I remembered looking at the Rise and Fall gate outputs on After Later Audio Tilt and Joranalogue Contour 1 slewing modules and finding unexpected behaviors. Recently I remarked about this on Modwiggler and was asked for details. So today I did this investigation.

Scope pictures tell the best story here. In all of shots below, the top (green) trace shows the input to the module, sometimes a gate and sometimes a signal to the input. The blue trace shows the output of the module. Red trace is the Rising Gate output and Yellow the Falling Gate output.

After Later Audio TILT

TILT is a favorite of mine. I have two of them which I use frequently. I use the Rise and Fall gate outputs without much thought. But they have some weird behaviors.

Above we see a typical bipolar gate going to the TILT Gate In. The toggle switch is in the middle position, Slew mode. Sustain knob is all the way down (no sustain). Both shape knobs are centered. Rise and Fall knobs are set so the envelope competes before the next rising gate arrives. Here we see the Rise and Fall Gate outputs working normally.

The only difference here is that the Sustain was turned up. The output behaves as expected, with the voltage sustaining until the gate drops. But the Rise and Fall Gates become chaotic during the sustain portion.

Above a sine wave about 0 to +4V is patched to the TILT input. The rise and fall slew rates are set at a medium rate so the output can follow this input. What are the Rise and Fall Gate output doing? They don’t even look like gates.

Here the slew rates are lowered, so that the sine is turned into a triangle. Now the Rise and Fall Gate outs seem to be working, but with a bit of trapezoidal shape.

If the rise and fall slew rates are sped up, so that the output can precisely follow the input, then we see no Rise or Fall Gates at all.

Again the slew rate is set medium, so the output can follow the input. Now the Rise and Fall Gate outputs are behaving sort of as expected, but the gates are spiky and noisy.

So much for the TILT. On to the Contour 1.

Joranalogue Contour 1

The Contour 1 is another unique approach to the universal slew. There is some overlap in features with TILT, including Rise and Fall Gate outputs. Let’s have a look

Above we see a bipolar gate being transformed into a bipolar trapezoid by the Contour 1. The Rise and Fall Gate outputs behave as expected, going high (5V) during the rising and falling of the outputs.

Above, Contour 1 follows a unipolar input with the slew rates set medium. At this slew rate (and faster slew rates) there is no output from the Rise and Fall gates.

Similar to what we saw with TILT, lowering the slew rate to where we observe an effect at the output results in the production of Rise and Fall Gate outputs.

Above, Contour 1 is following a bipolar triangle wave at a medium slew rate. Now here is something unexpected again. The Rise and Fall gates go high at the start of rising and falling, but they don’t persist until the end of rise or end of fall. They’re not keeping their contract!

Here, again at a slew rate a bit slower than the incoming voltage change rate, Contour 1 is lightly slewing the output. The Rise and Fall gates make an attempt to say when the output is rising or falling, but are again somewhat pulse like.

With an even slower slew rate Contour 1 does a better job of detecting when the output is rising and falling. The Rise and Fall gates look as we’d expect.

Conclusions

If your slew generator sports Rising and Falling gate outputs, check out what they do under different conditions. ALA TILT can misbehave by putting out glitches when slewing an external input. It also misbehaves when invoking the sustain feature with a gate on the gate input. Joranalogue Contour 1 acts better by not glitching, but under some conditions the rise and fall gates don’t reflect what the output is doing.

I found that on both modules the Rise and Fall gates work when some slewing effect is occurring. When the slew rates are turned faster, these gates give up and produce no output.

To be sure, when self-cycling, TILT and Contour 1 Rise and Fall gates perform as expected. It’s when gated to start an envelope or when slewing a signal on the input that the Rise and Fall gates can’t be fully counted on.