MSG822
From:  John Papiewski
Date:  Sun Oct 7, 2001  4:56 am
Subject:  SSG hijinx pt. 1 (longish)

Well, some of the recent message here have prompted me to look at the SSG with a little more detail.

The SSG is of course the Smooth and Stepped Generator module. It consists of two sub-modules, the top being the Smooth section, the bottom is the Stepped section. The outputs are tied together with a comparator at the CUPL. jack - this gives a HIGH if the smooth output is greater and a LOW if it isn't. *** CAUTION *** HIGH at CUPL is ~ 10VDC, LOW is ~ -10VDC. This is fine for use as a trigger but be careful when using it as a control voltage.... you won't hurt the Serge but if you're using it to control a VCA for example you may destroy your speakers and bring plaster raining down on your head from shattered walls.

The Smooth section is a VC lag processor with some interesting additions:

1. Hold input. When this goes high the output no longer tracks the input but is held at the same level that was present when Hold went high.
2. Cycle. This is similar to GATE on the DSG but not the same thing. It is normally not HIGH but LOW (-10V) The Rate knob determines the rate of lag. At zero rotation the *rate* is low, so that translates to a lot of lag.

The Stepped section is a sample-and-hold, also with interesting additions:

1. A rate knob. This determines how big each step is at the Stepped output. Full rotation = big steps, zero rotation = very tiny steps.
2. Cycle jack. This is also normally LOW (-10V). More on this in another installment.

The stepped section can serve as an extremely high quality sample-and-hold --- MOTM's sample and hold claims a droop rate of about 1mv per second - in other words, if you do a single sample driving a VCO at 1 volt per octave, then hold it and just listen without resampling you should be able to hear a VCO's tone drop perceptibly, without any trouble.
An informal test I did measured > 10mv droop in 400 seconds on the SSG. Other listening tests bear this out.

 

First, some simple SSG applications:

1. Linear Glide
   Patch the output of a sequencer or some other stepwise DC source into the Smooth input, then patch the Smooth output to an oscillator. See how turning the Rate control varies how fast the glide goes. Technical note: in this application the glide has a linear slope so you will hear a constant gliding rate from the oscillator (for a given Rate setting the volts/second gliding thru will be constant, it won't be faster or slower at the beginning or the end of the glide). In other words, perfectly nice and even.
   
   
2. Exponential Glide
   Same patch as above, but now also run a short patch cord between Smooth out and its VC Rate jack. Turn the VC rate knob clockwise so the control voltage is affecting the Rate to some degree. Now the glide should speed up at the end, depending on the position of the VC rate knob.
   
   
3. VC LFO (triangle) or VCO
   Run a short patch cord from IN to CYCLE. You should see the LED go from dim to bright to dim in a nice smooth progression.
   Patch SMOOTH OUT into a PCO or NTO and hear the pitch rise and fall. Vary Rate to make it faster or slower. Use VC Rate jack & knob to make the frequency voltage controlled.
   Patch SMOOTH OUT into your audio output path, whatever it is. You can use SMOOTH as a low-end audio VCO. Note that tracking & stability are NOT as good as PCO, NTO or DSG in this application, but it does give you an extra audio oscillator in a pinch. This is a triangle wave.
   
   
4. VC LFO (square) or CLOCK or VCO
   Same basic patch as #3. Instead of taking the signal from SMOOTH OUT, mult a banana plug into the patch cord connecting IN and CYCLE. This is a square wave that jumps from +10VDC to -10VDC approximately. As in #3 you can use this as an LFO for control voltage applications or as an audio square wave. Additionally it can be used to clock a sequencer or other module that needs a trigger or clock source.
   Note: if you use it as a trigger for the Stepped module it creates two triggers for every cycle. I don't know why exactly but this is what I've observed. As in #3 you can vary the frequency with a control voltage.
   
   
5. Lowpass Filter/Lowpass Gate
   Same patch as #1. Instead of patching a DC control voltage into the input, patch an audio source in, say, any PCO waveform. Send SMOOTH OUT to your audio output path. Notice that the sound is more or less intact at 100% rotation of the Rate knob, and as you turn Rate counterclockwise the harmonics and harshness get filtered and Smoothed out. Keep turning Rate counterclockwise, the sound will disappear altogether. So you can use this to filter harsh harmonics out of audio, or to create an unusual filtered effect. Use the VC rate knob and jack to make this filtering effect voltage controllable.
   You can employ this effect to create an audio Gate. What's a Gate? A gate is a general name for a device that lets you either permit or close off an audio signal. That's usually what you use a VCA for, and VCA's are very high quality examples of gates. You can use this patch, especially under Voltage Control, as an unusual substitute VCA: First, set the Rate knob at around 10 o'clock to 12 o'clock, just so your audio is no longer audible at the output. Now send a note envelope from DSG, DTG, or Envelope Generator to the VC rate jack, with the VC rate knob turned sufficiently high. You are creating low quality unusual envelopes where the harmonics are varying with amplitude. Using harmonic rich input, you have an unusual effect. Using purer input such as sine or triangle wave yields a more usual or typical result.
   
   
6. Sample and Hold
   Now we'll use the Smooth section to create a sample and hold effect! Send a varying signal from LFO or Random Source into Smooth In. Using a DSG or DTG create a rectangular clock pulse with a 99% duty cycle, that is, mostly 'on,' with a tiny 'off' part. Send that pulse into Smooth HOLD. Turn Smooth Rate fully clockwise. Send Smooth Out to a VCO or some other module that needs a control voltage. Play with the DSG rise/fall times and Smooth Rate. While HOLD is low the Smooth section takes a 'sample', when HOLD is high that sample is held.

This should be enough to get you going for a while!
More will follow later.

John P.

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Message 832
From:  John Papiewski
Date:  Wed Oct 24, 2001  3:39 am
Subject:  SSG hijinx part 2 ... long

Here's a few more things from the SSG trick bag:

First, a correction to the coupler thing! The COUPLER goes HIGH if the STEPPED OUT voltage is greater than SMOOTHOUT. The catalog sheds no light on this but that's what my measurements say.

1. Pointy wave generator
   Patch CYCLE to IN on the Smooth generator, then also patch SMOOTH OUT to VC RATE. Mult another banana into SMOOTH OUT and use it for CV or audio. Instead of generating triangle waves with linear sides you're making exponential pointy waves. Vary RATE and VC RATE for different effects.
   
   
2. Straightforward Sample-and-Hold, periodic.
   Send the output of any oscillator or LFO to the Stepped section's IN jack. Patch up a clock using a DSG and send its trigger pulse to the SAMPLE jack. Turn the Stepped RATE knob fully clockwise. Patch STEPPEDOUT into the CV input of an audio oscillator. Watch how the the STEPPEDOUT LED flashes brighter and dimmer in time with the clock pulse. Note how the combination of clock pulse rate and LFO frequency affects the stream of voltages coming out of Stepped.
   
   
3. Straightforward Sample-and-Hold, random
   Use the setup in #2 but instead of using an oscillator or LFO to feed the IN jack, use a noise source or S/H SOURCE. Now no matter how fast or slow you run your DSG clock, you will have random pitches coming out of your audio VCO.
   
   
4. Squashed Sample-and-Hold
   Use the setup for #2 or #3, vary the Stepped section's RATE knob. Note that as you turn the knob counterclockwise the amount of each step becomes less and less. The RATE knob slew-limits how fast the sample-and-hold can change. Given enough time the maximum high and low points will still be hit but each step will be more modest. At fullcounterclockwise rotation step size is inaudible - I can't hear it, can you? At settings over 50% you can get interesting subtle ultra-microtonal variations.
   
   
5. Loony Tunes & Merry Melodies (™ AOL-TIME-WARNER ;-)
   Patches #2 & #3 are perfect input for a quantizer if you have one. Note that in setup #2 you have interesting repeating patterns but the patterns inevitably have some kind of drift, unless you know the clock and the LFO are sync'd together somehow. A quantizer won't eliminate the drift but will turn it into something melodic. Patch #3 is fun using a quantizer also, but instead of producing pretty repeating patterns you'll get crazy notes all over the place.
   
   
6. Autoerotic Sample-and-Hold.
   Well, since you can patch the Smooth section as a square wave pulsegenerator, you can use that pulse to trigger the SAMPLE input of the Stepped side. Strangely though, for every cycle of the square wave you get TWO evenly spaced triggers... so the clock rate for the Smooth pulsegenerator is doubled if it's used as an S/H trigger.
   
   
7. Zero-crossing detector.
   Noting that the COUPLER output goes high if STEPPED OUT is greater than SMOOTH OUT, you can use this as a simple spare comparator. Patch any AC coupled signal into Smooth IN and take the COUPLER out to trigger or do something... every time Smooth IN goes NEGATIVE, if nothing's going into Stepped IN and Stepped's essentially unused, that satisfies the condition of Stepped being GREATER, and the COUPLER goes HIGH...again
   PLEASE NOTE that due to the wide voltage swing of the COUPLER output,take great care using it for audio and CV applications! Note also, you don't need to send SMOOTH OUT or STEPPED OUT anywhere in this application.
   
   
8. Up/Down staircase generator.
   Patch Stepped's CYCLE to IN. Note that, unlike doing this with a DSG orthe Smooth section, you're not getting a repeating cycle. Now send aclock pulse to SAMPLE. Turn the RATE knob fully clockwise. You can patch STEPPED OUT to your audio VCO again. It will be a somewhat jerky rising and falling staircase, a staircase that rises stepwise to a maximum then falls stepwise to a minimum. Now rotate RATE counterclockwise... you will hear the number of steps per cycle increase, and the size of each step decrease proportionately. So you'll be hearing lots of itty bitty steps rising to a peak, then falling off to a minimum. Very cute. At full counterclockwise rotation of RATE the steps will be inaudibly tiny... it will simply sound like a smooth rising and falling like a nice smooth sided triangle LFO. Now vary the clock rate going into SAMPLE and see how that changes the output. The size of the steps of the staircase depends on RATE, and the speed of the steps depends on the clock going into SAMPLE.
   
   

Well, taking the 6 applications in the first installment with the 8 in this one brings us to 14 applications of the SSG - that is, ONE TWO-PART SERGE MODULE.
Just think about that for a minute.
Now please consider that these are fairly BASIC SSG applications. For the next installment, I will get into some more advanced stuff...

Till then, peace to all
John P.

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Message 833
From:  John Papiewski
Date:  Mon Oct 29, 2001  5:02 am
Subject:  SSG hijinx pt 3

The Random Source

In this installment I'll cover a more advanced application of the legendary Serge Smooth & Stepped Generator.
The Serge catalog entry for the SSG describes the coupler section as being related to another module, the Random Source (RS)... that the RS is in fact a Noise Source internally hooked to an SSG... and that the SSG can be patched up as a Random Voltage Generator... but tantalyzingly and oh-so-typically of Serge (and Buchla, I think) to not say how it's done... at least not in the catalog.

So what the SSG does is somehow take a random signal and deliver the Random Source's random pulses, random stepped and random smooth signals. Doing this is a very handy thing for Blue Funstation owners, or anyone who happens to have a Random Source and an SSG... and has a desire for multiple uncorrelated random signals --- in other words, a slow random smooth voltage controlling one vco, a rapid stepped random voltage controlling another one at the same time. Or other combinations.

First off, an SSG can't be used as a Random Voltage Generator all by itself, it needs a random signal to feed it. You need the S/H source of a Serge Noise Source or Random Source.

Patch it into the IN jack of the Stepped side of the SSG.
Now patch the COUPLER to SAMPLE of the Stepped side, mult another patch cord into COUPLER, and patch it into the IN jack of the Smooth side. That's it.

The Smooth random voltages are available at SMOOTH OUT, the stepped ones are at STEPPED OUT, and random pulses are available at the COUPLER (which is also patched to SAMPLE and Smooth IN).

With the Stepped RATE knob at full, varying the RATE knob of the Stepped side changes the rate of BOTH the Smooth and Stepped random voltages. This exactly what the Random Source has. Varying the RATE of the Stepped side changes the amplitude of your Smooth and Stepped randomvoltages... so turning the Stepped RATE knob down reduces the amplitude of the signal at the OUT jacks. Of course, the Smooth RATE and the Stepped RATE can be voltage-controlled via their respective VC RATE jacks & controls too.

The fun doesn't stop here though... see what happens if, instead of using the S/H source to feed the SSG, you use an oscillator, or a DSG, or a sequencer...

Have fun!
John P.

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Message 3060
From:  Bob Hearn
Date:  Thu Nov 4, 2004  5:17 am
Subject:  Re: [SergeModular] Re: Smooth Stepped Cycle Jacks?

On Nov 3, 2004, at 11:10 AM, Fernando wrote:
> A month or so ago I spent some time really grokking the SSG.
> I think I was able to completely satisfy myself on every point about its
> behavior, even answering some unresolved questions from SMOG.
> The module really does make sense; all of its apparent strangeness can be explained.
> Please Bob, it would be a pleasure to read an extensive report!
> Fernando

John's SSG posts that you mentioned pretty much constitute the definitive application survey, I think. I didn't find them until after I had done my experimentation. I do have a few things to add to his reports, more about functionality than applications.

Some of this I mentioned before:

1. The Stepped section is really just like the Smooth section (which is a VC lag processor), with some extra input circuitry. The differences are that (1) the slew rate for a given RATE knob setting and VC input is much faster, and (2) the SAMPLE input works as follows: it detects rising edges (but see below), turns them into fixed (very short) duration pulses, then inverts that signal to effectively feed into an internal HOLD input (as on the smooth section). So the Stepped section is normally in a hold state; you release it and let it slew very quickly for a very short duration with a trigger pulse - effectively, this steps it by an amount depending on the RATE knob and VC. The slewing is clear looking at the signals on an oscilloscope.

2. John noted that if you patch the Smooth CYCLE output to Stepped SAMPLE, you get two sample steps per Smooth oscillation period. I also don't know exactly why this is, but there is nothing special about the fact that the signal is coming from CYCLE. Evidently Stepped SAMPLE detects not only rising edges, but also falling edges with a ~20v drop, which is what CYCLE generates when it goes from +10v to -10v. It is rather tricky to generate such a signal externally (processors are nonlinear when the voltages get large, and don't fully add their inputs), but it can be done, and Stepped SAMPLE again triggers on the falling edges as well as the rising ones. This doesn't happen with normal, 5v to 0v falling edges. Also, it's something peculiar to the Stepped module; no other rising edge detectors I've tried (e.g. DSG, sequencer clock) trigger on CYCLE falling edges. Presumably the behavior has to do with the fact that the edges are being turned into short pulses.

3. John also noted that CYCLE is normally low (on both Smooth and Stepped). This is simply because it only goes high when OUTPUT goes below about -1v (on my system, anyway). It goes low again when OUTPUT goes above about 4v.

4. Beware the SSG diagrams in the Gold book, which mistakenly draw CYCLE as an input - it is an output.

5. I thought I'd seen other posts puzzling over some CYCLE weirdness, but I can't seem to dig them up at the moment. One thing that puzzled me for a while was this: if you feed a square wave into Smooth INPUT, and crank the RATE up enough to get triangle waves, CYCLE just sits at -10v. But if you patch CYCLE to INPUT, it alternates between -10v and 10v. It's like CYCLE somehow alters its behavior based on the fact that it's patched within the SSG. But the answer is simply given by #3 above - an ordinary square wave does not go below 0v, but CYCLE does. There's really nothing weird about CYCLE.

6. You can make a Random Voltage Generator even without a Noise Source!
John described how to turn the SSG into an RVG, with smooth, stepped, and pulse random voltage outputs. This is also described in the Gold book (page 5-39).
This is an incredibly cool patch - if you fully understand it, you have got the SSG down.
However, one thing is that that patch requires the S/H source from a Noise Source module (or a Random Source, which includes a Noise Source internally). That signal is a randomly modulated sawtooth wave. The idea is that every time you sample it (unless two sequential times are very close together), you get a random voltage. (Actually the Gold book mistakenly says to use the S/H output, not S/H source - that will not work.)
Well, it turns out you can make an RVG even without a Noise Source! Just use a regular sawtooth wave instead of the S/H source, say from a PCO. (A DSG would also work.) Set the PCO to high range, with the frequency knob at 12 'clock. Now, this signal is not randomly modulated, so you might think it would not work - you won't get a random voltage when you sample it. But in fact, the overall system is chaotic; the samples you get are actually random, because they are sampled at random intervals - because the patch in fact works! It's circular - the samples are random, because the patch output voltages are random, because the samples are random... but it works. I haven't done the hairy math to ensure that the system will never get locked into a repeating state, but the output looks the same to me as an actual RVG.
In dynamical terms, I believe the cyclic states are unstable. Note that if the sawtooth PCO rate is much faster than 12 o'clock, the patch doesn't work - I think because the signal is changing too fast for the Stepped section to lock onto. This makes sense given #1 above; the Stepped module is actually slewing for a brief period, and not actually sampling. Setting the PCO rate to 12 o'clock roughly matches the S/H source signal's mean frequency, btw. Of course, this is really only useful if you happen to have an SSG but no Noise Source... still, I think it's cool that you can get your randomness for free, as it were.

Bob Hearn

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Message 3061
From:  Bob Hearn
Date:  Thu Nov 4, 2004  6:23 am
Subject:  Re: [SergeModular] Re: Smooth Stepped Cycle Jacks?

A short addendum to my previous post...

> 2.John noted that if you patch the Smooth CYCLE output to Stepped SAMPLE,
> you get two sample steps per Smooth oscillation period...
> Evidently Stepped SAMPLE detects not only rising edges, but also falling
> edges with a ~20v drop, which is what CYCLE generates when it goes from +10v to -10v.

I just realized this is a feature, not a bug.
If Stepped SAMPLE didn't trigger on 20v falling edges, the Random Voltage Generator would not work, because a new random voltage would not get sampled when the rising Smooth output reached the sampled voltage (causing CUPL, which is patched to SAMPLE, to go from 10v to -10v).
So I think we can assume that Stepped SAMPLE was simply designed to fire on large falling edges, so that the RVG patch would work, and not on small falling edges, so that ordinary pulses give the expected behavior.

Mystery solved!
Bob