Powwow 4 - Feedback

Here’s the recording of my live set at the fourth Berlin Powwow session which you can buy from my Bandcamp.



For this performance I wanted to explore feedback and the obstacles and modifiers one can place in the loop. The key players in this were delays, filters, non-linear functions and malfunctioning components.



My main analogue patch featured a Cwejman RES-4 in a loop with a Bananalogue Serge WVX. The combination of four frequency bands of oscillation might have been enough, but placing a Cwejman VCEQ-3 in the chain to dampen or boost the feedback added another level of complexity. A stressed coupling capacitor and scratchy Folds pot on the WVX added to the unpredictability and fun.

Live, I love my Clavia Micro Modular for two main reasons: patch recall, which allows me to set a scene or chop between moods, and polyphony. The virtual feedback patches in this set were simple, but switching them to two or three voices added complexity and interest, for example asynchronous panning or the beating of multiple sine-wave oscillators. You can do it with a ’real’ modular, but at a cost!

This set up is flexible and just about portable. It’s still completely live in that each patch either has to be built or played by hand. But the addition and convenience of the Micro Modular does cause me to question how we approach playing live with a modular. With many musicians turning up to gigs with their rigs pre-patched, is there a difference or even a need for the real deal?

Thanks again to Goldwiener, Hainbach, Paul da Fonk and Mark Berman of Powwow for the opportunity to make some noise.

Serge VCS Modification

Modifying the Doepfer A-171-2 Serge VCS for more extreme non-linear curves and more manual control over rise and fall times.



The Serge Voltage Controlled Slope is a classic design and an integral part of many modular musicians’ systems. The Doepfer A-171-2 is a faithful recreation of the original circuit. It works just like the Bananalogue VCS that has been in my case since pre-Maths times. That’s good, and bad.

The VCS easily allows one to set different contours for its rise and fall phases. But its non-linear curves are not as extreme as those possible with Maths. Setting times on the VCS is harder, as the useful range is limited to about 20% of the potentiometer’s throw. It’s these differences between these two similar function generators that this modification tackles.

The feedback that generates non-linear shapes is pre-wired on both the VCS and Maths. Calibrating the VCS output voltage from 5V to 8V has only a marginal effect. But if one patches the VCS envelope output to its ‘Both CV’ input with VC Rise + Fall set to linear, the Serge yields the desired curves. This suggests the internal CV feedback loop is capped.

Indeed, if we look at the left of the schematic, at switches SWF & SWR we find 330K resistors limiting the amount of feedback to the CV mixer to about 30%. If we lower this resistance we’ll get more feedback. I desoldered and replaced the 330K resistors with 200K but you could also try soldering another value in parallel e.g. 150K (= ca. 100K, 100%) or 470K (=ca. 200K, 50%).

This part of the modification helped clear up an oddity about the VCS: namely, why making the curves more exponential actually increases the overall envelope time. Negative feedback should make it shorter, and vice versa.

If we study the same part of the schematic again, we can see -12V across a 1M resistor feeding the summing points. Given the gain ratio set by the 100K resistor, this offsets the rise and fall rates by +/-1.2 volts. I find this counter-intuitive, so I removed both 1M resistors.



Both my Doepfer and Bananalogue modules are fitted with logarithmic potentiometers to manually set the rise and fall rates. This means, when using the VCS as an envelope or slew limiter, changes in the first 50% of the pot’s throw are imperceptible. Typical envelope settings lie between about one and three o’clock. Tapering the A50K potentiometers on the A-171-2 with a 5.6K resistor between the CW/ ‘hot’ lug and the wiper solves this. The useful range now spans from nine to three o’clock.



To solder these in place, you’ll have to unscrew the jacks and remove the board from the faceplate. I tape Gaffa around the ends of my pliers to avoid scratches. While you’re there, you can measure the output between the A50K wipers and the subsequent 82K resistors to understand how the log pots choke the voltage. I did try an S-curve taper with two sets of resistors but the quasi-linearization suggested here by Daverj worked best.

So, what does it sound like? Here are two recordings:

feeback mod: exp-fall, unmodified, 0:08 modded, exp-rise, 0:16 unmodified, 0:23 modded.

pot taper mod: cycling, rise = zero, fall manually altered. Stock VCS then modded at 0:39

These simple changes have given my VCS more whip and made it easier to use. Thanks to Dieter Doepfer for helping me read his PCB layout, Ken Stone for publishing his schematic, Tim Stinchcombe and Dave Jones.

If you’d like to try this yourself, take the usual precautions to avoid damage to yourself or your module. I will not be held responsible. If in doubt, ask Doepfer or your technician to carry out the modifications for you.

Patch Tips#18 - ADSR 'Free-Run'

Using a gate delay and comparator to trigger 'full length' ADSR runs, achieve looping ADSRs and delayed looping of AD envelopes. As suggested in this thread.



Unlike AD envelopes, ADSRs generally need a gate signal to fully complete their cycle. The gate determines the duration of the sustain phase of the envelope's run. So, what to do if your sequencer only generates triggers?

With a gate delay like the A-162, set the delay to zero and the length to taste. If using Maths' channel 1, the rise sets the delay time and the fall the length of the gate, available at the EOR. This provides the gate that the sustain requires. This mimics the response of AD envelopes like the VCS, which complete regardless of gate duration.

If you then mult that gate to a comparator with a suitable threshold, you'll get a second gate when the first expires. I used the Sport Modulator with the multed gate fed to the bottom input and 5V as a threshold reference sent to the top input. The middle output provides the comparator function. Mix the two gates and feed them to the input of the gate delay and you've got a looping ADSR.



The A-162 is great for these sorts of tricks and can also be used with AD envelopes which have an End Out (VCS, Maths, A-143-1) to achieve the Envelator's delayed looping.

Patch Tips #14 - Sub-Harmonic Division

Using Maths or the VCS to generate sub-harmonic variation.



Today's Patch Tip is cribbed from Seth Nemec's Bananalogue/ Serge VCS demos and the 'Undertone Generator' patch in Rich Gold's Serge book:

"Sub-Harmonic Generator: If a series of triggers are applied to the VCS faster than the total rise and fall times, the module will divide the incoming signal by a whole number. In the audio range the output will be the sub-harmonic series."

The VCS has the benefit of an AC-coupled output, but I feel Maths offers finer control over the settings. As this patch relies on the rise time, Math's EOR pulse can be used to provide an even beefier sub signal.

The technique simply involves patching a mult of your principal oscillator to Maths' trigger input and mixing either the envelope or EOR with the main VCO in a filter etc. Set the response to linear, fall to fully CCW and then gradually increase the rise time. Additionally altering the fall time will give you more control over the timing and hence sub-divisions.

Here's what it can sound like: subharmonix.mp3

The patch relies on the envelope's inability to respond to a second trigger until it has completed its cycle, meaning it will 'skip' pulses and thus generate a lower frequency. You can try this patch with other trigger-able envelopes like the Plan B Model 10, Cwejman CTG-VC or Doepfer A-143-1, bearing in mind that the minimum possible cycle time and trigger response will affect the possible sub-divisions.

Patch Tips#3 - Analogue Digital Logic

How to invert digital signals by analogue means.

Today's patch tip is the result of my frustration with Doepfer's A-160 clock divider and the fact that I don't own an A-166 Logic module.

The problem: the A-160 divides incoming clocks like this:



Which is fine for some applications but not when you want all divisions to start on the same, i.e. first, beat. Hook up a couple of sequencers or try to programme a 'straight' drum pattern with an A-160 and you'll soon see what I mean.

More often than not, I need divisions like this:



... exactly the opposite of what the A-160 pumps out.

An A-166 Logic module, with its two digital inverters, would offer a work-around. As I don't have one, I wondered if I could press one of my other modules into performing similar duties. I found the solution in my Bananalogue/ Serge VCS and Make Noise Maths.

Both offer an 'End Out' gate which goes high on completion of a cycle. Patching a Logical 'high' from the A-160 to their inputs causes the End Out to go 'low', in effect inverting the digital signal. For this to work properly, use the 'input' rather than 'trigger' jack and set both the rise & fall times set to zero. With Maths, use channel 4's EOC, rather than channel 1's EOR.

While I don't have enough modules to invert all the outputs of the A-160, this method at least allows me the option of forcing some to play 'on the one'.

It's the Envelope, Stupid!

An early Easter bunny.

(Repost from Easter 2008)

I dug these old tests out of the archive in response to these (1, 2) threads at Muff Wiggler's forum.

Bear in mind that this was 2008 and that the range of modules now on offer is far greater. Given the choice today, my recommendation would be the Cwejman CTG-VC and Make Noise Maths. Nevertheless, I hope the tests are still of use!

IT'S THE ENVELOPE, STUPID!

"Common wisdom has it that the most important module for shaping your sound is the filter. I beg to differ: it's the envelope, stupid!"

Download the test (3.3MB) here. Features Doepfer A-140, A-142, A-143-1, Cwejman ADSR-VC2 (rev.1) & Bananalogue/ Serge VCS.

Later that summer, I posted the following:

SOFT BOILED EGs

"Faster is better, right? Not necessarily ..."

Download the test (1MB) here for a comparison between the Roland MC-202 and Doepfer A-140 envelopes.

Sometimes 'sluggish' is just what you want.

Music Minute - Silent Night

An analogue carol for the festive season.

Featuring a Roland Super Jupiter, modular and EHX Poly Chorus and Stereo Memory Man w/ Hazarai.

Happy Holidays! Cheers, Navs.

Silent Night  by  navs

Patch of the Day - Harmonyhertz

I twisted my knee and had to undergo an MRI scan this week. For those of you who haven't had the pleasure, this is what it sounds like:

Harmonyhertz-PotD  by  navs

Having entered the machine, you're given a pair of noise-canceling headphones. The classical music that is piped through these is supposed to calm and distract you from the grunts and buzzes generated by the scanner. Don't know which device was responsible, but the kick and hi-hat pattern was a bizarre counterpoint. Sort of like a Clockwork Orange warehouse party. Someone with a sense of humour at Siemens, the company that built the contraption, decided to call it 'Harmony'. The nurse told me that the larger unit is called 'Symphony'.

THE PATCH

The patch features four voices: kick and hi-hat, ring modulated squarewaves, FM klunk and some 'ducked' classical music. Although I managed to use up nearly all of my patch cables, it was actually fairly straightforward.

Drums: MMF-1 sine wave kick, M12-filtered-noise hat. LFO provides rhythm, VCS provides gate delay for 'swing'.

Buzz: Wogglebug stepped out provides slow pitch changes for VCO-2RM. Two square waves, with a touch of XMod and manual pitch and PWM tweaking, are output from the ring modulator. Timing is generated by the burst out of the WB which is patched to a clock divider. The /8 gate signal triggers one Maths channel. An inverse /8 gate is fed to a second Maths EG so that the klunks are timed to occur after each buzz has sounded.

Klunk: M15 & AFG lin FM plus some pitch woggle and envelope thwapping from Maths and the mix out of an A-143-1. Maths' EOC used to trigger the Doepfer, klunk gated by M13 LPG.

Classical: Borg-filtered with a bit of FM from the combined buzz & klunk CVs. Vactrol speed in evidence as the CV takes a while to fade away from it's peak.

Ducking: this was achieved by sending the classical sample to the first channel of an A-134-2 VC Xfader, the audio mix of buzz and klunk to the second and applying the combined buzz and klunk CVs to the (asymmetrical) Xfader.

Hope you enjoyed the sounds and remember to look after yourselves!

This PotD dedicated with thanks to the docs and nurses.

Maths Test

This module needs little by way of introduction - shortly after it was announced, it sold out in the US and Europe. So what makes Make Noise's Maths so special that it prompted the largest used-envelope sell-off in Euro format history?

Have a listen for yourself:

Maths Test Taster  by  navs

Maths packs a pair of voltage controllable slope generators, much like the Bananalogue/ Serge VCS or Plan B Model 10, plus two channels of 'attenu-version'. It's this 'package' that is probably the key to its success. It's a compact, complete system. Most patch 'problems' can be solved without resorting to other modules and, like the Wogglebug, it's fun and inspiring.

In use, I found the envelopes clean and spike-free. Setting rise and fall times was far easier than on my VCS or Model 10. As the manual states, the contours have a dramatic effect on timing. Like the VCS, filtering audio is not one of its strengths but when used to slew CVs it is precise.

The only two things I missed were a single-shot trigger button and, more importantly, voltage control over the polarizers. The latter would, for example, allow VC contours and greatly enhance the mathematical possibilities!

You can download the full test here (13.5MB)

Update: here's a short clip demonstrating Math's slew/ portamento capabilities.

Patch of the Day - Long Way Down

Something gentle for a Sunday afternoon:

PotD_longwaydown  by  navs

Live, four-voice patch with manual tweaks.

Self-oscillating Cwejman MMF-1 dual-peak sine modulated by WB smooth out. A-Sol SH-NZ noise to Plan B Model 12 HPF, VCA VC'd by Doepfer A-147 VCLFO sine, itself VC'd by the output of a A-156 Quantizer. Ring Mod output of a VCO-2RM filtered by a Malekko/ Wiard Borg, envelope from Bananalogue/ Serge VCS VC'd by Woggle out. M15 VCO (linFM) gets WB stepped, gated by M10 envelope which is triggered by WB burst and VC'd by stepped out. M10 EOC to A-142 envelope which provides the voltage which is then quantized by the A-156.

Patches. They always start out simple, don't they ...

Patch of the Day - Bugfest!

A 10 minute modular jam to close the month.



Everybody modulated everybody else. Enjoy!