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CALIBRATING THE VPM-1
We made a video to illustrate the following procedure, which you can find on our YouTube channel,
in the VPM-1 playlist.
One of the things that makes the VPM-1 very versatile is the ability to set the active range (or sweep)
of the treadle to a position that is most comfortable for you. This means that you can set the minimum
volume position and maximum volume position anywhere along the pedal’s range of movement. Any
point below the minimum-volume position will be zero volume, and anything above the maximum-
volume point will be maximum volume. Calibrating the VPM-1 is the process of setting these two points,
plus three equidistant points in between. Since these five points are stored in the microcontroller’s
memory, calibrating the VPM-1 is only necessary once; but you may want to experiment with different
sweep distances and placements to find what works best for you.
The five calibration points must be equally spaced across the desired range of treadle movement in
order to produce the best volume linearity. The microcontroller will then manipulate these five points
in different ways to create the four other available tapers. To help with this calibration procedure,
we have included a “calibration card.” The front of this card provides a colorful variety of ranges of
treadle movement to choose from. On the back is something like a protractor. You might use this figure
to lay out a custom sweep by choosing your own five points (just make sure they are equally spaced).
If this whole idea is a bit confusing to you, never fear! Just watch the video, follow the instructions,
calibrate your pedal, and mess around with it for a while. Experiment with a few different sweep
ranges until you are happy with the action. It is easy and hurts nothing to calibrate the VPM-1 again
and again.
In this example (as in the video),we will use the calibration points shown in red on the card.
1. Set the treadle position where you want the minimum volume point to be. We have found that
what typically works best is to move the treadle until the gap at the back is about ½ inch (12mm)
(183,184). If you use the pedal’s fully-open position for minimum volume, then depending on the
variations in your pedal build, the minimum volume may not get all the way down to zero.
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