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 Forum index » DIY Hardware and Software
pulse to Complex Waveform generator
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zipzap



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PostPosted: Tue Jan 17, 2006 7:30 am    Post subject: pulse to Complex Waveform generator Reply with quote  Mark this post and the followings unread

Hi there
Some of the nastiest sounds i ever heard ocured when i was clocking my 4017 sequencer at audio speed, using the output as sound sorce.
The shemati is an idea i had that should make it possible to use the pulse output of a vco and use the pulsewidth, transfering it to the new waveform.
1 The diode eliminates the negative part of the pw
2 the uper r-c-buffer reacts on the pulse going up, the lower with the inverter reacts to the pw going low. the resulting short pulses are added and cklock the 4017.
I´m not sure about the values for r and c, i guess a much shorter pulse with eg. 50n/10k would be better to get a decent clocking signal and to assure that the two parts dont overlap. What do you think?
3 The rest is standard 4017 sequencer, maybe variable step length, and the output glide (very effective on harmonics), offset, level, buffer.
The frequency of the waveform will be linked to the vco, but it can be varied depending howmany steps form one cycle.
When i will build this i want to use faders instead of pots, so you can see the waveform you´re drawing.
Of course this circuit can be used as a modulation sequencer at lower clock speed also.
By the way, if i want independant rise and fall glide, do i use 2 Diodes an 2 pots so the cab is charged and discharged over different resistors?


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Scott Stites
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PostPosted: Tue Jan 17, 2006 9:07 am    Post subject: Reply with quote  Mark this post and the followings unread

Looks like it would work. To avoid general glitchiness, I usually try to square up anything that's going to be clocking CMOS.

An alternative plan would be to use a dual comparator and an EXOR gate. One section of the comparator could be used to square up the input from the VCO after you've chopped off the lower section of the waveform with the diode (it could even respond to VCO waveforms other than pulse). This signal one could send to one input of the EXOR gate.

After that, the second comparator would be used to square up a delayed signal that's applied to the second input of the EXOR - this would double your frequency. The EXOR would pulse when the input went high and pulse when the input went low.

This circuit would run like a bat out of hell:

http://www.maxim-ic.com/appnotes.cfm/appnote_number/3327

The output is inverted from the clock in. If that's a problem, one could always use another section of the EXOR IC to flip it back to the polarity you want.

In lieu of the MAX9010, an LM358 would work wonders. For the EXOR, use a CD4070. A CD4030 would work as well, but check PS ratings.

For a good working app on the LM358, check out Ken Stone's Pulse Divider:

http://www.cgs.synth.net/modules/cgs36_pulse_divider.html

Of course, you could just use an EXOR with one leg having an RC delay and drop the comparators, but it would probably run better and faster with them.

Lag - here's an example from the inestimable Harry Bissell. Bonus 'shape' feature to fade between linear and expo response (oftentimes I prefer linear response for keyboards, I suppose it might give you some variation for sequencer out as well).

Cheers,
Scott


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Harry Bissell's Morph-Lag Design
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mosc
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PostPosted: Tue Jan 17, 2006 1:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

What does R2 do in Harry's circuit? Seems to me like it shouldn't be there...
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Scott Stites
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PostPosted: Tue Jan 17, 2006 2:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

Summing resistor for AR3? Wouldn't it put inverted CV out at virtual ground if it were not there?
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PostPosted: Tue Jan 17, 2006 2:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK, I don't get it though. I'm sure it works but I've never done lag processors like this myself.
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Scott Stites
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PostPosted: Tue Jan 17, 2006 2:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Right, I understand it's for summing - do you mean by the original question that one wouldn't want to sum the inverted signal with the input?
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PostPosted: Tue Jan 17, 2006 2:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

I guess that makes two of us. I've read build reports on it though - seems to work pretty well. I guess it's also handy for the other lag duties (shaping gates into envelopes, etc).

The only other lag I've ever used is a linear design, which warn't nothing like this (much simpler). Having the ability to move between the two responses would be a lot of fun. I guess I'll have to try it out!
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PostPosted: Wed Jan 18, 2006 7:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Maber that feedback has some effect on the operation. duh...

Yes, everything I've built has a linear response - just simple integrators really.

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PostPosted: Wed Jan 18, 2006 10:59 am    Post subject: Reply with quote  Mark this post and the followings unread

I haven't grokked what the shape pot is doing.

Not to hijack the thread but:

Here's a linear glide circuit I pulled out of the SDIY archive a few years back. Coincidentally, it's a circuit of Harry's as well. I remember contacting him and telling him how much I liked it - I recall him mentioning he saw it as a sub-circuit to some medical device and just tried it out. He was insistent on this design to use a 741 or 1458 or similar (I think latch-up was the concern?).

My keyboard is one I built from Tom Henry's "Build a Better Music Synthesizer" and has expo glide built into it (pretty much the standard pot and cap sandwiched between two buffers, without the feedback of this design). Though I use expo lag a lot because it's built into the keyboard, I found linear lag to be really, really sweet. One thing about Harry's design though, in retrospect, is that I think it could use a 100 ohm resistor in series before the 1M pot. Moving the pot from min resistance to any resistance at all would slightly change the tuning of a VCO controlled by the output, so I'd always have to retune if I shut the linear glide all the way off.

This newer design by Harry would be the best of both worlds, I think.

If anyone's wondering what this is all about, generally speaking, and IIRC, the glide time of linear glide is determined by how far the first note is from the second note - IE, gliding up 2 octaves would take longer than gliding up one octave.

Expo glide, on the other hand, will take the same amount of time gliding up two octaves as it takes to glide up one octave, so the farther apart the glide points are, the faster the glide will appear to move.

Linear glide to me is definitely a lot more 'expressive' when using it with a keyboard. Didn't the MiniMoog have linear glide?


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Harry Bissell linear lag circuit
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PostPosted: Wed Jan 18, 2006 11:18 am    Post subject: Reply with quote  Mark this post and the followings unread

That is a circuit I'm more familiar with. Very Happy
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PostPosted: Wed Jan 18, 2006 11:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Working at Buchla, I imagine you probably saw a few more exotic things than that, too Very Happy (I've tried the VC Integrator from the 266 SOU - I didn't have the same dual PNP, but used a 2SA798, which seemed to work 'OK').

This is the lag circuit I was most familiar with - works OK with keyboard, but I don't like it nearly as much as the linear circuit above for keyboard. This one works great with S&H and other general lag nuttiness.

Cheerio,
Scott


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PostPosted: Wed Jan 18, 2006 11:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Just one switch to go from one to the other... Very Happy
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ian-s



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PostPosted: Wed Jan 18, 2006 12:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Scott Stites wrote:
Didn't the MiniMoog have linear glide?


Yup, the rate varies a little over the range of the keyboard but I dont think this is a feature.

Going just from the description, expo sounds like it should be the best option. In practice though, it sucks.
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PostPosted: Wed Jan 18, 2006 1:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Yup, the rate varies a little over the range of the keyboard but I dont think this is a feature.

Going just from the description, expo sounds like it should be the best option. In practice though, it sucks.


Thanks for that - I've heard that the Moog modular had expo lag - is that the case?

Quote:
Just one switch to go from one to the other...


Yep, one switch. I've never looked into putting it on my keyboard - it's slightly more complicated (not much) because the buffer is a discrete FET buffer rather than an op amp buffer. That's not the hurdle. It's already soldered up on a board and my natural laziness has prevented me from actually *doing it*. That's the hurdle. Very Happy

The idea of a continuously variable fade from one response to the other to me is intriguing - don't know if that's one of those things that sound better on paper than it really is, though. There's not a lot to the circuit, though obviously there's more than a dual op amp buffer and a switch.

Take care,
Scott
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zipzap



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PostPosted: Thu Jan 19, 2006 4:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
An alternative plan would be to use a dual comparator and an EXOR gate. One section of the comparator could be used to square up the input from the VCO after you've chopped off the lower section of the waveform with the diode (it could even respond to VCO waveforms other than pulse

Do you think it could be possible to generate a pulsewave from an acoustic signal like a violin or guitar? I managed to trigger my sequencer with my bass, moving it one step each time i hit a note.
Would be great to have the complex waveform generator in tune with my bowed doublebass (just imagine that...)
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PostPosted: Thu Jan 19, 2006 10:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Absolutely! Check out the Wilson Signal to Gate thread.

You would have to adjust the threshold so that the signal produced a gate on the attack of your note, and go low again before the next note so it could then go high and trigger as well. Certainly doable!

Take care,
Scott
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