) and fall = 0, it will lag the input as long as the signal rises (the ramp up of the tri) and then when the signal falls (down ramp) it will output a 0, thus a saw. The nice thing with the slew limiters is that, if rise = 0 and fall = 1/f, then I can create an ever falling Barberpole phaser (as opposed the classic ever-rising) and with a simple switch (shown as text in the LCD) I can select between the two!

Anyway, here's a jpeg of it, I was too tired to finish it yesterday. Tell me what you think!

http://farm5.static.flickr.com/4113/5042203880_a46311e4c1_b.jpg

Again, thanks for your input!

Regards, Yannis.

[DaveFX]

You’ll find SLFO is even better to make a barberpole effect.  If you investigate one SLFO set to be a master, you’ll see the sync output signal is a bipolar ramp or sawtooth (from -1 to +1).  Then each SLFO set to be a slave receives that sync signal and treats it like the timing belt on a car engine.  One cycle of the master SLFO is like one turn of a car engine crankshaft, and the slave SLFOs respond with one cycle of whatever they are programmed to do, like camshafts opening and closing the engine valves.  You can program the slave SLFOs to have the desired phase relative to the master (e.g., your 0, 45, 90, 135, 180, 225, 270, and 315 degrees).  You can “hard-code” those values of relative phase into the slave SLFOs in VSIG (and not worry about tweaking them from the front panel).  Then what you will find very interesting is patching the master SLFO frequency to a KNOB on the front panel:

• Dial the master frequency positive — your barberpole goes up.
• Dial the master frequency to zero — your barberpole stops.
• Dial the master frequency negative — your barberpole goes down.

I would break the project into two studies:

1) VSIG files to practice using SLFOs to make ramps you can see on the screen (using HMONITOR can show eight on one screen), and

2) VSIG files to check how your ear hears audio effects driven by LFOs.  The VSIG phase shifter module is an all-pass filter (flat in frequency by itself), and it needs to be combined with another signal path to make peaks and notches in frequency that we can hear.

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