is a filter basically a vca

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IEC
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is a filter basically a vca

Post by IEC » Tue Aug 06, 2019 6:18 am

i realise they are not exactly the same, but can you just use a filter as a saucy vca? they both just open/close letting sound through albeit in slightly different ways right?

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Shledge
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Post by Shledge » Tue Aug 06, 2019 6:21 am

Not all filters fully close.

If it's a filter that fully closes, it's usually a low pass gate.

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Post by bibleblack » Tue Aug 06, 2019 6:35 am

As Shledge said

The main difference is on affects the amplitude of the input the other removes frequencies.

I have used filters to gate a sound much like a VCA.

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Joe.
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Post by Joe. » Tue Aug 06, 2019 6:46 am

Patch it up and find out :cloud:

ADSR into the Frequency cutoff, offset so it starts at 0hz, maybe opens up to 2-3kz cutoff at peak envelope, and then closes back to 0hz at the end.

Then try playing different notes through it :tu:

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IEC
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Post by IEC » Tue Aug 06, 2019 9:06 am

yeah this sort of routing is basically what I do a lot. in fact most of my VCA sit unused as just have developed a habit of routing sounds through a closed filter then opening it with an envelope. just wondering if this is a normal thing to do i suppose! to my ears opening the filter does increase the "perceived amplitude" as the filter opens up, more and more sound gets through, leading me think, this is actually kind of like a VCA of sorts! i think its nicer kind of sound than a straight up amplitude envelope too ....

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paperCUT
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Post by paperCUT » Tue Aug 06, 2019 9:39 am

Watch your low end though, it'll turn to mud pretty quick if you're not closing things you think are closed.

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Post by notmiserlouagain » Tue Aug 06, 2019 9:57 am

It´s a vca that works only on selected frequencies...

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Post by gruebleengourd » Tue Aug 06, 2019 2:49 pm

Everything is just some fancy embellishment of a slew limiter.

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IEC
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Post by IEC » Tue Aug 06, 2019 4:45 pm

paperCUT wrote:Watch your low end though, it'll turn to mud pretty quick if you're not closing things you think are closed.
think all my filters close completely ... hexinverter red dragon, erica dual vcf, dual borg and the one in the tonestar 2600... a non closing filter would be rather annoying !

though i suppose i could just buy more filters and run everything through a hpf first to close off the leaky bit :omg:

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Post by ersatzplanet » Tue Aug 06, 2019 5:32 pm

A filter will work as a VCA when it is a LP and can be pitched below the range of hearing which will always be below the frequency of the sound you are hearing but of course it is more than just changing the volume level, it is also changing the timbre. If you have a bright sound, and you want it to stay bright, and want to control the volume and volume only, then you need a VCA. I often use VCFs to do both jobs when I don't have a VCA to use but then I commonly have level control at some point allowing the volume to be changed without changing timbre.

Typically the best filters for this are Low Pass filters with a sharp cutoff (24dB/oct or better) and to avoid too much timbre shifting, little or no resonance.
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IEC
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Post by IEC » Wed Aug 07, 2019 2:07 am

thats interesting, the one i use the most is a 6db/oct lpf for doing this, as it sounds a lot more interesting when the cutoff is still fairly low ... I find with steeper slopes it almost seems like you lose a lot of the sound and unless you open the filter up quite a bit it can come across as being a bit quiet. i typically dont use much resonance like you suggest.

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Post by ersatzplanet » Wed Aug 07, 2019 12:09 pm

IEC wrote:thats interesting, the one i use the most is a 6db/oct lpf for doing this, as it sounds a lot more interesting when the cutoff is still fairly low ... I find with steeper slopes it almost seems like you lose a lot of the sound and unless you open the filter up quite a bit it can come across as being a bit quiet. i typically dont use much resonance like you suggest.
The cutoff slope will effect the timbre change when clamping down the audio for sure. The low cutoff slopes will be heard less as the cutoff acts as a long attenuation "tail". The problem is lots of filters will not tune low enough when they have a shallow cutoff to fully attenuate bass sounds. With a sharper cutoff, you will hear high end harmonics go before the fundamental is clamped. I tend to use this a a feature but there are times when you really want to avoid going over the fundamental frequency with the filter (especially with any resonance applied).
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Post by moremagic » Thu Aug 08, 2019 2:41 am

IEC wrote:thats interesting, the one i use the most is a 6db/oct lpf for doing this, as it sounds a lot more interesting when the cutoff is still fairly low ... I find with steeper slopes it almost seems like you lose a lot of the sound and unless you open the filter up quite a bit it can come across as being a bit quiet. i typically dont use much resonance like you suggest.
yeah, i use the sport mod as a vca often enough, since its right above my output module. the 6dB rolloff adds a nice tonal variation but its not as hushed as ladder filter

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Post by SB-SIX » Thu Aug 08, 2019 3:21 am

Shledge wrote:Not all filters fully close.

If it's a filter that fully closes, it's usually a low pass gate.
Not all VCA's fully close too :) (had some awful vca's with bleed in the past)

Most of my filters fully close (e440, sob, borg, aperture, doepfer SEM) but some don't. I think Polaris is my only filter that does not close fully with the cutoff knob, but at least it has a level knob to fully close it.
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Post by Manresa » Fri Aug 09, 2019 10:38 pm

Don’t forget that VCAs are also extremely useful for attenuating CV, and a filter is going to be less useful for that.

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Post by jacup211 » Fri Aug 16, 2019 2:00 am

Off course you may want to use both in series. This gives an extra level of control fort tone shaping. Most non modular synths have envelopes for the VCAs and the VCFs. Shaping attack and decay times first through a VCA and then on top of that with one or more Filters will give a more ˋnaturalˋ sound.

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Post by SB-SIX » Fri Aug 16, 2019 4:51 am

Manresa wrote:Don’t forget that VCAs are also extremely useful for attenuating CV, and a filter is going to be less useful for that.
Good point! About half of my filters are DC coupled (can't remember which ones). An AC coupled filter is quite useless for CV but a DC one it actually quite handy. It will slew the signal and attenuate when slewed enough
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Post by naturligfunktion » Fri Aug 16, 2019 6:02 am

Manresa wrote:Don’t forget that VCAs are also extremely useful for attenuating CV, and a filter is going to be less useful for that.
something that in my opinion makes VCAs increadibly useful

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Post by Manresa » Fri Aug 16, 2019 10:29 am

SB-SIX wrote:
Manresa wrote:Don’t forget that VCAs are also extremely useful for attenuating CV, and a filter is going to be less useful for that.
Good point! About half of my filters are DC coupled (can't remember which ones). An AC coupled filter is quite useless for CV but a DC one it actually quite handy. It will slew the signal and attenuate when slewed enough
Interesting! I’ll try that out. You wouldn’t happen to have any links to describe what’s happening in detail?

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Post by oberdada » Thu Aug 22, 2019 3:08 pm

Highpass filters would be about as useful for this as lowpass. It depends on the input's bandwidth, the cutoff frequency and the filter's steepness. But then you'd have to watch out for younger / more acute listeners who hears all the way up. And if the signal is used as, say, an FM modulator source, inaudible audio content will still cause audible modulation.

And what about a highpass gate? Probably not as useful as the LPG which mimics the covariation of amplitude and spectral brightness in most natural sound sources, but maybe worth a try.

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Post by jakobprogsch » Thu Aug 22, 2019 5:13 pm

A sufficiently flexible filter can be everything. Filter and oscillator for obvious reasons. Many will happily oscillate into LFO frequencies. The flatter slope they offer the better they are as VCAs (6db/oct as found on polaris, filter8 etc. work well). Heck you can even patch them as envelopes if they are DC coupled. Patch the gate to both the input and some FM input. Now you can adjust the ratio between attack and release with the FM attenuator and the cutoff controls both times. Filters with low ranges like Filter 8 are great for this. Turning up the resonance will even provide some kind of "echo" effect. I'll claim a good filter (did I mention Filter 8?) is more flexible than Maths. 8-)

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