I am nuts about voltage-controlled slewing modules, which all stem from the Serge Positive and Negative Slews, and the Dual Universal Slope Generator (DUSG).  In Eurorack I have Make Noise Maths and Make Noise Function.  Some contenders include the Befaco Rampage and the WMD SSF Mini Slew.  I just received a Mini Slew and installed it next to the Function.  They are both the same size (8 hp).  Here’s my initial comparison.  Rather than make feature lists, I’m going to compare by function.

Inputs and Outputs

Both have an input for a signal to be slewed.  The output will follow the input, but the rate of change going positive or negative (rise and fall) are controlled by the module.  Outputs are handled differently on the two modules.  Function has a positive output, corresponding to +Out on the Mini Slew.  Function provides a full level inverted output as well.  Mini Slew includes an internal balanced modulator (VCA/Ring Mod) for processing the output.  It’s called Variable Output.  The Var Out knob acts like an attenuverter for this output.  This is very handy for reducing the 8 volts output in cycle mode when you want to control a module without CV attenuation.  Additionally, Variable Out has a CV input, so it can act as a VCA or Ring Modulator, depending on whether the CV is positive only (VCA) or swinging positive and negative.

Triggering and Cycling

Both have a trigger input that works the same way on both modules.  A positive trigger or gate will initiate one cycle of rise (to about +8 volts), followed by a fall back to zero.  If a new trigger is received before zero volts is reached, the output begins rising again.

Both have a cycle button with corresponding LED.  However Mini Slew includes a cycle gate input, like Maths.  Mini Slew remembers the cycle button setting over powering the module off and on.  Whereas Function always starts up cycling, which can be annoying.

A known oddity of Function (and I think Maths, too) is that when cycling, a pulse is output on the signal input.  Mini Slew doesn’t have this issue.

EOR and EOC

End-Of-Rise and End-Of-Cycle pulses are available on both modules.  As advertised, EOR goes high at the end of rise, i.e. at the start of fall, on both modules.  Likewise EOC goes high at the end of a cycle on both.  Both modules will cycle if EOC is patched to Trigger In.

But the point at which these pulses are low differs in the two modules.

On Function

EOR remains low when not cycling, goes high at the start of fall, and low at the end of fall.  That is, EOR is high only during fall.

EOC is exactly the inverse, low only during fall, sitting high when not cycling.

On Mini Slew

EOR remains high when not cycling and goes low at the start of rise.  That is, EOR is low only during rise.

EOC is not the inverse of EOR.  It goes low at the middle of rise, rather than at the start of fall.  It goes high at end of fall and remains high when not cycling.

So, on Mini Slew, both pulses are high when not cycling.  EOR goes low first, at the start of rise, followed by EOC in the middle of rise.  From the middle of rise to the start of fall, both pulses are low.  Then in turn EOR goes high at end of rise and EOC goes high at end of fall.  It’s more complicated than with Function.

Rise and Fall CV

Both modules have rise and fall knobs and CV inputs.  Function has a ‘Both’ CV input, which corresponds to the FM input on Mini Slew.  ‘Both’ and FM CV increase the frequency with more positive CV, with an exponential response.  (This is the 1V/Oct CV input on the DUSG.)  The response curves for Rise and Fall can be adjusted (more below).  Mini Slew adds a CV Sum mode, toggled by a button.  In this mode the Rise and Fall CV inputs are summed and applied to control both.

Shape

The response curve is adjustable by a knob on either module from Log through Linear to Exponential.  But Mini Slew goes farther. It has a switchable Time Compensation mode which greatly reduces the impact to the frequency/rate as the Shape is changed. With this off the behavior is the same as on Function, i.e. turning more Exponential will also increase the frequency.  Mini Slew adds CV over Shape, which Function doesn’t have.

Hang

Function has a Hang input, which acts like a track/hold.  A high gate here will freeze the output, where it will remain until Hang goes low.  Mini Slew doesn’t have this (nor does Maths).

Audio Oscillation

Both modules can go into audio rates.  I measured the maximum for Function is around 1.2K Hz, whereas Mini Slew can go up to about 620 Hz.  This is with the rate knobs all anti-clockwise and CV inputs maxed out.  At the maximum frequency, Shape has no effect on either module, and the wave form is a triangle.

Indicators

A big difference is that Mini Slew uses blue LEDs and Function has red and green. (I’m not keen on blue LEDs.) In addition to the Cycle LED, Mini Slew has indicators to show CV Sum mode and Time Compensation mode.  The same button selects these, a quick press for CV Sum and a long press for Time Compensation.  Function has a bi-color LED to indicate EOR/EOC, but Mini Slew does not have indicators for these outputs.

Another big difference is the output level indicator.  Function has a single bi-color LED, which is quite useful to show how far the output is going into negative voltage.  Mini Slew opted for a 6-LED graph (with a red one at the top).  It does not indicate the level of negative outputs.  I’m with Make Noise on the output indicators.

Summary

I’m wondering whether I will keep both of these, or maybe replace the Function with another Mini Slew.  I like to have two of the same module.  I don’t want two Functions.  I’m undecided at this time whether to replace the Function with a second Mini Slew.  Mini Slew has the edge with features, especially the Variable Output, and CV over Cycle and Shape.  Not surprising, given the higher cost ($199 USD) over Function ($165).  I don’t need the Hang input, since I have about a dozen sample and holds in the same rack already.  But I’m not sure I’m ready to be blinded by two rows of glaring blue LEDs!  Seems a small defect to put up with, though.