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Filter as lag processor
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Filter as lag processor
analogsplitter
Hi, I've heard that you can use a low pass filter as a lag (slew) processor. When I plug my input cv signal into my old paia filter the cv signal there is no glide effect (coming out the filters output). Any idea on how to make it work?
moremagic
youll need to drop the filters cutoff to sub audio raites if you want a noticeable slew effect on something like a keyboard or sequencer cv
sduck
Turn the resonance all the way down. Experiment with the cutoff setting. If it's a state variable design you probably want the lowpass out, although other outs may also have desirable effects.
diophantine
Is there no signal coming out, or is it just the original signal coming out.

In the former case, the filter input could be AC-coupled.
analogsplitter
Sorry, forgot to mention that the low pass output actually reverses the cv signal (so there is a signal getting through). Even with the filter set at the lowest setting, I'm not hearing any lag. Is there a trick to dropping the frequency of the filter lower?
Dave Peck
Sure, just patch a negative DC voltage to one of the filter's CV inputs to drive teh cutoff frequency even lower. sending -5V DC to the filter will drop the cutoff frequency five more octaves.

And if you're noticing that the CV is getting inverted, this is probably because it's a 12dB per octave filter, correct? Most 12 dB filters will invert the output.

BTW, just to be clear, this trick of passing a CV signal through a filter with a very low cutoff should cause a CV signal that has sudden transitions to now glide between those levels, so a square wave from an LFO, which would normally cause an audio osc to 'trill' between two notes when applied to the osc's pitch mod input, will now behave more like a sine LFO, causing the audio osc to have a vibrato effect.

If it's not doing that, can you explain exactly what happens when you send a square wave LFO through the filter and then control an audio osc with the output of the filter?
BugBrand
Yes, try a negative DC voltage to freq-mod input.
Or you could increase the value of the integrator caps -- I have that as a switchable option on half of my Dual Filter module & think it was an option on some Serge VCFs.

Dave Peck wrote:
And if you're noticing that the CV is getting inverted, this is probably because it's a 12dB per octave filter, correct? Most 12 dB filters will invert the output.


That is not exactly true - I get what you're getting at, but any properly designed filter (or other processor) should give in-phase output (eg. adding inverter stages if necessary).
analogsplitter
Great, that did it. I ran my old paia cv source (negative cv) into the filters cv input and the filter magically became a lag.
End result... I can now get my alesis andromeda to sound like the ring modulator on the Yamaha cs-80 (I needed a cv input, to smoothly control the A6 carrier frequency down to lfo rates).
Sideshow
I guess what happens when you use a filter as lag processor is baically something like this:
Videographics
Has anyone ever come out with a small and cheap Eurorack “Time Compensated Glide” module based on a simple low pass filter that’s already setup to filter at control frequencies? This omission in the market seems strange when this was so commonly done for the glide circuits on early synths.
Dave Peck
Yup there are plenty of dedicated slew generator modules that do this.
moremagic
Videographics wrote:
Has anyone ever come out with a small and cheap Eurorack “Time Compensated Glide” module based on a simple low pass filter that’s already setup to filter at control frequencies? This omission in the market seems strange when this was so commonly done for the glide circuits on early synths.
maths Miley Cyrus
Videographics
Dave Peck wrote:
Yup there are plenty of dedicated slew generator modules that do this.


moremagic wrote:
Videographics wrote:
Has anyone ever come out with a small and cheap Eurorack “Time Compensated Glide” module based on a simple low pass filter that’s already setup to filter at control frequencies? This omission in the market seems strange when this was so commonly done for the glide circuits on early synths.
maths Miley Cyrus


In my experience this is a common misconception and very few function generators actually include time compensation. There may be others but the only function generator I’m aware of with time compensation is the WMD/SSF MiniSlew. If you use Maths or Rampage or most other function generators to add glide to a sequencer or keyboard, the glide time between notes will depend on the distance between the notes. Conversely, when doing glide with a filter as we’ve been discussing, the amount of time between any two notes will always be the same, and this is generally more desirable in performance.
moremagic
Videographics wrote:
Dave Peck wrote:
Yup there are plenty of dedicated slew generator modules that do this.


moremagic wrote:
Videographics wrote:
Has anyone ever come out with a small and cheap Eurorack “Time Compensated Glide” module based on a simple low pass filter that’s already setup to filter at control frequencies? This omission in the market seems strange when this was so commonly done for the glide circuits on early synths.
maths Miley Cyrus


In my experience this is a common misconception and very few function generators actually include time compensation. There may be others but the only function generator I’m aware of with time compensation is the WMD/SSF MiniSlew. If you use Maths or Rampage or most other function generators to add glide to a sequencer or keyboard, the glide time between notes will depend on the distance between the notes. Conversely, when doing glide with a filter as we’ve been discussing, the amount of time between any two notes will always be the same,
i think the livewire one works like that
Quote:
and this is generally more desirable in performance.
i cant even imagine
Videographics
Haven’t y’all ever been frustrated when you setup a function generator to glide nicely between small intervals in a sequence, and then feed it a big interval only to find never has time to complete the transition before it’s time for the next note?
luketeaford
Videographics wrote:
Haven’t y’all ever been frustrated when you setup a function generator to glide nicely between small intervals in a sequence, and then feed it a big interval only to find never has time to complete the transition before it’s time for the next note?


Honestly I am not certain my ears are discerning enough for that!

Would it work if you used the pitch (pre slew) signal to decrease the slew time?

I think it might be a constant rate on Rene 2 when notes are set to glide.

I think the Serge NTO portamento input may also be constant time.

Going to play with this and see first if I can hear it, if I care, and if I can do what you're suggesting.
moremagic
Videographics wrote:
Haven’t y’all ever been frustrated when you setup a function generator to glide nicely between small intervals in a sequence, and then feed it a big interval only to find never has time to complete the transition before it’s time for the next note?
i drop glisses on everything, any instrument i play. cant even help myself hihi
if i want my VCOs to reach the next note i set my glade faster than my tempo or just patch straight from the keys or sequencer to them
i tried to imagine a scenario where id care about an osc hitting a note and it not getting there but uh, i can only imagine what i can imagine i guess

when i set maths to take forever the point is so whatever i patch it to will be playing catch up with the rest of the patch: if it gets there, cool; if not, theres other notes, other patches
Videographics
Well, maybe try to imagine Keith Emerson’s solo at the end of ELP’s Lucky Man without time-compensated glide. If the glide was set for the small intervals, lot of the notes following the wide intervals would never be heard, and if it was set for the wide intervals, you’d wouldn’t hear glide hardly at all on the small intervals. Apparently Keith was having so much trouble playing musical solos with glide that wasn’t time-compensated, Bob Moog ended up doing it as a custom mod for him. And then it became fairly standard on most keyboard-based performance synths because it was so much more musically useful.

Check out the poll at the top of this page: https://www.gearslutz.com/board/electronic-music-instruments-and-elect ronic-music-production/1073581-preferred-glide-constant-rate-constant- time.html At the time of this posting, time-compensated glide was preferred more than three to one!

Time-compensated glide is pretty important for many of us using glide/portamento to process a note-based controller. And it’s a very musically useful option for anyone interested in playing both large and small intervals with glide. I’ve got well over a dozen slew limiters at my disposal, but for glide/portamento on a keyboard or other note-based controller, I pretty much always use the Mini Slew or a filter-based glide to keep things musical. I think folks who don’t play keyboards should consider or at least be aware of this.

And, lastly, if it can be done with a super simple (and very inexpensive) filter circuit, does it make sense to waste a function generator on this?
flo
ADDAC also make a small time compensated glide, I don't have it but it looks nice: http://addacsystem.com/product/addac200-series/addac209 thumbs up
Videographics
flo wrote:
ADDAC also make a small time compensated glide, I don't have it but it looks nice: http://addacsystem.com/product/addac200-series/addac209 thumbs up

Yeah, nice to see a smaller module available for this. But if you really want cheap and simple, a basic filter with a voltage offset could be much more economical.

I still prefer the Mini Slew for independent control over rising and falling glides. (I’ll often set it up to glide going up with little or no glide going down. I find it more fun to play bass lines and melodies that way.)
JakoGreyshire
I was having fun the other day making a stormy wind sound... Noise in to a filter and a stepped random CV into the freq CV input of the filter... It was to abrupt and I thought I need to slew out these steps.. What came to mind first was a vactrol... So I ran the stepped random through a low pass gate and I had to add a negative offset to the LPG as well... It worked very well...

As for the time based slew... I'm not sure it would work, but I was getting the idea for using Maths AD channels as a slew and patching an ADSR into the rise, fall, or both input on the maths channel... Maybe an inverted ADSR signal...
I haven't thought about it thoroughly though... Something where the sustain on the ADSR would hang the lag of the slew...

Would that work?
Dave Peck
Videographics wrote:
Dave Peck wrote:
Yup there are plenty of dedicated slew generator modules that do this.


moremagic wrote:
Videographics wrote:
Has anyone ever come out with a small and cheap Eurorack “Time Compensated Glide” module based on a simple low pass filter that’s already setup to filter at control frequencies? This omission in the market seems strange when this was so commonly done for the glide circuits on early synths.
maths Miley Cyrus


In my experience this is a common misconception and very few function generators actually include time compensation. There may be others but the only function generator I’m aware of with time compensation is the WMD/SSF MiniSlew. If you use Maths or Rampage or most other function generators to add glide to a sequencer or keyboard, the glide time between notes will depend on the distance between the notes. Conversely, when doing glide with a filter as we’ve been discussing, the amount of time between any two notes will always be the same, and this is generally more desirable in performance.


There are lots of synths that offer both linear and exponential portamento, and some of them offer options for either 'constant rate' or 'constant time'. So there should be modules that offer slewing as a separate function, apart from those built into a CV keyboard, that would do this too.

... actually, if I remember correctly, the keyboards that had a choice like this offered either (1) linear with constant rate or (2) exponential with constant time.
Videographics
JakoGreyshire wrote:
What came to mind first was a vactrol... So I ran the stepped random through a low pass gate and I had to add a negative offset to the LPG as well... It worked very well...

Well, that’s the low-pass filter-based response we’re talking about.

JakoGreyshire wrote:
As for the time based slew... I'm not sure it would work, but I was getting the idea for using Maths AD channels as a slew and patching an ADSR into the rise, fall, or both input on the maths channel... Maybe an inverted ADSR signal...
I haven't thought about it thoroughly though... Something where the sustain on the ADSR would hang the lag of the slew...

Would that work?

Yes and no. You might be able to approximate the response of a low-pass filter, but is it worth all that trouble? The Mini Slew is essentially a function generator that tries to do all those dynamic adjustments in an effort to make the time consistent with each note transition. It's response isn't as smooth as a filter but, it offers independent control over the rise and fall in addition to the time-compensated glide. And having this combination of features is often important to me.

But when I don't care about independent control over rise and fall, the low-pass filter is smoother sounding and a much more economical solution. You can even choose between low-pass filters with different slopes to choose the curvature of your glides while maintaining consistent time between notes. IMHO this is what gives you the best sounding glides.
JakoGreyshire
Cool, Thanks for the clarification.....

This topic just got my caffeinated brain going off on some tangent with some of the modules I have and I didn't have time to test out my theory today... nonetheless, I appreciate topics like this for the ideas they give even if the ideas miss the mark a bit...

The space between notes is now full of ideas.... And I think I can do the time domain slew with some the modules I have.. Happy patching!

Cheers!

thumbs up thumbs up cool thumbs up thumbs up
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