This post discusses scope trace pics of New Systems Instruments Inertia, in the Low rate mode. The Low rate mode is useful for envelopes, LFO, and slew limiting.
Attack-Decay Envelope
INTERFACE: Rise/Fall
Fall Momentum: all the way down (CCW); other pots centered
A short pulse is sent to the TRIG input every 1.124 seconds.
Scope shows 1st Order out in yellow; 2nd Order out in blue. 1st Order Max is 4.96V, Min is 80mV. 2nd Order Max is 3.36V, Min is 240mV. 2nd Order lags the 1st Order, has a smoother shape and a smaller amplitude.
The next pic has mostly the same settings, except Rise is set to the maximum (CW). Looks like a very “snappy” envelope. 1st and 2nd Order outs are the same amplitudes, Max is 4.96V and Min is 80mV. The 2nd Order lag is negligible, but the shape is different.
The third A-D pic shows Fall time set to maximum (CW), and we’ve dialed a longer Rise time. The 1st Order amplitude remains the same, but the 2nd order amplitude here is smaller: Min -90mV, Max +2.56V, and the shape is different.
Attack-Release-Sustain-Release Envelope
INTERFACE: Rise/Fall
Fall Momentum: all the way down (CCW); other pots centered
A 0 to 4.8V square wave is sent to the Input.
Here the scope shows the 1st Order output in yellow and the square wave input in blue. With Rise Momentum centered there is some overshoot, so the max out is 5.44V. The output then falls at the fall rate and levels off at the 4.8V level of the square wave, before releasing when the square wave falls.
For the next pic, we turned the Rise Momentum pot to about 3 o’clock. Now there’s a higher overshoot, to 7.2V, before falling in a wobbly manner back to the 4.8V height of the input.
Next, we turned Rise Momentum full down (CCW). And now we see no overshoot at all, and in fact the maximum levels out at 4.48V, which is lower than the square wave input. (I wonder why.) This setting would be good to make a standard Attack-Release envelope that stays high while the input gate is high. Rise and Fall times are of course adjustable and controllable by CV as well.
Slewing a Square Wave
INTERFACE: Rise/Fall
All pots are centered.
A bipolar square wave (-4.6 to +4.8 volts) is sent to the Input. The scope vertical range is now 5V/division. With equal rise and fall momentum there are small overshoots both top and bottom.
Next, we increased both Rise and Fall momentum pots to point at 3 o’clock. Damped sinusoidal waves now appear prominently on both top and bottom. These will of course be following the rise and fall rates (which are currently set at 12 noon, centered).
The third screen shot has the rise and fall momentum both turned up full. This is sort of like an LFO, but with the output biasing up and down, following the square wave.
Slewing summary: For normal slewing, you probably want to minimize both momentum settings. Otherwise, artificial sinusoidal waves will start showing up. But that’s a feature!
LFO
INTERFACE: SKEW
Momentum Skew is full up (CW). Other pots are centered.
Here we are back to showing both 1st and 2nd Order outputs. The 1st Order output is a big sine wave, going from -6.8V to +6.0V. The 2nd Order output lags by 45 degrees and goes from -5.0 to +5.0V. The period is 676 ms.
Next one has Frequency Skew at the left-most setting (CCW). The wave shape now resembles a falling ramp wave. Skew is of course CV-able, affording CV wave shape. The 1st Order output is going -7.2V to +5.8V, and the period is a little longer, 688 ms. The 2nd Order out is now going -4.4V to +6.0V and has a different curve.
Finally we look at the Frequency skew full CW. The 1st Order out is going -6.6V to +6.4V, rising with a sine-like curve. The 2nd Order out is more linear, and going -6.2V to +4.2V. The period became a little shorter, 657 ms.
In summary, the LFO mode affords variable wave shaping that preserves the period pretty well, but shifts the output offsets and ranges a bit.
This post will be followed up by one that exercises Inertia in the High (audio rate) mode.
