4ms Company SCM Plus Shuffling Clock Multiplier Module User Manual
- June 9, 2024
- 4ms Company
Table of Contents
4ms Company SCM Plus Shuffling Clock Multiplier Module
The SCM Plus is a clock multiplier with eight gate outputs and complex beat manipulation features. It combines the classic Shuffling Clock Multiplier (SCM) and SCM Breakout (SCMBO) into a single module using higher precision hardware than its predecessors.
SCM Plus features:
- Eight gate outputs, each multiplying up to x32
- Five slipped/shuffled/skipped clock outputs and three steady clock outputs
- Five knobs with CV jacks:
- Rotate shifts multiply-by amount
- Slip causes particular beats to land ahead in time
- Shuffle selects which beats are affected by Slip
- Skip omits certain beats in a pattern
- Pulse Width controls width of output pulses
- Resync trigger input resets the slip/shuffle/skip counters
- 4x Fast button and gate jack increase multiply-by amount by a factor of four
- Mute button and gate jack stop all outputs
- Save Clock feature restores last saved tempo when powering up
- Clock Bus jumper allows module to receive tempo from other modules over the power bus
- Free Run jumper allows unit to operate without an external clock
- LED dimmer trimpot allows for custom LED brightness
- 12HP Eurorack module
Setting up your SCM Plus
- Power off your Eurorack system.
- On the back of the SCM Plus you will see a 16-pin header. Connect one end of the included power cable to a 16-pin Eurorack power header on your power supply distribution board and the other end to the SCM Plus with the red stripe on the power cable oriented towards the bottom of the module.
- Using the included screws, securely attach the SCM Plus to the rails of your case.
- Power on your Eurorack system.
Note: The SCM Plus is reverse-polarity protected, but incorrectly connecting any module in any system can damage other modules on the power bus.
Clock Input Jack
The clock In jack is triggered by a rising edge of at least 2.5V. The light will blink red in time with the incoming clock signal.
Clock Output Jacks
The eight output jacks produce gates which can be used with a variety of
Eurorack modules such as envelope or function generators, drum modules,
sequencers, samplers, or anything that accepts a trigger, gate, or clock. They
also can be used to open VCAs, ping resonant filters, or even as crude lo-fi
audio signals.
x output jacks (x1, x2 and x8) are the three steady clock outputs. These are
not affected by Slip/Shuffle/Skip parameters. Their associated lights will
blink blue in time with the outgoing clock signal.
S output jacks (S3, S4, S5, S6 and S8) are the five slipped/shuffled/skipped
clock outputs. Each is based on a multiple of the input clock frequency (x3,
x4, x5, x6 and x8, respectively). Their lights will blink green in time with
the outgoing clock signal.
Parameters
Resync
Applying a trigger greater than 2.5V to the Resync jack will cause the beat
pattern to start over. The beat pattern is established by the Skip, Slip, and
Shuffle parameters. Resync is not the same as a typical “Reset”. A clock
multiplier has no dedicated reset jack because it resets on every clock input
pulse. That is, the pattern starts over every time a clock is received on the
main In jack. The Resync jack allows for shifting the phase of the beat
pattern so that it (re-)starts somewhere in between clock pulses.
Example Patch
The easiest way to hear this feature is to run a very slow clock into the
clock In jack (try 4 seconds between pulses). Then turn Skip, Slip, and
Shuffle to some randomly chosen setting. Next, plug a manual gate (eg: FSR-4
or Pressure Points or Choices) into the Resync jack. Listen to the S8 jack and
try to memorize the beat pattern. Now trigger the Resync jack and hear how the
beat pattern instantly re-starts. It will re-sync itself back to normal when
the next clock pulse appears on the In jack, so the new beat pattern will only
last for less than one measure.
Rotate
The Rotate jack and knob rotate the clock multiply-by amounts throughout the
output jacks (see Multiply-By Amounts Table ).
With no rotation (knob turned down and no CV on the jack) the x1 jack outputs a clock equal to the input clock, the x2 jack outputs a clock twice the tempo of the input clock, the S3 jack outputs a clock based on three times the input tempo, etc. up to the x8 jack which outputs a clock eight times the input tempo. As rotation is applied by turning the knob up or applying CV to the jack, each jack’s multiply-by amount shifts downward, wrapping back to multiply-by-eight after multiply-by-one. So when the knob is turned up a small amount, x1 outputs a x8 clock, x2 outputs a x1 clock, S3 outputs a clock based on a x2 tempo, etc. up to x8 which outputs a x7 clock. As more rotation is applied, x1 outputs x7, x2 outputs x8, x3 outputs x1, etc. At maximum rotation, x1 outputs x2, x2 outputs x3, etc., up to x8 which outputs x1.
When the jack is not patched, the the knob will set the amount of rotation.
When a cable is patched into the jack, the knob attenuates the jack’s signal.
Turning the knob fully counter-clockwise will make the jack do nothing.
Turning the knob fully clockwise will let a 3V signal on the jack perform the
maximum amount of rotation.
Keep in mind that the “x” jacks always output steady clocks, and the S jacks
always output slipped/shuffled/skipped clocks, no matter what amount of
rotation is applied.
Slip
The Slip knob and jack shift every “n” beats forward in time. The value of n
is set by the Shuffle parameter, and the amount by which each beat is late is
set by the Slip parameter. For example, if n=2, then every other beat lands
late: beats 2, 4, 6, etc…
When Slip is set to zero (when there is no CV signal or the knob is turned fully counter-clockwise) the S output jacks behave like the x output jacks, with no slipping or shuffling. However, Skip may still cause beats to drop out. Increasing Slip a small amount by turning up the knob or applying CV to the jack causes some beats to land slightly late. Turning the knob all the way up or applying maximum CV causes some beats to land right before the next beat.
When the jack is not patched, the the knob will set the amount of slippage.
When a cable is patched into the jack, the knob attenuates the jack’s signal.
Turning the knob fully counter-clockwise will make the jack do nothing.
Turning the knob fully clockwise will let a 3.3V signal on the jack perform
the maximum amount of slippage.
Internally, there’s a counter that keeps track of whether each beat should be
slipped or not. This counter resets itself on each input clock pulse. For
example, if we have a steady clock input and we’re slipping every other beat,
beats 2 and 4 will be late on the S5 output jack. If we have an input clock
coming in before beat 6 is supposed to land, the counter resets, beat 6
becomes beat 1, and beat 1 is on time. So then beats 7 and 9 are late. The
Resync jack resets this counter.
Note: Pulse Width (PW) affects how much slippage can occur. With very wide pulses, there’s very little time between the end of a beat and the start of the next beat — therefore there’s very little room to push the beat forward without encroaching upon the next beat. The shorter the PW setting, the more dramatic the Slip effect.
Shuffle
The Shuffle jack and knob work with the Slip parameter. While Slip controls
the amount by which certain beats are pushed forward in time, Shuffle controls
which beats are slipped. The default setting is every other beat (Shuffle at
minimum). As you turn Shuffle up, every third beat will be slipped, then every
fourth beat, fifth, sixth, and finally at a certain point in the knob’s range,
every seventh beat will be pushed forward. From this point in the range to
maximum, Shuffle begins to push groups of beats forward instead of pushing
just one beat forward. So next, a group of two beats are slipped, then a group
of three, etc.
The knob sets an offset, and the jack signal is added to the knob’s setting. When the knob is fully counter-clockwise, a signal from 0V to 5V on the jack will sweep the entire range of Shuffle patterns. When the knob is fully clockwise, a signal from 0V to -5V will sweep the entire range.
Skip 
The Skip jack and knob are used to drop beats out of each measure. The concept
of the measure is based on 8 beats. The jacks that output less than x8 are
considered to be the first “n” beats of the measure (e.g. S5 output jack is
considered to be the first 5 beats of a measure). With Skip at minimum, all
beats are played. As you turn the Skip knob up or apply a positive CV, more
and more beats will be dropped.
The pattern of dropped beats is determined by a lookup table in the SCM Plus
code. Each voltage corresponds to a particular pattern in the lookup table.
There are 128 entries in the table, which range from 0 beats dropped, to each
one of 8 beats dropped, to every permutation of 2 dropped beats, to every
permutation of 3 beats dropped, to (nearly) every permutation of 4 beats
dropped out of an 8-beat measure. Then the table is inverted, so that it
continues to 5, 6, and 7 beats dropped. Dropping all 8 beats is avoided, since
the Mute feature has this same functionality.
The knob sets an offset, and the jack signal is added to the knob’s setting.
When the knob is fully counter-clockwise, a signal from 0V to 5V on the jack
will sweep the entire range of Skip patterns. When the knob is fully
clockwise, a signal from 0V to -5V will sweep the entire range.
Pulse Width (PW)
The PW (Pulse Width) jack and knob effect all eight output jacks. With PW at
minimum, each jack will output a very short pulse (1ms when frequency is under
1kH. This is enough to trigger most other modules. At the PW knob’s center
setting, the pulse width will be 50%, which is a square wave. In this state,
the amount of time the wave shape is low is equal to the time it spends high.
At its maximum setting, the pulse width becomes very long, in that it only
blips low for about 300us. This is functionally an inverted trigger. One thing
to watch out for with a very long pulse width is that the
Slip/Shuffle parameters will have only a slight effect. This is because Slip/Shuffle push the beats forward in time without changing their pulse width. So when the width of the signal is very long and the gap between the pulses is very short, there isn’t much room to move without completely closing the gap between pulses. Therefore, not much slipping can occur. To best hear the Slip/Shuffle effects, keep PW at 50% or less. Another way to think about this is that PW is a way to decrease the amount of Slip effect without changing the Slip parameter itself.
The knob sets an offset, and the jack signal is added to the knob’s setting. When the knob is fully counter-clockwise, a signal from 0V to 5V on the jack will sweep the entire range of PW. When the knob is fully clockwise, a signal from 0V to -5V will sweep the entire range.
4x Fast
The 4x Fast jack and button make every output run four times faster. The
button will shine orange whenever this feature is engaged. Pressing the button
will toggle the 4x Fast feature, and so will applying a signal greater than
2.5V at the jack. When the button is off, a low voltage on the jack disables
4x Fast, and a high voltage enables it. When the button is on, a high voltage
turns 4x Fast off, and a low voltage enables it. Said another way, any time
the button is pressed or the jack signal goes high or goes low, the 4x Fast
feature will toggle states. Example Patch: 4x Fast
Connect one of the SCM Plus outputs to the 4x Fast input (e.g. try the x2
jack). When the jack goes high, everything will speed up, including the signal
you are currently sending to the 4x Fast jack itself. So when this signal
flips low, everything slows down. This is a very simple way to create a
chaotic rhythm pattern. Playing with PW dramatically affects the pattern.
Mute
The Mute jack and button prevent any jacks from turning on. The button will
shine orange when this feature is engaged. Any output jack that is already
outputting a high signal will continue on its normal timing, but when it goes
low it will stay low as long as the Mute gate is held high.
Pressing the button will toggle Mute, and so will applying a signal greater
than 2.5V at the jack. When the button is off, a low voltage on the jack
disables Mute, and high voltage enables it. When the button is on, a high
voltage turns Mute off, and a low voltage enables it. Said another way, any
time the button is pressed or the jack signal goes high or goes low, the Mute
feature will toggle states.
Getting Started Patch
A good way to start is to first turn the knobs to their default settings: Shuffle, Skip, and Rotate all the way down (counterclockwise); Slip and PW centered. Press both buttons off so that 4x Fast and Mute are not illuminated.
Run a slow clock into the In jack, and use the S8 and x8 output jacks to open two different VCAs, Low Pass Filters or Low Pass Gates. If you have envelope generators, patch x8 and S8 to the trigger input of envelope generators and then patch the envelope outputs to the VCA/LPF/LPG control inputs. If you don’t have envelope generators you can just patch the x8 and S8 jacks directly to the control inputs on Page 5 of 8 the VCAs/LPFs/LPGs. Run sound sources into both VCAs/LPFs/LPGs and mix the outputs together so you can hear both at the same time. Make sure Rotate, Shuffle, and Skip are turned all the way down, and that PW is centered to 50%. Adjust to suit your ears. Now play with Slip, slowly turn the knob along its full range and listen to how every other beat from the S8 jack lands later and later as you increase Slip. Next, nudge Shuffle up until the beat pattern changes. Play with Slip some more, and keep nudging Shuffle up and playing with Slip. Once you get a feel for all the possibilities with those two knobs, start playing with the Skip knob: you should hear some beats drop out of the S8 output, but the x8 output will continue thumping steadily along.
How it Works
The SCM Plus measures the time between the previous two pulses and uses that value to calculate the frequency of the clock signals on the output jacks. Applying a steady clock will produce an output clock of equal frequency on the x1 jack, a clock of double the frequency on the x2 jack, and a clock of eight times the frequency on the x8 jack.
If the Free Run jumper is installed (see section below), you can simply send
two clock pulses into the clock input, and the SCM Plus will run at that tempo
indefinitely. There is inherently some tempo drift in taking this “tap tempo”
approach. If your goal is to synchronize the SCM Plus to another clock, using
a common input clock is recommended. The SCM Plus can handle rapidly changing
clock signals, including complex waveforms that cross the 2.5V boundary at
erratic intervals.
Three of the jacks will always produce regular clock pulses that are multiples
of the input clock: x1, x2, and x8. These jacks are not affected by the Slip,
Shuffle or Skip effects.
The other five jacks (S3, S4, S5, S6, S8) produce clocks that are also
multiples of the input clock, but these jacks will “rag” the beat (Slip and
Shuffle), as well as drop some beats out (Skip).
Notice there is no S7 jack. This tempo pattern can only be produced with the Rotate knob or jack. For example, looking at Multiply-by Amounts At Each Jack table on page 8, we see that 0.6V on the Rotate jack will make the S6 jack output S7, or applying >2.9V will make the S8 jack output the S7 pattern and the x8 output x7. The reason for leaving out S7 was to make room for both S8 and x8: playing a non-slipped and a slipped clock at the same time results in some fascinating phasing and variable-shifting effects, especially if Slip is modulated slowly and both tempos are heard side-by-side (see the Getting Started Patch above).
Saving the Clock
The current tempo can be saved and restored the next time the SCM Plus powers
on with the Free Run jumper installed.
To save the current tempo, the following button sequence must be executed
without allowing more than half a second between button presses:
- Begin with the module not muted and no voltages toggling Mute or 4x Fast.
- Press and release Mute to engage Mute
- Press and release 4x Fast
- Press and release 4x Fast again
- Press and release Mute to disable Mute
Whenever the SCM Plus turns on with the Free Run jumper installed, the last saved tempo is restored. Note that if you have a clock patched into the In jack or an active clock on the Clock Bus (and the Clock Bus jumper installed), the incoming clock will override the saved tempo.
Free Run Jumper
On the back of the module is a jumper labeled Free Run. When this jumper is
installed, the SCM Plus will run whenever it’s not Muted, even if there is no
external clock. This means that if you unpatch the In jack and/or stop the
upstream clock, the SCM Plus will keep producing multiplied clocks at the last
tempo it received. Those familiar with the legacy SCM module will recognize
this as the default behavior of that module.
When the Free Run jumper is not installed, the clock outputs will stop after two full periods with no incoming clock pulses. That is, if the incoming clock has pulses every second to denote a measure, then the SCM Plus will stop outputting clocks if two measures (two seconds) pass without a clock. Thus there always will be a two measure delay from when the incoming clock stops to when the SCM Plus stops when the Free Run jumper is not installed. If this lag is an issue, send a trigger into the Mute jack whenever the upstream clock stops.
Updating Firmware
The SCM Plus firmware can be updated by playing a special audio file into the
PW jack.
When a firmware update is available, it will be posted on 4mscompany.com as a
WAV file (or zipped WAV file).
- Download the audio firmware file and prepare to play it on your computer or mobile device.
- Set the volume to maximum, both in the system/OS controls and also in the audio player application.
- Power off the SCM Plus and unpatched all cables.
- Patch x1 to Resync.
- Patch the computer/device output to the PW jack (any mono or stereo cable will work).
- Turn the PW knob to approximately 11:00 (a little bit counter-clockwise of center).
- Note: If you have a 4ms Listen IO or other module that boosts line level to Eurorack level, run the audio through it before patching into the PW jack. Set the PW knob to 0 in this case.
- Power on the SCM Plus.
- The module should boot into bootloader mode, with the In light blinking steadily.
- Begin playing the audio firmware file. You can monitor the signal by listening to the x8 jack.
- If the update fails, all the lights will flash rapidly. Adjust the PW knob and then press 4x Fast once to try again.
- If you are not using a line-to-Eurorack module, you may have to adjust PW and retry a few times before successfully updating the firmware. Typical PW knob positions range from 9:00 to 11:30. Try a few positions until it works.
- When the update succeeds, the lights will blink in order, one at a time (slow chase sequence).
Troubleshooting
- Make sure the volume on your device and app are at 100%.
- Try a different computer or device.
- Do not use sophisticated playback software such as Ableton, as these can inadvertently alter the encoded audio. Use the most basic playback program available.
- If you have an oscilloscope or a way to view waveforms, compare the output of the x8 jack with the output of the computer or device. Adjust the PW knob until the pulses are similar (accounting for 10µs – 75µs of latency).
- Use a line-to-Eurorack conversion module such as the Listen IO, setting the PW knob to 0.
LED Dimmer Trimpot
On the rear of the module is a small trimpot which can be used to set the LED brightness. Use a tiny Philips head screwdriver (#2) to carefully adjust the trimpot. Do not use excessive force or a screwdriver that doesn’t fit, or the trimpot could be damaged.
Clock Bus Jumper
Clock Bus is a 1:1 clock that runs along the gate pin of the Eurorack power
bus. This feature allows for a compatible module to send a clock signal over
the power bus, and for one or more modules to synchronize to this clock. The
MiniPEG, DLD, and QCD from 4ms are all capable of sending a clock over the
Clock Bus. Modules from other manufacturers that send Clock Bus are also
likely to be compatible, such as the Malekko Varigate 8+.
On the rear of the SCM Plus is a jumper to enable receiving clocks over the
Clock Bus. When this jumper is installed, clock pulses on the Clock Bus will
be sent to the In jack as if they were patched directly into the jack. When a
cable is plugged into the In jack, the Clock Bus signal will be ignored.
Multiply-by Amounts at Each Jack
Electrical and Mechanical Specifications
- 12HP Eurorack format module
- 0.95” (24mm) maximum depth (includes power cable)
- 16-pin Eurorack power header
- Power consumption
- +12V: 52mA max
- -12V: 15mA
- Clock Input
- 2.5V threshold
- 40kHz maximum
- Clock Outputs
- 12V gate outputs, rise/fall time approximately 1us
- 40kHz maximum
- Jitter (x1 output): max 30µs < 120BPM, max 5µs >= 120BPM
- Latency (clock in to x1 output): 8µs worst-case, 3.5µs typical
- CV Inputs:
- Rotate, Slip: Knob attenuates jack signal. Full range: 0V to +3.3V
- Shuffle, Skip, PW: Knob offsets jack signal. Full range: -5V to +5V
- Gate Inputs:
- 4x Fast, Mute: 2.5V threshold. Button toggles state.