Penfold Dynamic Tremolo

StephenGiles · March 18, 2006, 04:13:02 PM

Oh , it just went to a VCF. I forgot to erase it on the envelope follower section. If you open it in Paint, use the erase tool to get rid of that rogue line!

calpolyengineer · March 18, 2006, 08:27:07 PM

oh, ok. Thanks.

-Joe

RaceDriver205 · April 03, 2006, 01:10:48 AM

Hows your design going then?

calpolyengineer · April 03, 2006, 01:23:24 PM

It has unfortunately taken a sabbatical while I get my schooling in order. I think I have the schematic done, I'm working right now on getting it into PSpice to test it and making a PCB layout. Hopefully I'll get to start going on it pretty soon. Thanks for asking though.

-Joe

Dave_B · April 03, 2006, 01:35:39 PM

Wouldn't this be a good candidate for a µC project?

If I could get my wife to take the kids out of town for a few days and quit my band I'd do it. $:-\$

calpolyengineer · April 03, 2006, 01:53:42 PM

uC certainly is not my forte. I wouldn't even know where to begin.

-Joe

RaceDriver205 · April 24, 2006, 03:29:16 AM

Come on calpoly, I want to build it!

Mark Hammer · April 24, 2006, 09:13:03 AM

My own prejudice in the matter is that the sort of envelope following or envelope generation that works well for filters will likely be unsuitable for dynamic tremolos. The reasoning is that the filter parameters are supposed to affect the note at an individual level, whereas dynamic tremolo - unless it is intended to deliver a sort of quasi-ring-modulated trill at the start of a note - is supposed to map onto phrases and clusters of notes/strums. As such, what one needs is something that averages out multiple peaks (as Stephen initially implied with his suggestion to use the pluck follower), and introduces more lag, and perhaps a different sort of decay, than a normal HWR or FWR would provide.

calpolyengineer · April 25, 2006, 04:02:37 AM

Ok I'm back on working this thing out. I just have one question, do you think variable duty cycle is a useful feature of a trem? I'm asking because that is one of the selling points of Smallbear's 555 tremolo that I could use as a starting ground for this. Also, I don't think I will make it a true envelope controlled, just a triggered envelope generator with a variable initial, final, and sweep speeds.

gez · April 25, 2006, 04:46:52 AM

Quote from: calpolyengineer on April 25, 2006, 04:02:37 AMAlso, I don't think I will make it a true envelope controlled, just a triggered envelope generator with a variable initial, final, and sweep speeds.

I've found triggered LFOs to be of more use than voltage controlled LFOs in tremolos. Only problem is that the trem gets 'gated', ie cuts out, towards the tail end of notes. One way round this might be to use a re-triggerable monostable so that when the signal drops below the threshold where it would normally cut out, the mono keeps things going for a short period of time...tricky balancing act though!

Either that or figure a way of making the depth fade out as a note decays (I think that might be more musical actually).

RaceDriver205 · April 25, 2006, 04:55:26 AM

As far as I know duty cycle is only for square waves. Square waves make tremolos too choppy and makes them less pleasant, so you have to filter the square wave well to make them more sine-wave like. I have a perfect-sine-wave tremolo and it is very pleasant. Having a variable duty cycle filtered square wave sounds interesting - I have never heard of this feature in a tremolo before and I dont know if it will make the tremolo better.
Glad your back into it!

calpolyengineer · April 25, 2006, 04:59:42 AM

But couldn't you just use an integrator to make it a triangle wave, then another integrator to make it a pseudo-sine wave? That is what I was intending to do. Then using this, you could even have a ramp up or ramp down by using the triangle output with the duty cycle all the way up or down, and a "rectified" sine wave type tremolo which I haven't even heard of before and seems to be interesting.

Quote from: gez on April 25, 2006, 04:46:52 AM
the trem gets 'gated', ie cuts out, towards the tail end of notes

I don't quite follow. Isn't the use of the triggered LFO to eliminate the gating at the tail end of the threshold? I do agree that it needs to be retriggerable though. I also like that depth idea.

-Joe

gez · April 25, 2006, 05:59:32 AM

Quote from: calpolyengineer on April 25, 2006, 04:59:42 AM
But couldn't you just use an integrator to make it a triangle wave, then another integrator to make it a pseudo-sine wave? That is what I was intending to do. Then using this, you could even have a ramp up or ramp down by using the triangle output with the duty cycle all the way up or down, and a "rectified" sine wave type tremolo which I haven't even heard of before and seems to be interesting.

In the standard 2 amp triangle LFOs, varying duty cycle varies the slope of the triangle, which ultimately can give you a sawtooth. With a further integrator you get a sinusoidal wave form and varying duty cycle gives you a 'swing feel'. Edit: though I suppose at extreems you'd get something akin to a rectified sine.

I have actually tried FW rectified sinewaves in trem circuits and they're not that good. With +ve going it sounds as though there's no depth as the attenuation happens for a shorter period than it would with a full-blown sine. With -ve going - if my memory serves me well (been a while) - it's the reverse (sounds a muddy mess)

Quote from: calpolyengineer on April 25, 2006, 04:59:42 AM
Quote from: gez on April 25, 2006, 04:46:52 AM
the trem gets 'gated', ie cuts out, towards the tail end of notes

I don't quite follow. Isn't the use of the triggered LFO to eliminate the gating at the tail end of the threshold? I do agree that it needs to be retriggerable though. I also like that depth idea.

In my books a triggered LFO is one which is synched to the initial attack of a note/chord. As amplitude of the signal goes down there'll come a point where the 'on switch' is tripped and the LFO cuts out.

calpolyengineer · April 25, 2006, 07:05:34 AM

Oh, yes. I see. I thought you were talking about the instability that would arise if the rate were directly controlled by the envelope. Yes there would be that gating in a triggered LFO, that is unless the LFO were designed not to have false triggers (Mark Hammer's website has a Craig Anderton article about one such LFO) which I can hopefully utilize in my project. The Anderton one also has a great retrigger setup so that subsequent real triggers will start the LFO at the beginning rather than at the last position of the LFO from the previous triggered sweep. Sorry for the confusion by the way.

-Joe

gez · April 25, 2006, 07:17:58 AM

Quote from: calpolyengineer on April 25, 2006, 07:05:34 AM
Yes there would be that gating in a triggered LFO, that is unless the LFO were designed not to have false triggers.

If you design the envelope follower well there shouldn't really be much of a problem with false triggers, but there will definitely have to be a cut-off point where the LFO is meant to turn off otherwise it'll be 'free-wheeling' and won't be synched to the initial attack of the signal to be tremoloed (as I type I wonder how the spell check will deal with that one!).

QuoteThe Anderton one also has a great retrigger setup so that subsequent real triggers will start the LFO at the beginning rather than at the last position of the LFO from the previous triggered sweep. Sorry for the confusion by the way.

That's the way most (all?) analogue set-ups work...or at least how most circuits are set up to work - when there's no signal the LFO is off and when you start playing the LFO starts from scratch to the initial attack of the signal. I think it would only be digital/pic that would be able to start up where it left off.

gez · April 25, 2006, 07:46:49 AM

Hmmm, might be a way to have a free-wheeler that resets itself with strong attacks. I'll have to check out those schemos you mentioned.

RaceDriver205 · May 05, 2006, 08:23:24 AM

Hows it going Capoly?
(I know, I know, im a nag!

)

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Penfold Dynamic Tremolo