gates_and_triggers.md

Gates and Triggers (G&T)

This program is inspired by the After Later Audio G&T module. The program converts a gate or trigger signal on din into a gate signal with a variable length and rising/falling edge triggers.

I/O Mapping

I/O	Usage
din	Incoming gate or trigger signal
ain	CV control over output gate length
b1	Manual input equivalent to din
b2	Manual toggle input
k1	Primary gate duration control
k2	Attenuator for CV input on ain
cv1	Gate output for din/b1
cv2	Trigger output for the rising edge of din/b1
cv3	Trigger output for the falling edge of din/b1
cv4	Trigger output for the falling edge of cv1
cv5	Toggle output; changes state on every incoming rising edge
cv6	Trigger output for the falling edge of cv5

Gate/trigger input on din should be at least 0.8V. Ideally the trigger duration should be at least 10ms, though shorter triggers may be usable.

ain expects an input range of 0-10V. k2 acts as an attenuator for this input signal.

The gate output on cv1 has a range of 50ms to 1s, depending on the position of k1. The knob response is quadratic, giving finer precision at the higher (clockwise) end.

When ain receives maximum voltage and k2 is set to maximum gain, the duration of the gate on cv1 is increased by 2 seconds, giving an absolute maximum gate duration of 3 seconds. The following formula gives the exact calculation of the gate duration:

k1 in range [0, 100]
k2 in range [0, 1]
ain in range [0, 1]
MAX_GATE = 1s
MIN_GATE = 50ms

q(x) = (MAX_GATE - MIN_GATE) / 10 * sqrt(x) + MIN_GATE

t = max(
    MIN_GATE,
    q(k1) + k2 * ain * 2s
)

Gate time is rounded to the nearest millisecond.

Fine-tuning Gate Duration

k1 offers fairly coarse control over the gate length of cv1, especially at low values. If you need to fine-tune a gate duration in the 50-150ms range you should set k1 to its minimum value and use a combination of a constant voltage into ain and a relatively low gain set on k2. By adjusting the value of your input voltage and turning k2 you should be able to fine-tune the gate duration much more accurately.

For example to accurately achieve 60ms gates, patch the output from an adjustable voltage source such as Intellijel's Quadratt (0-5V) or Molten Modular's Motion Meter (0-10V) into ain. Turn k1 to its minimum setting and leave it there. Slowly increase k2 and your voltage source while keeping an eye on EuroPi's display. When the display reads Gate: 60ms stop adjusting k2 and the input voltage. While fiddly, this method will provide much finer control for short gate durations.

Timing Diagram

The following diagram shows the input and output states of the module. The height of the input to din or b1 is irrelevant, as long as it is enough to trigger the rising-edge interrupt service handler on the module (approx. 0.8V minimum).

DIN or B1
         __________          __________
________|          |________|          |___________________
        .          .        .          .
B2      .          .        .          .
        .          .        .          .           __   _
__________________________________________________|  |_| |_
        .          .        .          .          .    .
        .          .        .          .          .    .
CV1     .          .        .          .          .    .
        .______    .        .__________________   .    .
________|      |____________|          .       |____________
        .  L1  .   .        .       L2 .       .  .    .
        .      .   .        .          .       .  .    .
CV2     .      .   .        .          .       .  .    .
        ._     .   .        ._         .       .  .    .
________| |_________________| |_____________________________
        .T     .   .        .T         .       .  .    .
        .      .   .        .          .       .  .    .
CV3     .      .   .        .          .       .  .    .
        .      .   ._       .          ._      .  .    .
___________________| |_________________| |_________________
        .      .    T       .           T      .  .    .
CV4     .      .            .                  .  .    .
        .      ._           .                  ._ .    .
_______________| |_____________________________| |_________
        .       T           .                   T .    .
CV5     .                   .                     .    .
        .___________________.                     .____.
________|                   |_____________________|    |___
                            .                          .
CV6                         .                          .
                            ._                         ._
____________________________| |________________________| |_
                             T                          T

We assume that between the first and second pulses, the combined CV input via k1, k2, and ain has changed, resulting in different gate lengths (L1 and L2, above). The trigger durations marked with T are 10ms.

Delayed Triggers

If you need a delayed trigger, cv4 can be used; set the gate duration of cv1 to the desired delay duration. cv4 will fire a 10ms trigger on the falling edge of cv1, which will correspond with the rising edge of din plus the delay. Note that using cv4 in this way will limit the usefulness of cv1 and cv3, as the gate length will be used to control the delay.

There is no way to add a delay between the signal received from din or b1 and the rising edge of the gate on cv1.