Question about release

[Heemis]

I really don't even know how to phrase this question exactly, but I'll give it a shot.

Basically I have a white noise generator, and I have the output connected to a momentary button type switch that I can trigger to get a little white noise hit, almost like a snare on an old drum machine.  What I want to know, is if there is any easy way to extend the release of the switch so that the sound fades away (preferably with a duration of my choosing) rather than simply cuts out. 

I am very interested in making this work, even if it's fairly difficult.  Please let me know if anyone has any ideas.

Here's a link to the white noise gen schem i'm using:  http://www.uoguelph.ca/~antoon/tutorial/xtor/xtor6/6fig7.gif

[chi_boy]

I'm sure one of the pro's will jump in here (I'm just a user), but the Echo Base delay does what you are asking about.  I remember reading that it was not true bypass and that it was designed that was so that it could incorporate fades after being turned off.

Perhaps the concept could be addapted to your application.

[oskar]

Take a peak at the MXR blubox (tonepad). The signal is feeding a simple envelope and you can create this envelope with a pushbutton instead and use the same transistor setup. Signal to base, envelope to collector... ( taking this from memory though...)

[Heemis]

Thanks for the quick replies.

Oskar, I'm looking at the MXR blue box schematic, and forgive me, but I'm not so good yet at deciphering what part of the schem is the envelope... is it basically everything after the collector of Q1?

Also, if that is the case, is R20 the control for release?

Sorry, I'm still fairly new to figuring out what part of the schematic actually does what.  Any help would be greatly appreciated.  Thanks!

[oskar]

The envelope part is what starts to the right of C7. Give it a pushbutton to V+ and C8 will charge up ( through some resistor preferably )and then charge down again through R13-R15. R15 you can substitute for a pot.
Noise enterQ3 base and envelope through R14. Output then is also on the collector through a cap.
This was the first answer that struck me and I'm not satisfied with it really. But analog drummachines have decays set up in similar fashion and this is similar to the TB-808 maracas.
Check diy synthesizer pages for better help... What you're looking for is a simple envelope AR, Decay etc...

[frequencycentral]

This will work:

[oskar]

  only 5 times better... keep it simple!

[Heemis]

I like the look of that!  Seems to be a very simple solution.  Just one more quick question, will this mean I'll need to add that op amp into the white noise generator circuit for this to work?  Or could I simply place the pot/cap somewhere into the existing circuit?  Also, where would I place this in the circuit in order to use it with the momentary switch?  I definitely plan on experimenting with this when I get back to my workbench, but at the moment I'm just trying to wrap my head around how this will work into the existing circuit.  Thanks again for the replies!

[oskar]

What you're looking for is really two things.
1. An envelope generator
2. A VCA

The envelope controls the VCA. You've got homework to do...     Google "diy modular synthesizers"
Frequencycentral's solution is a decay ( envelope ) only. It will give you a voltage out that will decay upon release of the trigger. But you need a solution to let this voltage control the amplitude of the noise. That's where the VCA comes into the picture.
I vaguely were trying to solve both problems but the bluebox envelope won't translate to your needs I'm afraid.

[Heemis]

The funny thing is, I'm actually a huge synth nerd, but I'm just new to the actual electronics involved in making them work the way they do.  I understand the way VCAs and AR, ADSR etc envelopes work from the outside, but getting to know them on the inside is where I'm having trouble.

This makes sense to me though... I have a good idea how to potentially work this into my circuit.  I should have some results later tonight.  I think I have a spare 741 op amp from a Dist + build I can use here.  Thanks again!

[frequencycentral]

I made my first 'drum synth' out of a white noise generator, a metal tin lid and a knitting needle when I was a teenager. The lid and needle were wired to 'complete' the circuit (like a switch - very Kraftwerk) and worked like a momentary power switch. I used a rotary switch with different size capacitors to define the release - the cap charged/discharged when the drum was hit. The bigger the cap, the longer the release as the cap was providing a little juice to the circuit after the lid/needle power switch was off. Completely mad.

Is this similar to what you are trying to do?

[Heemis]

Yes, you hit the nail on the head.  I'm currently thinking up a super lo fi analog drum machine.

Basically I want to have 2 independent oscillators, and a white noise source.  The "snare" will be a combination of white noise and 1 osc, while the "Kick" will be the other osc.  I'm still in the testing phase, but right now that's exactly how I'm triggering the "snare", using a momentary switch to complete the circuit.  This decay circuitry is exactly what I'm looking for.

When it's finished, I'm hoping to also build in an 8-step sequencer with 8 selectable switches to determine which part (kick or snare) is played on each beat.  This is in addition to individual triggers for each.  It's currently just a work in progress in my brain, but I'm pretty determined to see it through to reality.

[Mark Hammer]

Go here: http://mypeoplepc.com/members/scottnoanh/birthofasynth/id23.html

[Heemis]

Wow, this is super helpful, thanks for the link!

[oskar]

Yes, you hit the nail on the head.  I'm currently thinking up a super lo fi analog drum machine.

Basically I want to have 2 independent oscillators, and a white noise source.  The "snare" will be a combination of white noise and 1 osc, while the "Kick" will be the other osc.  I'm still in the testing phase, but right now that's exactly how I'm triggering the "snare", using a momentary switch to complete the circuit.  This decay circuitry is exactly what I'm looking for.

When it's finished, I'm hoping to also build in an 8-step sequencer with 8 selectable switches to determine which part (kick or snare) is played on each beat.  This is in addition to individual triggers for each.  It's currently just a work in progress in my brain, but I'm pretty determined to see it through to reality.

This looks like a match. The sequenser part could need an overhaul though and I think the digital switches and LFO's are supposed to be 4011's.
I started coding for a microprocessor drummachine like this but got stuck and later the harddisk went down, big time so all work got lost but I might get around to complete it someday.
http://www.synthdiy.com/show/?id=363