Friday, 23 April 2010

Patch Tips #9 - A-119 as Frequency Doubler

The A-119 External Input module can be used to double the frequency of an LFO when used for clocking purposes. Here's the how and why:

Patch a square wave LFO to the A-119's asymmetrical input, set the input gain so that no clipping occurs and then adjust the threshold level to attain a 'clean' signal from the gate out.

Here's an example featuring the original and doubled clock:

Because the A-119 features a full wave rectifier to accomplish its envelope following duties, the negative half, or 'off' period, of the square wave is flipped into positive territory, in effect doubling the frequency.

There is a slight delay to the doubled clock, but this is understandable due to the speed of the A-119 and the threshold necessary to avoid a standing, permanent gate.

In the second example, I've also taken the sine output of the LFO and fed to a wave multiplier to get a third, syncopated clock:

Feeding the wave multiplier with a triangle wave will yield different clocks. For more wave-folded beats, see this post.

Sunday, 18 April 2010

Patch Tips #8 - More Feedback

Getting the Plan B M12 SVVF to self-oscillate and 'sine-shaping' à la Bubblesound µLFO. An update to this post and part of my ongoing drive to sell the Doepfer A-133 VC Polarizer.

If you've read that post, you'll know how I go about this so, without further ado, here's the Plan B M15 sine being fed back to varying positive and negative degrees:

And here it is being used as a modulator:

I don't have a µLFO and don't know the Bubblesound circuit, but this certainly seems to yield similar results:

I'd be interested to hear from any µLFO users whether the sine-shaping also causes a change in frequency as per my examples.

Feedback with the Model 12 yields some very interesting results! Depending on the amount of feedback, internal resonance setting and input gain, I got some wonderfully wild sounds. This is the bandpass output being fed-back negatively:

Part of the sound is down to clipping on the input circuit as you can see from these 'scope shots:

Surprisingly, I found that it is possible to FM the M12 at audio rates, although of course not with the precision or clarity you'd get with a non-vactrol-based filter:

The sine output of the M15 was used to FM the M12. The output of the filter was also sent to the sync input of the VCO, resulting is some pleasing, if groggy, harmonic stepping.

Tuesday, 13 April 2010

4MS Rotating Clock Divider

First impressions of the 4MS Rotating Clock Divider.

This colourful module is an update on the classic clock divider design, offering even and un-even divisions of 1 to 64 and a unique rotate function to shift the resulting triggers along its eight outputs.

Here's a run-through featuring four voices. Towards the end, a random CV is applied to the rotate function.

The next example focusses on the rotate function, which is addressed via a CV. While this is more complicated than stepping with a gate, it allows programmed timing-changes with a sequencer or preset controller like Pressure Points.

The RCD outputs triggers, rather than gates. This is useful for percussive material, but has implications for certain logic gating functions. In this example, the main clock is AND-gated by the /4 output, first with a Doepfer A-160, then with the RCD.

The RCD will also function as an audio sub-divider. Here too, the results are different to the A-160 because of the lack of gates.

Sine wave source mixed with 'divided' signal. Choices joystick used to first rotate and then also change pitch.

The following example uses the RCD as a simple three-voice sequencer. The clock is reset on the first beat of the bar until the 1:25 mark (shortly after the FM index riser). Thereafter, the divisions are allowed to run free until about 1:50 (after the decay of the open high hat is lengthened) when it is snapped back into sync. A joystick was used to provide the rotate CV.

This was a lot of fun, but it did highlight an issue common to both the RCD and A-160: neither play 'on the one'. This is apparent when the drums are faded in (0:30). The cymbal denotes the down-beat, the RCD is playing off-beat. This can be 'corrected' on the A-160 with a logic inverter but, as the RCD outputs triggers, this is not possible. Another thing that became clear was the need for some planning with a programmer to set appropriate divisions, rather than wiggling a joystick!

The RCD got me thinking and working in a way I hadn't previously and I wanted to see whether the A-160/ 1 could compete. In this recording I mimicked the previous patch with the Doepfer clocking modules and fed four different reset triggers via an A-151 sequential switch which I stepped with a manual gate.

This resulted in less drastic changes than rotating divisions, but the shifting rhythmical patterns were no less musical or interesting. I also got the impression that the Doepfer divider had a bit more 'funk' than the 4MS, but this might just be down to timing inaccuracies on the part of the A-160.

The 4MS Rotating Clock Divider is mesmerizing, immediate and a lot of fun. Having easy access to un-even divisions was a revelation and the reset possibilities allow for complex rhythmic patterns. I'm not sure I'd want it as the only clock divider in my system, but it could certainly fulfill that role.

To wrap things up, today's Patch of the Day features the RCD and Plan B's M23 ASR.


Two VCOs, panned left and right receive shifted pitch and trigger information. A Wogglebug provides a random CV to rotate the RCD, modulate Maths' envelope length and transpose the sequence.

Monday, 5 April 2010

Patch Tip #7 - Synced Transposition

Today's tip is adapted from Rob Hordijk's excellent Nord Modular tutorials.

Here's the situation: you have a clocked sequence that you want to manually transpose with Pressure Points. Try as you might, your timing isn't precise enough to avoid pitch glitches:

In the above, PP's row 1 CV was patched directly to the transpose input of an A-156 QNT. Taking the CV and first patching it to a sample & hold, which is triggered by a clock division, synchronizes the manual changes:

Hordijk's patch is a little more involved, but in the second example I simply used an inverted output of the A-160 to trigger the S&H. Another option would be to use the 'step1' output of an Analogue Solutions SQ8.