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. 

Sunday, November 9, 2014

Using Key Follow/Tracking with a Modular

Key Tracking/Follow basics:

We've all seen Key Tracking or Key Follow on a synthesizer's filter section, right?   An analog synth's keyboard creates a voltage which is used to play the oscillators in tune up and down the keys.  Applying this voltage the the filter section can make higher-played keys sound brighter and lower keys sound more dull (in the case of a LPF).  If your filter can self-oscillate and is calibrated to 1V/Oct, you can use the oscillating filter as an extra VCO of sorts, simply tune the Fc to suit the pitch of your VCOs.  Some synths with multiple VCOs might also have a switch to turn Key Follow off for one or more of them, so that they can be used as FM sources.  These are the standard applications found on most synthesizers.  But we're here for modular applications, yeah? 

Example 1:
Key Follow // Logic (Reverb Send)

Have a look at this patch I created on  

Imagine that the Bus Access module is delivering the MAQ Row 1 sequence (or keyboard) CV and Gate to the system.  This CV not only controls the VCO 2 pitch, but also affects the Voice 1 Filter Cutoff, but the point of this patch is that this CV sequence is also sent to a Boolean Logic moduleA 16-step gate pattern from the MAQ Row 1 is also routed to the Logic module.  

When you play above a certain key (> +2.0V for the Doepfer A-166 used here) the Logic AND circuit allows the gate signal to trigger the reverb patch.   The trigger is passed through AND to the ADSR which controls the VCA at the Reverb's input, like an automated effects send.  (Note: this ADSR can be omitted if necessary and the gate/trigger can be fed directly to the VCA's CV input, or smoothed a bit first by using a lag processor / slew limiter)  

Now any low notes you play will remain dry and notes above +2V will have reverb applied (this is adjustable by using an offset generator, attenuator, or amplifier).  If you chose to use the ADSR for the send VCA, the full envelope will be heard with reverb.  If you omitted the ADSR, the reverb will simple be fed with the pitch that occurred for the duration of that step/key.  The Logic AND could be controlled by something else instead, like a joystick, LFO, sequencer, velocity CV, etc, but key follow works too and makes it all dependent on the key you press rather than something timing-based or something that would require a free hand.  Check out this audio/video example below.  

In the video below, at first the patch is the one shown above, but the patch changes to this towards the end which uses the other half of the Logic module (XOR output) and the /2, /8, and /32 outputs of an A-160 Clock Divider to alter the trigger pattern sent to Voice 1 (Bass). 

Example 2:
Inverted Key Follow // VC Decay

A modular system is open to many more voltage processing possibilities than most synthesizers on the market.  As I said earlier, most synths only allow you to use key tracking for VCO pitch and VCF frequency.  However, there are some that have mathematical functions as part of their modulation matrices (like my Waldorf Microwave XT and E-mu E6400 Ultra).   These will let you use Key Follow as a modulation source, process the signal, and route it to a variety of destinations.  Similar patches can be created in a modular system. 

One patch I’ve used takes the keyboard/sequencer CV signal and inverts it, so the higher up the keyboard you play, the lower the voltage becomes at the inverter output.   I’ve used this in combination with a Doepfer A-142 VC Decay module and a VCA to let low notes maintain the maximun Decay time (set by the Decay control) while high notes will have a Decay time altered by the voltage at CV In. Because the Key Follow signal was inverted, higher-played notes will have a Decay time equal to Decay Control value minus Sequence CV value.  This allows a single sequenced loop to provide both a bassline and higher accent notes which are easily distinguishable.  

See the basic patch example here:

In the video clip below, I used a more involved version of this same patch.  The patch you will hear in the video looks more like this (:

This first video first shows a rising progression of notes with Inverted Key Follow applied to the A-142 VC Decay/Gate.  Then the MAQ is switched to Random direction and sped up.  A joystick and VC Switch is used to disable the Inverted Follow, so all notes are of equal length while the joystick is held to the right. 

This next video shows the same patch driven by a different MAQ sequence.   While the modular patch was recorded, I used the Joystick to disable the Inv CV to the VC Decay, and LFOs were free-running to modulate the patch.  Other sounds were added after the modular take to show how it might work in a "track".

There are a few manual controls:   

-  The Manual Gate's Output 2 is used to reset the Clock Divider and Transpose Sequencer before pressing PLAY (since I did't have a Reset set up from a MIDI/CV converter).  

-  An A-174 Joystick was used to toggle one half of a Dual VC Switch.  This half of the switch module toggles between the Inverted Key Follow signal and NO signal, so that I can remove the Inverted Follow effect momentarily and then reactivate it at the same depth.  

There is Logic at work:

In this patch, the top half of the A-166 is used to "mute" the sequence.  Input 1 is the Gate Out pattern from Row 1 of the MAQ16/3.  Inputs 2 and 3 are the /4 and /32 Outs from the A-160 Clock Divider.  This way, the envelopes are only triggered when all three inputs are HIGH (this changes for a section of the video, when just Row 1 gate pattern is used).

The bottom half of the A-166 is used in combination with a modified A-119 Envelope Follower.  I modified the module to let me use the internal comparator (which normally tracks the follower signal) with any external signal, in this case, the main CV sequence from the A-156.  The THRESHOLD is set so that only the highest notes of the sequence create a GATE OUT signal.  This gate is sent to the bottom Logic.  The AND output from the top Logic is also sent to the bottom section.  Now, only the highest notes of the sequence will trigger the ADSR/VCA which feeds the SR-01 Reverb, and only when the trigger sequence is "unmuted" (top, Logic AND).  This is all similar to Example 1, above, but uses a comparator for its threshold setting, rather than being stuck to a 2V threshold if using the Logic module alone. 

There are three voices, all playing simultaneously from the same 16-step sequence.

  -  Voice 1: Z3000 Saw and Square waves through A-109 (#1) VCF into A-125 Phase Shifter, then to A-199 Spring Reverb, finally back to the A-109 (#1) VCA.  The TipTip Z3000 receives CV sequence from MAQ Row 1 via A-156 Dual Quantizer, transposed by A-155 Row 1.  A-109 Fc is modulated by A-156 CV sequence (key follow) and by A-140 ADSR.  A-109 VCA is controlled by A-142 Env Out.  VCA out to A-138 Mixer.  Phase shift is controlled by an A-148 Dual S+H module, with an A-143-3 LFO as the sample source, and the MAQ Row 1 Gate pattern as the trigger.  The Reverb feedback is patched through an Analogue Solutions SY02 Multi-mode filter (MS-20 clone) and modulated with another A-143-3 LFO to the HPF CV In. 

  -  Voice 2: A-111-1 (#1) Sine to A-131 (#1) VCA, Audio In 1.  A-111-1 (#1) Saw to A-124 Wasp VCF (HP) out to A-131 (#1) VCA out to A-138 Mixer.  A-111-1 receives sequence CV from A-156 via top half of A-170 Dual Slew.  A-124 Wasp is modulated by one unit of an A-143-3 Quad LFO.  VCA is controlled by A-142 Env Out.

  -  Voice 3: Z3000 Saw to A-115 Audio Divider out to A-109 (#2) Audio In.  A-109 VCF Out to A-131 VCA (#2) to A-138 Mixer.  VCA is opened by an A-140 ADSR controlled by the Gate Output of the A-142 VC Decay module.  A-109 VCF Q is moduated by an A-143-3 LFO.  VCF Cutoff is modulated by a combination of sources.  An A-146 LFO Pulse is sloped by the lower unit of the A-170 used in Voice 2, and then attenuated into CV2 In.  Next, outputs from another LFO and another VCO are patched to an A-135 VC Mixer.  Their levels are modulated by another two LFOs.  The Mixer output is send to VCF CV1 In.  The Pitch of this VCO is also controlled by the main CV sequence from the A-156 Quantizer.  The VCF Out is also sent to an Analogue Solutions SR-01 Spring Reverb.  The SR-01 output is boosted by an A-119 Ext. In module and fed to an A-123 24dB HPF.  The HP output is sent back to the A-109 VCA In controlled by another A-140 ADSR.  VCA out to input 4 on the A-138 Mixer.  The A-140 controlling this VCA is triggered through the bottom half of the A-166 Logic (inputs = AND from top of A-166 + A-119 comparator out, see above)