Rebuilding the ADSR curve after Distortion

[Vivek]

We normally use clipping to create Distortion.

That has the side effect of compressing the signal and changing the ADSR envelope

Are there pedals that split the signal, distort one path, extract ADSR envelope information from other path

Then modulate the distorted part with the envelope information of the original signal ?

Looks like if you did this, you could have your Kate and Edith too.

[11-90-an]

i'm not sure about commercial pedals, but I would imagine you would just have to put a distortion pedal into a compressor and feed the clean, undistorted signal into the sidechain... shouldn't be that hard..

[teemuk]

Old Peavey amps (pre "Saturation" series of early 1980's) did something similar: Distortion was produced by overdring an OTA and simultaneously a side chain controlled OTA's gain with signal respective to non-distorted input signal.

I also recall seeing an envelope-controlled fuzz in some older book that presented various little electronics effect projects for musicians. Can't remember which book though.

These types of circuits have never really caught on. Maybe they sound too unorthodox. For example, multi-band distortion seems like a good idea on paper and one might wonder why it isn't more popular scheme. But in practice it converts IMD to be primarily affected by band-pass frequencies, not so much frequencies within the signal, and sounds very "synth-y" in comparison to traditional distortion with single and wider band creating IMD.

[Vivek]

https://www.youtube.com/watch?v=6nG4ofPuWTU

TWA - Wahxidizer Envelope Controlled Fuzz

[teemuk]

http://moosapotamus.net/ideas/penfold-fuzz-unit/

[Vivek]

http://moosapotamus.net/ideas/penfold-fuzz-unit/

That sounded useful and not synthetic !!!

Cannot find any video of this circuit with lead guitar

[teemuk]

I agree. It probably is much more dynamic than mere fuzz alone but it's really hard to judge from that clip. As said previously, the ancient Peavey Musician and VT series amps also employ similar idea in their distortion circuitry.

[Vivek]

If we had to redesign the circuit now,

Which VCA would you recommend ?

It might be nice to design a "dynamics restorer" and the user could use any distortion box in the loop.

[iainpunk]

there is another way to achieve this!!! my experimentation sounded quite bad since i didn't use any tone shaping and did it just for schnitzel gig-less

but here it is:

it utilizes precision rectifiers. to first take off the bottom half and then the top quarter of the input signal, independent of amplitude.

here is it at 2V

200mV

even down to 20mV


its really responsive to guitar tone and pick attack, while also being not 'cleaning up' what so ever.

cheers, Iain

[iainpunk]

If we had to redesign the circuit now,

Which VCA would you recommend ?

It might be nice to design a "dynamics restorer" and the user could use any distortion box in the loop.

i'd use a 13700, like in that penfold fuzz, since its the cleanest option out there.

[Mark Hammer]

EHX Graphic Fuzz extracted the envelope and used that to partially reconstruct the envelope of the input, post-clipping and EQ-ing.  https://www.ehx.com/products/graphic-fuzz

[amz-fx]

Paia Roctave did something similar with an NE570 as the detector and vca.

regards, Jack

[garcho]

That little book is the Maplin "Music Projects" book, by Penfold, which is where Charlie got the "Penfold fuzz unit". Penfold had a thing for envelopes, there's quite a few envelope controlled effects in there. One of them is a tremolo that kicks in as the envelope attack decays, a very musical effect, I love it.

[Vivek]

there is another way to achieve this!!! my experimentation sounded quite bad since i didn't use any tone shaping and did it just for schnitzel gig-less


cheers, Iain

Please help me understand how this circuit works

[Vivek]

How does one feed the envelope as the control voltage, and modify it such that the clipper is always giving a slight (adjustable) haircut to the signal, irrespective of the signal value

ie how to get a circuit that always clips at vPeak - 0.6v ?

[Steben]

It IS quite an interesting topic.
But it is awkward this is completely not what most search in "touch sensitivity" and "tube dynamics" : gentle compression.
And the complete oppositie of sag. 

[iainpunk]

well, its easy:
it has a 'precision rectifier'followed by another one.
the first thing that you should understand it that the op amps main goal is to have the two inputs at the same voltage all the time.
the main question is this: what does the op amp have to do to have the -input at 0V.
well, first it has to boost the signal with a static 0,6V and then the resistance dictated gain, the output is thus only the positive wave because the negative wave gets shorted out through the diode. now we only have one side of the wave. we do this again, but this time we take of the other polarity (because the op amp's inverting, the diodes point in the same direction), which is the tops of the wave and we are left with 1/4th of the the original wave shape, we also have the 2nd op amp boost a little to get to unity volume.


cheers, Iain

[Vivek]

well, its easy:

cheers, Iain

I gave you like number 300 !!!

[Vivek]

cheers, Iain

I understood it totally wrongly

[Mark Hammer]

Paia Roctave did something similar with an NE570 as the detector and vca.

regards, Jack

Good call, Jack.

As interesting as the overall topic is, and not any sort of criticism of what has been mentioned by Jack, myself, and others in the thread, I think it bears noting that "envelope followers" in general, which rectify the audio signal, provide what is essentially a representation of the relative envelope.  They do not replicate it accurately.  One probably could achieve an accurate model/representation of the original envelope, if pursued doggedly enough in the digital domain.  But let us remember here that the overarching objective of the OP, and many players in general, is simply to have a distorted sound which retains a lot of the dynamic feel and nuances of the unprocessed sound.  Aiming for more than that, in order to shape the behaviour of a two-transistor fuzz, is probably going farther than is warranted.

That said, I once again refer to the Bill Berardi "Fuzztain" circuit from Electronic Musician.  In Bill's circuit, he uses the LEDs of a pair of optoisolators as his clipping element.  However, he sits the LDR halves of those optoisolators in the feedback loop of an earlier op-amp stage to adjust and reduce the gain whenever the LEDs start to conduct.

Years ago, I suggested converting John Hollis's "Flatline" compressor to an expander, by simply shifting the location of the LDR half of an LED/LDR pair, such that when the LED is made to illuminate, the gain is increased, rather than decreased.  https://www.diystompboxes.com/smfforum/index.php?topic=95937.0   As mentioned above, it won't be an accurate replication of the original amplitude envelope, but the strategy should allow for introducing/restoring some dynamics to a clipped signal.

It does not have to be done with op-amps, although it could be.  For instance, a number of drive pedals yield greater/lesser gain for AC by varying the resistance between an emitter or source electrolytic cap (depending on whether it is a bipolar or JFET-based circuit) and ground.  Put an LDR in parallel with that resistance, and making an LED shine on that LDR during harder pick attack, will increase gain for that stage.  Of course, best to implement that strategy on any gain stage after where all the clipping occurs.