Saw PWM

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LektroiD
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Saw PWM

Post by LektroiD »

A conversation came up last week regarding the Alpha Juno "hoover" sound, which made me wonder if there are any oscillator projects out there which feature pulse width on the saw, like the Juno 1/2?

Seems every oscillator build I have encountered seems to only feature pulse width on the square wave, but not the saw. Is this possible in the analogue domain?
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jgb
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Post by jgb »

Image

Like the saw in the picture? Take a normal sawtooth waveform, patch through a VCA modulated by a pulse with PWM. The pulse should be some octaves above the saw.
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jgb
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Post by jgb »

Otherwise PWM on a sawtooth is to me more like modulating the shape of the waveform, from triangle to sawtooth and back, whereas the Juno is more like chopping it up.
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designator
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Post by designator »

If you want an animated saw wave you could try to add a saw wave and an inverted PWM wave from the same oscillator for example with an attenuverter. The resulting waveform looks like two slightly detuned mixed saw waves. This is not exactly PWM on saw waves but sounds good and is easy to try. In fact this how so called wave-multipliers work.
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flo
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Post by flo »

Wow some nice tips in here, gotta try to patch up some things.

Just wanted to add that the Cwejman VCO6 has saw PWM, which is very nice on it...
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windspirit
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Post by windspirit »

this is blowing my mind
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vtl5c3
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Post by vtl5c3 »

The Electronotes 129 VCO had SRM.

Check out page 5 of this PDF:

http://electronotes.netfirms.com/EN129.pdf
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Post by Piedwagtail »

Magnus Danielson's Sawtooth Phase Shifter.

http://rubidium.dyndns.org/~magnus/synt ... shift2.pdf
The U1A op-amp acts like a comparator providing a variable PWM pulse. The PWM pulse will counteract the initial sawtooth reset jump and insert a new reset jump. The position of the new reset jump is the result of the phase of the sawtooth (and thus voltage) and the phase CV signal. The comparator will flipp as the sawtooth raises above the CV input. The resulting sawtooth will have an error voltage which rises with the CV input, so this is compensated by hooking R4 to the CV input rather than the ground. The resulting sawtooth require amplification in order to resume the same swing as the input signal, this is provided by U1B, R3 and R4).

Part count: 1 double op-amp and 4 resistors.
I built and tested this; works!
On the scope, looks a lot like PWM.
Not as strong an audio effect from my tests but with a few oscillators maybe it sounds more substantial;
I'm including it in my present VCO build.


Robert
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Post by pre55ure »

I'm going to throw out an endorsment for the barton waveform animator. Not exactly saw wave PWM but it's the best "Hoover" style sound I've gotten from my modular. And its a quick and easy build. :party:
JohnLRice

Re: Saw PWM

Post by JohnLRice »

LektroiD wrote:Seems every oscillator build I have encountered seems to only feature pulse width on the square wave, but not the saw.
Just to be clear and FWIW, a square wave is a pulse wave with a 50% pulse width, 50% positive and 50% negative duty cycle.

For that Alpha Juno super saw sound you want a 'saw animator'. Do a search on that and you'll find references to modules like Cyndustries Saw Animator, Synth Tech E340 (a VCO that has saw animation/swarming built in) and Happy Nerding Super Sawtor etc.

I don't know of any DIY circuits out there that have saw animation built in but there may be since it seems like a good idea! :waah:
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Post by ben_hex »

pre55ure wrote:I'm going to throw out an endorsment for the barton waveform animator. Not exactly saw wave PWM but it's the best "Hoover" style sound I've gotten from my modular. And its a quick and easy build. :party:
Yeah the Barton animator is very good!
All DivKid video series to be found here!
http://www.youtube.com/divkidvideo
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LeftyLogic
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Post by LeftyLogic »

I'm actually in the middle of designing a VCO that has a sort of PWM-esque effect applied to the saw wave. It's similar to the type of skewable sawtooth that can be morphed between a downward facing ramp-to a triangle-to an upwards facing ramp, but instead of simply moving the peak back and forth, mine does this weird wavefolder-ish thing that has a really interesting sound to it.

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Graham Hinton
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Re: Saw PWM

Post by Graham Hinton »

LektroiD wrote:Seems every oscillator build I have encountered seems to only feature pulse width on the square wave, but not the saw. Is this possible in the analogue domain?
It is easy if you have a linear multiplier that is DC coupled. Here is how to implement it on a ModMix, which has two multipliers:

Image

The technique is to multiply a Pulse with other waveform(s) from the VCO and then modulate the Pulse Width.

A Triangle multiplied by a synchronous square gives a Sawtooth an octave higher.
A Sawtooth multiplied by a variable Pulse gives a Sawtooth that varies to a Ramp through a Triangle at 50%, similar to, but not the same as, EMS wave shaping.
Best results with a Pulse that goes from 0 to 100%.

The technique may be extended with another VCO at a higher multiple frequency being hard synchronised to the first. If you have a half wave rectifier the waveforms pictured above can be made too by multiplying with a pulse that goes from 0 to +ve instead of +ve to -ve.
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Re: Saw PWM

Post by DickyKnee »

Graham Hinton wrote: A Sawtooth multiplied by a variable Pulse gives a Sawtooth that varies to a Ramp through a Triangle at 50%, similar to, but not the same as, EMS wave shaping.
Best results with a Pulse that goes from 0 to 100%.
then mix in a DC/CV offset to make things more interesting.
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Graham Hinton
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Post by Graham Hinton »

... like this:

[video][/video]

[video][/video]


If you can't see these embedded videos they are also at:
http://www.hinton-instruments.co.uk/paprod/modular/modmix/moreapplications.htm
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