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Syncing the LFO
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Syncing the LFO
catchin
Help! Maybe some of you seasoned modular folks can help me. I want to have a filter frequency CV move in time with a sequence. So let's say I have 8 steps, and I want an LFO saw wave sweep frequency from step 1 to step 4, and repeat in sync with the gate. How do I do this?

I've tried a step splitter, that resets the LFO but it never stays in time with the beat so the slope of the LFO is all over the place.
hw408
Not an expert but I would end up sending the gate when I want the LFO cycle to restart, and manually adjust the rate until it fits.

Is there another way to lock in a LFO rate to a tempo?
BenA718
I have an LFO that is sync-able (SSF/WMD Modbox). Made my life so much easier!!!
authorless
1) What is a "step splitter"?

2) Why not use an envelope?

3) What LFO?

4) There are LFOs that sync to a clock. 4ms QPLFO is one.
Dave Peck
Any standard audio osc that has a hard sync input and that can operate as an LFO will also work. Set the LFO close to the correct rate and connect the clock out to the hard sync in. Hard sync input on an audio osc is the same thing as a reset input on an LFO.
hw408
. i had forgotten about that feature of Modbox, that was a nice reminder. thumbs up
luketeaford
I would do this with a fast master clock.

Clock the sequencer 1:1 with master clock. Reset the LFO at /4 of master clock.

The fast master clock strategy makes it a little easier to change tempo (to something related). It's easier to use slew/envelopes/function generator for this because a slew can keep it more consistent than an LFO which may reset but won't hit its target end point with tempo changes and may go past it.
catchin
authorless wrote:
1) What is a "step splitter"?

2) Why not use an envelope?

3) What LFO?

4) There are LFOs that sync to a clock. 4ms QPLFO is one.


1) That thing that takes a clock and splits into 16ths, 8ths, quarters, etc...

2) Never thought of using an envelope. Will try it out.

3) Doepfer A-145

4) Thanks for the recommendation
mritenburg
catchin wrote:


2) Never thought of using an envelope. Will try it out.



Envelope is the way to go. Take a divided clock that is high for the duration you want to sweep the filter frequency. Use that clock to trigger your envelope, then use attack and decay settings to control the sweep up and down.

Clock work.
Dave Peck
catchin wrote:
authorless wrote:
1) What is a "step splitter"?



1) That thing that takes a clock and splits into 16ths, 8ths, quarters, etc...


This is called a "clock divider" module.
Rex Coil 7
Dave Peck wrote:
Any standard audio osc that has a hard sync input and that can operate as an LFO will also work. Set the LFO close to the correct rate and connect the clock out to the hard sync in. Hard sync input on an audio osc is the same thing as a reset input on an LFO.
SAYS THE GLARING RED NEON SIGN

LISTEN TO THIS MAN
catchin
I think what I want is something similar to what Peaks does, but watching some videos on it doesn't really assure me that it's doing what I need.

Most LFOs do a hard reset when triggered by the clock, meaning that I would have to find that perfect LFO period by adjusting the pot by hand (good enough but not perfect). I think what Peaks is doing is finding the amount of time between 2 triggers of the clock, and using that to set the LFO wave period to match that length, which is exactly what I think I want.

Are there any modules that do that?
soon_come
catchin wrote:
I think what I want is something similar to what Peaks does, but watching some videos on it doesn't really assure me that it's doing what I need.

Most LFOs do a hard reset when triggered by the clock, meaning that I would have to find that perfect LFO period by adjusting the pot by hand (good enough but not perfect). I think what Peaks is doing is finding the amount of time between 2 triggers of the clock, and using that to set the LFO wave period to match that length, which is exactly what I think I want.

Are there any modules that do that?


There are, but I can't remember which. I mean... Peaks does it, I'm pretty sure. What you're referring to is a different type of sync/reset, usually called "clocked LFO" or pingable LFO or something like that. What it does (like many tapped delay pedals) is average your last X taps to generate a pulse wave (clock signal) on time. This way, if you're sending it regular triggers, it will keep time and adjust if the tempo changes, for example.

Using the more primitive method (reset input) wouldn't ever "stretch" the wave over time like you want. You'd have to adjust the frequency of the LFO accordingly, because the only reference point you have is the start point.

But if you're not changing tempo or doing anything particularly weird, I wouldn't worry about it not being perfect. Get it sounding right and leave it alone hihi
luketeaford
Even if you are going to change the tempo, I think it's still easier to use a fast master clock. You can then change either a division of that clock or the clock itself.

Suppose you want an LFO that completes 1 cycle per 4 clocks. You just divide the master clock by 4. You then use that divided by 4 clock with an envelope generator. If you change the tempo, it will still divide by 4 just fine but some of the LFO making strategies may not work-- Maths for example doesn't retrigger during its rise stage.

This is all slightly easier with a musical clock divider rather than the mathematical one which feels out of phase to people like me who aren't electronics wizards.

Is there something I'm overlooking that makes the fast master clock strategy not work for you? What ratio of clock to LFO are you hoping to achieve?
dubonaire
mritenburg wrote:
catchin wrote:


2) Never thought of using an envelope. Will try it out.



Envelope is the way to go. Take a divided clock that is high for the duration you want to sweep the filter frequency. Use that clock to trigger your envelope, then use attack and decay settings to control the sweep up and down.
attack
Clock work.


Totally, you don't need to be exact with the decay because it will always retrigger back to the attack phase and you don't need the timing exactitude required for a bipolar LFO. And you can experiment with the rise and fall times and maybe curve types to find what you most like.
Gaetan
My small rack doesn't have any lfo yet so I like to send a clock divider (A-160) output into a slew limiter (A-170) to achieve that. Works surprisingly well and the LFO can be shaped quite nicely.
catchin
luketeaford wrote:
Is there something I'm overlooking that makes the fast master clock strategy not work for you? What ratio of clock to LFO are you hoping to achieve?


No I don't think you are overlooking anything. I think it's me lacking the ability to conceptualize it.

I'll give the ADSR approach a try.

What I want is the filter to be swept at the rate of time of a step in a sequencer. The steps are at varying not lengths, so the sequencer gate is the trigger by which the sweep gets reset. That I can do with an LFO, but because the LFO's period is constant, yet the trigger is not, the sound I get is too choppy and disorganized. Not that I don't like the chaos, but that is not what I'm after in sense of the sound.
luketeaford
catchin wrote:
What I want is the filter to be swept at the rate of time of a step in a sequencer. The steps are at varying not lengths, so the sequencer gate is the trigger by which the sweep gets reset. That I can do with an LFO, but because the LFO's period is constant, yet the trigger is not, the sound I get is too choppy and disorganized.


Oh yeah-- envelope is a better match here than an LFO in my opinion. The goal is that the filter cutoff is at the same frequency at the end of each note even if the note is 1/4, 1/8, 1/16 etc ? That would take you there.

I didn't understand what you were attempting to do at first.
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