Envelope Filter

[Rayman]

Can anyone suggest how to modify an envelope filter so that the sweep doesn't start immediately when picked, kind of a delayed response to start the sweep when a note is picked.

[rousejeremy]

Yeah, it's called a wah pedal . What kind of Envelope Filter do you have?
Check out Technology of the Envelope Filter here http://www.geofex.com/

[CynicalMan]

Can anyone suggest how to modify an envelope filter so that the sweep doesn't start immediately when picked, kind of a delayed response to start the sweep when a note is picked.

You need an attack control. Adding a variable resistor in series with the decay capacitor is the easiest way to have an attack control. For example, http://www.home-wrecker.com/nurse-quacky.html

What envelope filter are you building?

[Rayman]

I've actually built a few (Nurse Quacky, Phuncnosis (sp), and many variations and experiments) - as well as purchased (Guyatone WR-3, Boss AW-2, FT-2).  I also have a few wah pedals (cry baby, Morley NSW, Bad Horsie).  My favorite envelope filter is the Boss FT-2.  The manual control I don't use as I like the Morley Bad Horsie (first version) for that.  I was wondering if there was a way of providing a "significant" slow attack so the sweep would start gradually, like I can do on a wah pedal.  I've never tried an envelope filter / autowah that I thought had an attack control that I liked.  Attack controls I've tried only had very minor change.  I was wondering if anyone knew of a way to provide a good "slow" attack.

[CynicalMan]

I don't know if this would be a big enough change for your tastes, but one mod I've done for the Phuncgnosis is adding a switch that changes the 1uF capacitor to ground to a 0.22uF one. This reduces the decay but lengthens the attack, giving a "pop"-like attack.

[StephenGiles]

Can anyone suggest how to modify an envelope filter so that the sweep doesn't start immediately when picked, kind of a delayed response to start the sweep when a note is picked.

A BBD in the side chain would do the trick. and noise would not be a problem!

[puretube]

Can anyone suggest how to modify an envelope filter so that the sweep doesn't start immediately when picked, kind of a delayed response to start the sweep when a note is picked.

A BBD in the side chain would do the trick. and noise would not be a problem!

Or a PT239x or a simple Spin-thingy... (stereo!) 

[Rayman]

Stephen,

Can you explain what you mean by a  BBD in the side chain?

Thanks

[Mark Hammer]

What he means is that the rectified envelope signal which forces the filter to sweep would be delayed by a certain amount of time.

But I'm not sure that's the nature of the request.  There is a difference between "pick".............................bwow, and "pick"..boooooooooooowwwwoooooooooooowwwwwww.  My sense is that you want the latter.

The hard part here is stretching out the envelope by adding enough lag but not so much that it "smudges" the sweep.  Normally, it would be important to buffer the envelope detector/rectifier in order to add more lag, and still have enough envelope signal to provide a reasonable sweep.  Alternatively, one could use a trigger generator and use that to kickstart a fixed envelope or "transient" generator.  If that interests you, I suggest taking a look at the AMS-100 project posted in the back issues of DEVICE at my site: http://hammer.ampage.org

[Rayman]

Mark,

You're exactly right, I'm looking for the latter.  I'll take a look on your site.

Thanks (once again)

Ray

[StephenGiles]

So in envelope generator jargon we are looking at hold/attack/decay perhaps, which could be achieved by cmos and/or 555 trickery - you pick a note, a capacitor is immediately discharged. After a preset time (the hold period) the capacitor is charged up to a preset voltage level (attack) then allowed to discharge - but not completely, to another preset voltage level (decay) and held there until another note is picked and the whole procedure starts again.  

There are good reasons for discharging a capacitor before it starts it's work rather than charging it up first - which I have seen in print, possibly something to do with current requirements.

And see #15 http://www.diystompboxes.com/smfforum/index.php?topic=80111.msg664143

Could possibly be adapted.

Any views Ton?

[oldrocker]

Would the envelope filter mod for the Nyquist Aliaser work?  Mine seems to sweep up slowly and dragged out.  Not sure how that could be incorperated to an auto wah though.

[StephenGiles]

So in envelope generator jargon we are looking at hold/attack/decay perhaps, which could be achieved by cmos and/or 555 trickery - you pick a note, a capacitor is immediately discharged. After a preset time (the hold period) the capacitor is charged up to a preset voltage level (attack) then allowed to discharge - but not completely, to another preset voltage level (decay) and held there until another note is picked and the whole procedure starts again. 

There are good reasons for discharging a capacitor before it starts it's work rather than charging it up first - which I have seen in print, possibly something to do with current requirements.

And see #15 http://www.diystompboxes.com/smfforum/index.php?topic=80111.msg664143

Could possibly be adapted.

Any views Ton?

I found it in the H & SR Gate article:

The Trigger line is fed simultaneously both to the Hold, and to the Attack circuitry (some manufacturers put these two sections in series so that the Attack phase cannot be initiated until the Hold Circuit has been set. Such gates cannot open as fast as their manufacturers claim!).

In order to achieve extremely fast minimum attack times it is necessary to discharge the time constant capacitor, rather than try to charge it up, since momentary currents in the order of I amp are indicated, which would place an impossible burden on the power supply.

So there you go!

[Rayman]

Stephen,

I think what you are describing is exactly what I'm looking for, but I'm in WAY over my head.  I understand the basic Dr. Q circuit (thanks to this site, and Technology of...) and how to vary attack on that type of circuit.  I'm not sure how to incorporate what you are describing in the thread you mentioned.  I get the concept, but how do I apply to a filter circuit like say the Dr. Q, Nurse Quacky, etc?  Do you have any schematics of what you are talking about applied to the traditional Dr. Q type circuit?  Or maybe I missed something....

Any help is appreciated,

Thanks

[StephenGiles]

I do understand what you are saying, it's not easy. I don't have time at the moment but I intend to spend some tine on this soon.

[Rayman]

OK, thanks, I'll be looking forward to anything you can come up with.

[StephenGiles]

I do understand what you are saying, it's not easy. I don't have time at the moment but I intend to spend some tine on this soon.

I hope that's not (turpen)tine

[StephenGiles]

This died a death Must be someone out there who is on the same wavelength

[ElectricDruid]

Just to say that I agree with StephenGiles.

Many envelope filters derive the envelope directly from the amplitude of the signal going in (an envelope follower). This is great, but if you slow the attack down too much, the note will already have decayed a lot before the 'decay' part actually starts. Consequently, you finish up losing a lot of potential modulation depth. Boosting the level to compensate will also boost any remaining ripple in the envelope follower output - usually something to be avoided.
The other type of envelope filter use the guitar signal to trigger an envelope generator that is then fed to the filter. This envelope generator could be based on a 555 as suggested. This approach has its problems too (like triggering the envelope cleanly) but would probably be preferable if you want a delayed envelope like you describe.

Just my 0.02€.

T.

[StephenGiles]

Just to say that I agree with StephenGiles.

Many envelope filters derive the envelope directly from the amplitude of the signal going in (an envelope follower). This is great, but if you slow the attack down too much, the note will already have decayed a lot before the 'decay' part actually starts. Consequently, you finish up losing a lot of potential modulation depth. Boosting the level to compensate will also boost any remaining ripple in the envelope follower output - usually something to be avoided.
The other type of envelope filter use the guitar signal to trigger an envelope generator that is then fed to the filter. This envelope generator could be based on a 555 as suggested. This approach has its problems too (like triggering the envelope cleanly) but would probably be preferable if you want a delayed envelope like you describe.

Just my 0.02€.

T.

I think that I may be spared a day of visiting, being visited and generally being elsewhere over the Christmas break so I certainly hope to put my ideas to breadboard at the very least, starting with the Adaptave Peak Following Envelope Generator - you know the one - based on the Space Drum EG, but with the voltage feeding the Start Frequency buffer dependent upon the sampled Adaptave Peak Follower.