Attack stompbox

[ile]

Hi,

Has someone thought to build a stompbox that implements the ADSR ( Attack, Decay, Sustain, Release )?

Attack time might be pretty easy to build?
Decay time, dunno?
Sustain level, probably(?)
Release might be a harder, needs reverb...

I think a pedal that implements only the attack time might be nice. Does there exist any schems or pedals for this? Or do you have any suggestions for a design?

-Ile

[smccusker]

well an envelope filter which controlled amplitude with a compresser after it would probably get you halfway there.

[Mark Hammer]

The thing to remember is that a full ADSR envelope pattern is:

a) Something originally intended to impose dynamics on a signal that HAD none (a steady electronic oscilator), not as a means of changing the dynamic character of a signal that already had dynamic properties (attack, decay, etc.)

b) ADSR generators require something to tell them not only that a note has started, but that the note is still going.  Fortunately, with synths, a keypress is capable of providing this information.  In traditional mono analog synths, a keypress would result in a "gate" signal as well as a "trigger" signal/pulse.  The trigger indicates the *start* of the note, while the gate lasts for the entire duration of the note.  Attack/Decay (AD) generators can be used with a trigger, but it generally requires a full gate to use an ADSR-type envelope generator, at least in the analog world.

c) Producing a trigger for a guitar is reasonably easy.  Producing a gate requires more technology and more planning.  Indeed, a usable gate requires every bit as much careful planning as a decent octave divider, and for generally the same type of reason.  Keep in mind that, as noted above, a guitar note has a signal that varies over time.  As the note decays, it can often have varying levels, especially if there is any finger vibrato introduced, or the strings aren't brand spanking new.  To produce a gate, the circuit has to decide if the signal is above or below the threshold/criteria for determining that a note is "on".  Because of the inherent instability of guitar string notes, you get "false alarms" and the sputtering normally associated with bad octave dividers.  One way of compensating for this is to simply set the threshold high enough that the gate ends before the note gets unstable, but that tends to shorten the lifespan of the notes too much for many users.  A second approach is to do something to produce a more consistent volume level for the note over its lifespan.  The old Anderton comparator-based Ultra-Fuzz is a good candidate for this, as are some of Tim Escobedo's circuits.

4) An ADSR generator is always used with a voltage-controlled amplifier.  The envelope generator controls the volume of the amplifier so that a tone which is continuously on (oscillator) appears to come on and die out.  Since the guitar note actually *does* continue, a shortened gate pulse can be used to initiate the release phase of the envelope cycle, and a guitar player will still have something to "fade out" as the ADSR module gradually turns down the gain on the VCA.

5) If attack and decay are actually what you really want (and keep in mind that the full ADSR is really only to mimic the initial transient characteristics of other instruments), then some of the "Slow Gear" type pedals can accomplish that with MUCH less bother.  Better yet, build a Slow Gear from the posted layout/PCB over at GGG.

In the meantime, here are some files that may be of interest to you, especially the last two, which are from an Anderton article in 1983 Keyboard magazine for extracting a usable trigger and gate from an external instrument source.

http://www.synthdiy.com/files/1/2004220/PAIA_2720-11_Env_Follower.gif
http://www.synthdiy.com/files/1/2005421/ar.gif
http://www.synthdiy.com/files/1/2005421/4740adsr.gif
http://machines.hyperreal.org/categories/do-it-yourself/schematics/TRIGfig1.JPG
http://machines.hyperreal.org/categories/do-it-yourself/schematics/TRIGfig2.JPG

[SonicVI]

If you're only looking to control volume it would probably be far simpler to just use a volume pedal.

[Paul Perry (Frostwave)]

Often what people really want is a way to 'automagically' screw with the envelope.
If you were to run the input thru a compressor, and simultaneously to an envelope follower, it should be possible to mistreat the envelope (slew limiting, lag processing, non-linear transforms, clipping etc) and then via a voltage controlled amplifier, enforce the 'processed' envelope on the compressed signal.

[petemoore]

I couldn't do it on my own very easily...
 But what are you going to do with it?
 Palm muting does that.
 Here's the application idea I get from the concept
 Use the pulse detector to 'inject' some other tone for limited time during/after the note pulses enough to activate the detector.
 Reversing the 'on/off' of the pulse envelope would make it like a compressor...
 Alot of Fuzz and Attack isn't too hard to get using just a couple or few or more of transistors
 I would think the output of the FF might make a very interesting sounding envelope detector driver, the seem naturally able to go loud/soft, loud with heavy attack, medium with loud on hard attack, quiet with medium using more than 1 string, using picking strength and Guitar volume.
 Might be tricky having to get around using an input buffer to drive the signal path through x circuit and the sidechain to get all the variances of the FF>Efollower...
 Just typing because it seems feasable...
 I would think alot of usable voltage responses from an input gained FF, compared with just a buffer or booster.