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 Forum index » DIY Hardware and Software
New plucked/damped envelope gen circuit (piano/clav+hihat)
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Ricko



Joined: Dec 25, 2007
Posts: 196
Location: Sydney, Australia
Audio files: 17

PostPosted: Sat Sep 15, 2018 5:03 am    Post subject: New plucked/damped envelope gen circuit (piano/clav+hihat) Reply with quote  Mark this post and the followings unread

I have been playing with the circuit on the simulator today. It is an envelope generator for struck/plucked instruments (things that will ring until they die down) such as piano/clav/bass/cymbal. Plus it has a "second mode" that can be switched in for effects like open/closed high-hats, damped guitar picking, or harpsichord's "lute" stop.

It features multiple kinds of damping: Release. Decay, Dampen pedal, Limiting, friction damping.

The final circuit is small but a little dense, so I will present it as a series of 3 circuits of increasing complexity. There is a tweaked version for hihat at the end, too, with an interesting "soft note erasor" knob.

Here is the first. This just takes a gate and produces a decaying tone. There is a Decay time control. (Because log decays take forever, there is a diode drop on the output: this simulates how real instructions usually don't decay with a long tail due to friction etc.*)

The signal goes from left to right. You can see in the design there is a transistor buffer, a monostable multivibrator to give a clean trigger, then the integrator and output buffer.

* If you want a gong sound, however, you probably want a long release, and might prefer no diode drop: but, to a great extent, long releases are better done using reverb units: the Envelope Generator can pay more attention to the envelope behaviour at the note on and note off.


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Last edited by Ricko on Mon Sep 17, 2018 7:59 am; edited 4 times in total
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Ricko



Joined: Dec 25, 2007
Posts: 196
Location: Sydney, Australia
Audio files: 17

PostPosted: Sat Sep 15, 2018 5:08 am    Post subject: #2 Release and Velocity On Reply with quote  Mark this post and the followings unread

This version adds a Release time, when you release the gate. The Release time is always faster than the Decay. (There is no Attack or Sustain needed for these kind of envelopes.)

This version also allows accents, through the velocity input. (This should held to 5V if nothing is plugged into the velocity circuit.) The velocity accent works by making the monostable's pulse louder, down to nothing. You can see the pulse following the velocity input in the chart next.

This version also has an op-amp as the last buffer, to help with offset control.


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Last edited by Ricko on Sun Sep 16, 2018 5:32 am; edited 5 times in total
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Ricko



Joined: Dec 25, 2007
Posts: 196
Location: Sydney, Australia
Audio files: 17

PostPosted: Sat Sep 15, 2018 5:19 am    Post subject: #3 Dampen and limiting Reply with quote  Mark this post and the followings unread

This version adds a Dampen input. (Actually it can be continuous for a different effect, but its main function is to be gated, e.g. by a footswitch or LFO.)

Dampen is rather like the lute stop of a clavichord or harpsichord, or the dampen pedal on a piano, or the "all note off" MIDI function, or grabbing a cymbal: if there is a new note, it makes it very short and softer, if there is an existing note ringing or held it kills it. (Opps, the gate is upside down...) In the circuit, has three little parts: an input buffer for the Dampen input signal), a dampen circuit to deplete the capacitor no different to the Release mechanism, and a little diode chain clipping circuit enabled with the dampen that makes it softer.

I have made a tweaked version below of this circuit as a HiHat Envelope Generator, where the Damp input acts as hihat open/close.

The limiter effect is based on the observation that when you hit a piano fff and ffff there is no real difference in maximum volume, as the strings cannot vibrate more than their nature, but instead the extra energy changes the envelope shape, to be fatter. (Supposedly, this flat top is what makes the Minimoog EGs "fat"). You can see the effect in the Out trace in the first second (of time), where there is a little "roof" visible.

If I get round to it, I could add legato/Hold2 (turn off the G signal) and NotOff velocity (add a negative gate to offset the signal after R30.) But this seems enough.


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Last edited by Ricko on Sun Sep 16, 2018 5:35 am; edited 6 times in total
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Ricko



Joined: Dec 25, 2007
Posts: 196
Location: Sydney, Australia
Audio files: 17

PostPosted: Sat Sep 15, 2018 7:02 am    Post subject: What is different about this EG? The velocity? Reply with quote  Mark this post and the followings unread

What is the point of another EG design? I guess the thing that makes this EG different from many is that I am trying to model the operation of energy being transferred to a resonating object. So this perhaps gives the velocity (and so on) a different action.

You can see in the figure below, when the same gate time and Decay setting is used, but the velocity is different, the high velocity envelope is not only louder but it takes almost 20 seconds to complete.

But when the velocity is low, it is not only softer, but it also only takes 5 seconds to complete. This is different from, for example, a velocity system that only amplifies the eg but maintains the same time constants. (You could get a similar effect by variable biasing and half rectifying, I guess.)


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Ricko



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Posts: 196
Location: Sydney, Australia
Audio files: 17

PostPosted: Sat Sep 15, 2018 9:18 pm    Post subject: Hihat circuit Reply with quote  Mark this post and the followings unread

So here is the struck/damped EG #3 tweaked for use as a hihat EG. Damp 0V is open and Damp 5V is closed, however, it does have a transition not just one or the other so you can use variable CVs not just a gated signal.

Apart from tweaked values, there are three new pots for performance tweaking:

1) The Closed pot gives the decay for when the Damp input is high. I.e. the sound of the closed hihat. This is always less than the open sound.

In the charts below you can see the difference between adjacent beats.

2) Increasing Fatness pot will thicken the strokes, and make the velocity effect slightly less. Vary this in real time for performance effect. (It works by varying the amplification of the offset signal to the limiter diode.)

In the charts below you can perhaps see an example in the hithat-99.jpg image,in the centre, where the beat is thicker than the comparable spot on other diagrams.

3) The Soft Note Eraser pot will usuallly be at 50%. But if you move it towards 0% it will start omitting envelopes when there is low velocity. Moving it towards 100% gives a more even kind of accenting where there are only two levels of accent (mid-low and mid high) depending on velocity. Varying this pot when playing a repeating beat sequence will result in rhythm and accent variation of that sequence. (It works by making the output pulse of the monostable too short on soft notes to charge the integrator capacitor.)

You can see this effect in the charts below: the hithat-50.jpg is the typical setting with maximum velocity variation and all notes playing. The hithat-00.jpg has a setting of 00 so when the velocity input is low the notes simply do not play. The hihat-99.jpb shows the two level accent affect of the eraser knob at 100%


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Last edited by Ricko on Sun Sep 16, 2018 5:41 am; edited 2 times in total
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Ricko



Joined: Dec 25, 2007
Posts: 196
Location: Sydney, Australia
Audio files: 17

PostPosted: Sat Sep 15, 2018 10:33 pm    Post subject: Phantom Beat Envelope Generator Reply with quote  Mark this post and the followings unread

This circuit builds on the HiHat circuit. It duplicates part of it.

By long tradition, drummers have a finite number of arms. But drummers bore easily, even in the gaps between playing notes. And if there is too long, it is easier to lose the beat. So drummers often play "phantom beats" or "ghost strokes" for the beats when they are not playing the main instrument: sometimes in the air, sometimes on a spare leg, but often on some other instrument, softer.

These phantom beats often form interesting rhythms in their own right, and can give the effect of multiple players.

In the HiHat Envelope Generator previously, I added the Soft Note Erasor feature, so that low velocity notes don't sound at all. So it is easy to take the same velocity circuit, invert it, and produce a second simple drum envelope only when the velocity is very low.

You can see the effect in the chart below. This is pretty much the same effect as "velocity switching", but applied to envelope generators. If the main envelope was for a hihat sound, the phantom envelope might be for a soft snare sound, for example.

The Phantom Beat generator could also be used for notes not just beats: one envelope drives the VCA for the m and ff notes and the other drives the VCA with some different waveforms for the pp notes, for example. Or to add variations to sequenced lines with Dampen driven by a LFO (reset every few bars) to switchover between the different sounds, as another example. Stretch your sequencer or trigger sequencer further!


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Last edited by Ricko on Sun Sep 16, 2018 5:51 am; edited 2 times in total
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g.gabba



Joined: Nov 29, 2008
Posts: 387
Location: berlin
Audio files: 23

PostPosted: Sun Sep 16, 2018 12:14 am    Post subject: Reply with quote  Mark this post and the followings unread

interesting as always,
but i need to read it two more times, at least

thx for sharing
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