18. How can multiple segments be looped?
Multiple DH_EnvSeg
segments can be looped using a Feedback (delayed) module. The following model
has been adapted, with permission, from a demo .se1 by Skye Klein. I've greatly
simplified the model to focus on the specific techniques used to achieve
multi-segment looping. Any mistakes are mine, not Skye's.
In the diagrams that follow, Envelope Out, Release Gate,
Duration, and End
Level connections that are not specifically related to the looping mechanism
have been removed to reduce clutter. Also, of course, most multi-segment loops
will have more than just the 2 looped segments shown here, but only 2 (the first
and the last) are needed
to see how it works.
Getting multiple segments to loop essentially
involves solving 2 problems: how to retrigger the loop, and how to avoid an
abrupt level change at the loop point.
The first is the need to retrigger the first
segment of the loop when the last looped segment has completed. This requires
routing the Gate Out signal from the last segment in the loop (Loop Seg2 in the
diagram below) back to the Gate In of the loop's first segment (Loop Seg1
below). Because of SynthEdit's limitation on feedback, this connection has to go
through a Feedback (delayed) module. In the example below, an incoming gate
signal is used to control a 1->Many switch through a Voltage To List converter.
As long as the incoming gate signal is high, Loop Seg2's Gate Out is routed
through the Feedback (delayed) back to Loop Seg1's Gate In to retrigger the loop.
When the incoming gate signal drops, Loop Seg2's Gate Out is switched to the
Release segment's Gate In, and the looping ends.
The second problem that has to be solved is how to pass the Level Out from
the segment at the end of the loop back to the beginning segment's Start Level
so that the loop transition will be smooth. The method diagrammed below does
this cleverly, avoiding the need for feedback. This is possible because the loop
will only occur if Loop Seg2 runs to completion, and at that point, its Level
Out value will equal its End Level input, which can be taken directly from the
Seg2 End Lvl slider.
There is a timing issue that must be dealt with,
however. The first time the envelope is triggered, before it begins looping,
Loop Seg1's Start Level must come from the segment before it, in this case, the
Attack segment. After that, it needs to come from Seg2's End Level. Thus, we
need to have the Many->1 switch set to "Attack Lvl Out" for the first pass
through Loop Seg1, and to "Seg2 End Lvl" for all subsequent passes.
This is accomplished by using a Monostable module
to generate a pulse of the same duration as Loop Seg1's first pass*. As soon as
the Attack segment ends, its Gate Out triggers the Monostable, and the input to
the Voltage To List goes high, selecting the Attack Level Out and sending it to
Loop Seg1's Start Level. The pulse ends at the end of the first pass through
Loop Seg1, dropping the input to the Voltage to List to 0, which switches the
switch to the Loop Seg2's End Level position for subsequent passes.
(*Note: Some time conversions were necessary because the Monostable's Pulse
Length is on a linear scale of 10 volts = 1 second, while DH_EnvSeg's Duration input
uses the same time cent scale used by SE's ADSR. The value on the Seg1 Duration
slider above is in milliseconds. It is multiplied by 0.01
to convert from milliseconds to tenths of seconds for input to the Monostable Pulse
Length. A DH_msToVoltage converts the milliseconds to volts on the time cent
scale for Loop Seg1's Duration pin.)
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