Ducking delay or looping feedback(M Hammer??)

[radio]

Hi
I'm quit new here even my past knockledge of electronic and PC
does not really help.
1) Ducking delay-is it possible to achieve without RAM
2) Is having a maybe 10sec loop thats feedback while level dropping
to a certain level a possibility to achieve ducking delay
3) Looks like limiting is the (starting) key towards this quest!
Well at this point I just start tickling my brain in vage hope
this hard goal will come tru some day.

Thanks in advance for any reply and "slide" well to 2005

Enjoying your company in 2005 too

JME

[Mark Hammer]

You've touched on a bunch of things, not all of which are in the same category.  I'll answer what I can, and leave the rest to people who know more.

Is ducking delay possible?  Certainly.  Is it "hard"?  Not necessarily.

Imagine the following.  We'll use Scott Swartz' PT2399-based PT80 delay project as the point of reference.  You can find it at the generalguitargadgets website.

A ducking delay, for the uninitiated, is one in which the delay level in the mix is altered by the plentifulness and pick attack of notes played.  The idea behind it is that echoes are nice but they can occasionally clutter up the sonic landscape.  They are most enjoyed when there is space and air for them.  The goal, then, is to harness the delay level to the envelope of the input signal, such that the delay level is attenuated by some conditions, and "liberated" by others.

First off, what sort of envelope parameters?  I suspect that what one needs is a quick attack but very sluggish decay, much longer than you'd usually want for something like a compressor, noise gate, or envelope-controlled filter.  This will have the capacity to allow prolonged influence by either large numbers of notes in a short interval, or a single strong note/strum.

What sort of envelope control?  With a very long decay, a simple half-wave rectifier, like what you find on the Dr. Q, Nurse Quacky, MXR Envelope Filter, or Orange Squeezer is fine.  The big cap required will smooth out any envelope ripple. If we were going for a short decay, half-wave might be problematic but in this case we're out of trouble.

What sort of control element?  The simplest thing is either an optoisolator or a transistor to produce a variable resistance. If you go to the Rolls website and look at the manual and schematic for their DU30 ducker unit, they show a nice use of a transistor to attenuate an input signal.  They use a half-wave rectifier with a fast attack and long decay (47uf decay cap) and feed a pair of 2N3904's that each serve as a resistance to ground.

Where should delay level be adjusted?  In the case of the PT80, the best place to intervene would likely be the delay level control.  That control is a 50k pot that takes its feed from the compander chip output, and feeds an op-amp based mixer stage through a 10k resistor.  What we want to do is make that control behave like its turned down, and then turned up as you slow down or soften your playing.

If the collector of a bipolar transistor is tied to the wiper of that pot, and the emitter tied to ground, the transistor acts like a voltage-controlled resistor in paralle with that leg of the pot.  When the pot is turned way down, that parallel resistance has little impact, but when the pot is turned up, the wiper-to-ground leg of the pot is a higher resistance and so any resistance placed in parallel has a greater impact on the combined parallel resistance.  This is what we'll use.

Tying the output of the envelope follower to the base of a transistor on that leg of the pot will make the pot-plus-transistor resistance decrease with more notes or stronger playing.  If the delay level pot is turned up higher, that drop in resistance will dsramatically reduce the delay level, but let it come back to the preset level as the envelope dies out and the transistor returns to high resistance again.

Where should the envelope be derived from?  In this particular instance,  you should see "point A" on the PT80 schematic.  Since the input stage preceding point A provides a gain of 11, and does not alter the signalk more than that, the envelope follower is well situated if it takes its feed from there.  That initial gain of 11 will mean that not much more additional gain is required in the envelope follower stage itself since gains are multiplicative.  E.g.,  a gain of 50 in the envelope follower, times a gain of 11 in the first stage, will mean that the envelope is being derived from a signal that has been boosted by a combined factor of 550.  If you see the Rolls ducker circuit, you'll see that they use a pot in the envelope follower stage to adjust sensitivity.  One could probably stick another pot in parallel with the decay cap to vary release time as well, but we can work fine without it.

That is a practical working example of a ducking delay.  The envelope follower tracks large input signal and automatically attenuates how much delay signal is being fed to the output mixer stage.  AS the input signal declines in strength, the envelope signal dies out and the amount of attenuiation applied to the delay signal backs off to let the delay signal fade back in again.  Settings of the envelope follower sensitivity and initial delay level pot setting will determine the extent and feel of ducking.

Does that answer your question?

[radio]

I really am surprised by a bunch of things , especially "ancient"
control elements are sufficient. Even more lucky I am as I already have the PCB for th"PT80 with the PT2399
Moreover I have to re-read the article of Rolls ducker,and there I
made the big mistake not to consider the possibilty of 1 source
even if altered ie split up.
I understood your answer clearly ! In practice how should I start
assembling the PT80?
Could I build it up, that s my last dark point ,let s say"around" the mixer
with a loop with the purpose other effects could be easily included
like playing =>delay; pausing delay with extern phaser?

Looks like I m trying again to run upstairs 2step at once

Thank you very much indeed and "a good slide into 2005" as we
say in my country!

JME

[NaBo]

Could I build it up, that s my last dark point ,let s say"around" the mixer
with a loop with the purpose other effects could be easily included
like playing =>delay; pausing delay with extern phaser?

check out moosapotamus's very cool site cool site.
he even included a little diagram showing how he did it...
i plan on doing it to mine when i get around to making it.

here's a link:
http://www.moosapotamus.com/pt80delay/pt80delay.htm

[radio]

There s a lot of light in my project meanwhile ,thanks NaBo
I really should take a day  off to get the right start for converting
this complete input to reality.
That s what great here you mostly don t need a thread 15 answers
"long" to get info in case of lack of knockledge.
When I stopped school I hardly understood a single transistor and
moreover I stopped electronics for 20year,but then we have internet
today and suddenly you know what s inside these little boxes .
And again after 20 years motivation is greater than ever to
color music by own products.

Thanks for sharing!!

JME