Monday, November 10, 2014

More A-155 Tricks: A Way to Shuffle Your Patterns

   Continued from my previous A-155 posts, but applicable to any analog sequencer being driven by an external clock... 

   Another difference between the current range of Doepfer Sequencers is the ability to apply a shuffled groove to your pattern.  The MAQ16/3 and A-155 do not have this feature, but the DarkTime does.  However, I don't have a DarkTime ... so I wanted a way to shuffle patterns on my A-155 using other modules.  [I say "using other modules" because the easiest way may be to program a shuffled trigger pattern in another sequencer or drum machine and feed that to the A-155 through either a MIDI/CV interface or the drum machine's Trig Out socket.   This way you are able to have rests in your pattern without affecting when the shuffled note occurs (as you might if using a Switch module)].   Since I like to have more manual, hands-on control, I wanted to create the shuffle and rests within the modular system.  There are a few modules available today that can provide a shuffled clock, like the Shuffling Clock Multiplier from 4MS.  But I don't have one of those either....yet (update: still).

   I'm assuming you all know what Shuffle is (also called Swing), but just to be clear (although, in my own words), it is the shifting in time of certain notes/steps in a pattern.  A "Quantized to 16ths" pattern would have the same period of time between all notes, a shuffle ratio of 50%.  A "shuffled" pattern would typically shift even-numbered notes to be later in time.  If looking at the pattern on a grid, the even notes would shift to the right.  In this image, you can see that the Quantized pattern has a 50% ratio ... the Even steps (Red) are half-way (50%) between the Odd steps (Blue).  The Shuffled pattern shown has a ratio greater than 50% (more than half-way). 

   My preferred method....

   The best way I found to generate a shuffled A-155 pattern from a constant clock source requires only a trigger delay, like an A-162 TDEL, a Trigger Combiner, and some multiples.  Some other modules can be added to this patch to make it more versatile, like manual switches and clock dividers, but they are not necessary for a quick test.  It isn't obvious in the images because the first mult is not shown (instead represented by two arrows coming from the clock source), but you MUST USE A TRIGGER COMBINER FOR THE SECOND MULTIPLE otherwise the two multiples are connected causing feedback into the trigger delay. This could be an actual trigger combiner module (like a multiple but with a diode for each Input, all connected to a single Out), a Logic OR circuit, a linear active mixer, etc. Here's how it would feedback...  

  Take a clock source in 8th note time for the tempo in which you wish to work. This can be from an LFO (preferably one like Doepfer's A-146 which has variable pulse width), MIDI/CV Clock out, 8th note trigger pattern, etc.  Using an 8th note pattern gives tons of space to work with between pulses, but to tighten things up a bit more and have all notes the same length, you should shorten the pulse to resemble a 16th note.  This would be referred to as 25% PW.  Either adjust it with the LFO's pulse width control, or use half of the A-162 to create a timed pulse (no delay, length adjusted to fit tempo).  Alternatively, if your LFO provides both Square and Pulse Outs and you are using a Trigger Delay with features like the A-162, you can eliminate the first multiple (only needed to split the LFO into two signals) by sending the Square Out to the Trigger Delay and the Pulse Out to the Combiner.  The A-162 can be used to reshape the Square to a similar width as the Pulse.  If using a MIDI/CV Clock source, shorten the MIDI notes to 16ths spaced 1/8th apart.

   Split the clock source (shown above as two arrows from the LFO) and send one path to half of the A-162 and another path to your Trigger Combiner.  Send the A-162 output to the Trigger Combiner as well.  Patch Trigger Combiner Out to the Clock Input of the A-155.  The A-162 creates the shuffle by producing a delayed version of the 8th note clock.  Of course, timing it to 50% would produce a quantized 16th note pattern, but that defeats the purpose...

(To calculate this trigger delay period in milliseconds, use this formula: 
a 16th note's duration is 15/BPM.  For example, if your song tempo is 120BPM, 15/120=.125sec or 125ms)  

With this method, the shuffled notes can be placed > or < 50%, which is quite unique as most machines with shuffle only allow ratios >50%.  Perhaps ratios <50% are techincally known by another name?

  If a rest occurs in the original clock signal (the odd steps), no shuffled note will appear in the following even step as there is now no pulse from which to create the delayed pulse. Therefore, in my example, the shuffling clock remains consistent, and rests are programmed using the Gate/Trigger assignment switches on the A-155 sequencer itself (shown below).  This allows the user to change the pattern as it plays, inserting rests on any step, odd or even.

   Adding Shuffle ON/OFF ...

   If you happen to have a few more modules, you can add an ON/Off switch so you can go from a set shuffle to no shuffle without changing your trigger delay setting.  The modules you'll need are an A-160 Clock Divider (or similar) and a manual A/B switch.  As shown in the diagram above, you will get two versions of the clock signal: a /2 version (16ths) and a /4 version (8ths).   

[edit: I realize after reviewing this that increasing the clock rate and using two divisions is likely unnecessary, and I can't recall why I did it this way.  It's been over a year, so perhaps there was a reason that I've since forgetten.  It seems appropriate to use the master clock and a /2 division as the 16th and 8th note patterns...] 

The manual switch selects either the 16ths, or the shuffled 8ths as in the previous patch.  I built a simple module with a few SPDT toggle switches for this.  You could use an A-150 VC Switch and a CV source (A-176-type CV Source, an un-sprung Joystick, etc) to switch them also.

  A similar shuffle method ...

   If you are using a constant clock source (16th notes with no rests) and creating rests with the A-155 trigger assignment switches, you can use an A-151 Quad Seq Switch (or similar) to cycle between a normal trigger and a shuffled trigger.  This method does not require using a Clock Divider.

   A 16th note clock source is sent to a multiple and from there to an A-162 TDEL and to the Trig In of the A-151, as well as I/O1 and I/O3.  The TDEL output is sent to another multiple and from there to I/O2 and I/O4 of the A-151 Seq Switch.  Each master clock pulse generates the normal clock, the delayed variation of the normal clock (through the A-162 TDEL), and the trigger which forces the Quad Sequential Switch to alternate between them.

Shuffle using A-162 (or A-142) and A-165

  After publishing the above methods, I was contacted by musician/author Florian Anwander who realized a clever way to achieve a manually adjustable shuffled clock using Doepfer's A-165 Trigger Modifier module.  I don't have this module so had not considered its applications.  Many thanks to him for suggesting this patch!

  The A-165 has two functions: it can invert a trigger input signal (high input = 0V output, low input = high output), and it can produce a 50ms pulse at both the rising and falling edges off the input signal. Rather than using the A-162 TDel's DELAY setting to create the shuffle, now you can use the LENGTH setting instead. As the A-162 is a dual module, one sub-unit can be used to set the space between 50ms pulses (the shuffle ratio), and the other sub-unit can be used to set the pulse width of the final signal used for Sequencer Clock and/or ADSRs.  Just make sure that the Length set by the second sub-unit does not overlap the next master LFO/Clock pulse.  

  The example patch below shows a common Square LFO shape (50% pulse) as the clock source.  Alternativley, an LFO with a variable pulse width (like the A-146 in the above examples) could be used instead of the first A-162 sub-unit, and an A-142 VC Delay/Gate module could be used in place of the either A-162 sub-unit.  The second sub-unit's function is not entirely necessary. 

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