Please explain the function of a Low Pass Gate?

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georgehruiz
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Post by georgehruiz » Thu May 24, 2018 3:10 pm

This has been an incredibly instructional thread. I feel like I'm meeting my Optomix for the first time. Thanks everyone!!

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GuyaGuy
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Post by GuyaGuy » Thu May 24, 2018 3:17 pm

The main function is that it lets you bring up the word vactrol. Because it's fun to say vactrol.

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tappazee
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Post by tappazee » Fri May 25, 2018 6:51 am

this is helping me get to the bottom of my RYO Aperture:) never fully understood it but love the sound of it chopping between klang (equivalent to strike on optomix I assume) and CV inputs.

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dthorn
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Post by dthorn » Mon May 28, 2018 7:15 pm

starthief wrote:
dthorn wrote:My A-101-2 hardly rings at all if I feed it a short pulse, but responds very well to stepped CV from a sequencer, like it has a weird unpredictable slew limiter built in.
Hmm, I'll have to try that :tu:
https://soundcloud.com/xebico-audio/vactrol-decay

In this patch, the CV out from the upper row of a Doepfer Dark Time is patched to a VCO and the unattenuated CV input of the A-101-2, and random gate pulses from the lower row are sent to the A-101-2's attenuated CV input, with the input level starting at zero and increasing around the 30 second mark. The vactrol decay effect can be heard in the twang after the high note, and in the nice bouncy sounds that start to happen when I turn the level up on the random gates.

The kick drum is an A-101-1 vactrol VCF being pinged at the cutoff CV input by a very short pulse from an A-171-2 VCS.

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Post by hermbot » Mon May 28, 2018 9:10 pm

I was going to talk about low pass gates at some point anyway, but this discussion in this thread made me kick of this video sooner than later...

[video][/video]

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Re:

Post by vqlk » Tue Jun 09, 2020 11:53 pm

hermbot wrote:
Mon May 21, 2018 12:26 pm
So a VCA is just a volume control, right? If you plug in the original source and turn the knob all the way down, the input signal is fully attenuated and goes away.

A filter (VCF) can do the same thing, if you turn it down far enough. If you lower the cutoff frequency eventually you'll attenuate all of the original audio, so the signal will be gone.
does it achieve this merely by the filter shape?

i think i get the basic sound from wackelpeter's soundcloud... a bit like a paralyzed vocoder ?
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Re: Please explain the function of a Low Pass Gate?

Post by ndkent » Wed Jun 10, 2020 12:33 am

Historically back in the 60s for the Buchla 100 system, Don did not combine the lowpass filter and gate switchable in one module. He had a 110 Gate which would be the equivalent of a fast acting VCA and he had a separate vactrol style (hand rolled) slow acting 192 lowpass filter. Only later for his 200 system did he do the now famous vactrol based 292 LPG with the LP, gate and both options.

If one is keeping "West Coast" score, in the early 70s, Serge called his VCA a Gate and was not vactrol based. He had a separate multimode filter, while not vactrol based I think you set it to resonate, send it a "ping" trigger, you'd get a bit of a resonant ring on it's own.

Anyway so new analog synths came back in the 90s, only a scant few had a Buchla, so everyone was making more synths like the Moogs, Rolands, etc they knew. It wasn't until the 00s you had some builders looking at those don't understand them Buchla modules with their LPGs, etc that weren't widely known. Then of course Buchla came back with their 200e and of course the calls of "I want some low cost West Coast in my euro rig too!"

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Re: Re:

Post by ndkent » Wed Jun 10, 2020 12:52 am

vqlk wrote:
Tue Jun 09, 2020 11:53 pm
hermbot wrote:
Mon May 21, 2018 12:26 pm
So a VCA is just a volume control, right? If you plug in the original source and turn the knob all the way down, the input signal is fully attenuated and goes away.

A filter (VCF) can do the same thing, if you turn it down far enough. If you lower the cutoff frequency eventually you'll attenuate all of the original audio, so the signal will be gone.
does it achieve this merely by the filter shape?
VCA (Gate) is an voltage controlled amplifier, only "open" all the way it's unity, original volume, less voltage eventually "closes" it, no audio. Opening or closing does not change the tone color.

VCF if it's say a low pass filter means a slope of audio below the cutoff frequency goes through, I say a slope because it's not an all or nothing. What's being said is if the cutoff frequency gets really low, for all intents none of the audio is passed. Huge difference though is the filter has a slope, as it goes down the tone color changes. It's not a given a filter can go that low to filter everything

Both mode (Low pass and gate) like it says, both going at the same time, so the amplitude goes down and the high frequencies roll off

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Re: Re:

Post by vqlk » Wed Jun 10, 2020 12:56 am

ndkent wrote:
Wed Jun 10, 2020 12:52 am
vqlk wrote:
Tue Jun 09, 2020 11:53 pm
hermbot wrote:
Mon May 21, 2018 12:26 pm
So a VCA is just a volume control, right? If you plug in the original source and turn the knob all the way down, the input signal is fully attenuated and goes away.

A filter (VCF) can do the same thing, if you turn it down far enough. If you lower the cutoff frequency eventually you'll attenuate all of the original audio, so the signal will be gone.
does it achieve this merely by the filter shape?
VCA (Gate) is an voltage controlled amplifier, only "open" all the way it's unity, original volume, less voltage eventually "closes" it, no audio. Opening or closing does not change the tone color.

VCF if it's say a low pass filter means a slope of audio below the cutoff frequency goes through, I say a slope because it's not an all or nothing. What's being said is if the cutoff frequency gets really low, for all intents none of the audio is passed. Huge difference though is the filter has a slope, as it goes down the tone color changes. It's not a given a filter can go that low to filter everything

Both mode (Low pass and gate) like it says, both going at the same time, so the amplitude goes down and the high frequencies roll off
cool, yeah that would be like a miracle really i guess
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Re: Please explain the function of a Low Pass Gate?

Post by Pelsea » Wed Jun 10, 2020 2:05 pm

You might want to try a high pass gate-- that's a high pass filter tuned above the input with an inverted envelope. It takes a bit of fussing to get everything tuned right.
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Re: Please explain the function of a Low Pass Gate?

Post by transistorresistor » Tue Jun 23, 2020 12:13 am

great thread, this cleared up alot of terminology for me.

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Re: Please explain the function of a Low Pass Gate?

Post by 3hands » Tue Jun 23, 2020 7:29 pm

Random LPG question.

I’m using the Borg filter in VCA mode, and I love the idea of the LPG that I want a dedicated one in euro. What would be some modules that would give me that classic ring?
Thanks in advance!
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Re: Please explain the function of a Low Pass Gate?

Post by wuff_miggler » Tue Jun 23, 2020 8:19 pm

Doepfer A-101-2 LPG is awesome:
viewtopic.php?t=45170

there is comment on that thread that it sort of doesnt "shut" completely - i am assuming i have more to learn about its best settings.
it can resonate like a banshee :P

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Re: Please explain the function of a Low Pass Gate?

Post by cptnal » Wed Jun 24, 2020 12:26 am

wuff_miggler wrote:
Tue Jun 23, 2020 8:19 pm
Doepfer A-101-2 LPG is awesome:
viewtopic.php?t=45170

there is comment on that thread that it sort of doesnt "shut" completely - i am assuming i have more to learn about its best settings.
it can resonate like a banshee :P
Mine closes fine. Vactrols, innit. :miley:
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wuff_miggler
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Re: Please explain the function of a Low Pass Gate?

Post by wuff_miggler » Wed Jun 24, 2020 12:38 am

i think i need to just sit with it more :-) its probably totally fine :P

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Re: Please explain the function of a Low Pass Gate?

Post by vqlk » Wed Jun 24, 2020 1:46 am

wuff_miggler wrote:
Wed Jun 24, 2020 12:38 am
i think i need to just sit with it more :-) its probably totally fine :P
one only needs to sit with modules that blink, haha
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Re: Please explain the function of a Low Pass Gate?

Post by snakejaw » Sun Jun 28, 2020 10:49 am

https://intellijel.com/shop/eurorack/1u/passive-lpg-1u/

I found this description from Intellijel very helpful. And it's great news!

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Re: Please explain the function of a Low Pass Gate?

Post by stepvhen » Wed Jul 01, 2020 12:42 pm

My Meng Qi DPLPG is one of my favorite modules so far. Passive, 2hp and it does exactly what its suposed to. Its possible to tune an envelope into a similar response, but why reinvent the wheel when the wheel is cheap and 2hp?

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