Event CHOP

From TouchDesigner 099 Wiki


The Event CHOP manages the birth and life of overlapping events triggered by devices like a MIDI keyboard. It can be seen as a simple particle system designed for MIDI keyboards.

The Event CHOP generates one sample for each off-to-on event in the input channels, which would often come from a MIDI In CHOP, MIDI In Map CHOP, Keyboard In CHOP, or python events sent to the Event CHOP. The sample exists for the duration of the event's attack+decay+sustain+release time.

NOTE: See the examples in Help->OP Snippets

The Event CHOP can used to follow a polyphonic music keyboard with MIDI velocity, and can generate generating one object, polygon or geometry instance for each event. It assures the object, polygon or instance exists until the event ends after an attack-decay-sustain-release phase. The Event CHOP is often fed through other OPs to the Instance parameters of a Geometry component.

The Event CHOP outputs up to 8 channels, with one sample generated per off-to-on event that is active. The sample is active until the attack-decay-sustain-release is over, at which moment the sample disappears (like particle death).

Watch the channel graph of the Event CHOP to understand what it is doing. It can be sent to a Limit SOP or a Channel SOP to place geometry for each event. You can send event information to the SOP via the Event CHOP channels that get transformed into geometry channels like tx, ty, scale, texture v (giving movie time offsets), alpha, r, g and b colors.

On a MIDI keyboard, you can trigger many events simultaneously, and, like particles, you may want to launch objects that remain in existence the next time you press the same key.

The Event CHOP is designed to handle this. It creates one sample every time you press any key, and that sample lives for any length of time. This CHOP is lightweight - the minimum number of channels and samples are created, even with 88-key MIDI keyboards and lots of pounding on the keyboard.

There are channels that represent age, note number and MIDI velocity when you pressed the key, as well as a flag telling if the key has since been released.

Each event has a unique ID, held in the id channel that can be used to generate random XY displacements of each note, for example.

A movie index is set by the state channel which rises from 0 to 1 and loops between 1 to 2 continuously until the note goes into its release state at which time it goes from 2 to 3. So for a bird cycle, you use the 0 to 1 state for the jump phase, 1 to 2 for the flappin in flight phase, and 2 to 3 for the landing phase.

The Event CHOP's 1st input is for event triggers.

The 2nd input resets the triggers.

The 3rd input is optional and allows for sampling values for each event.

See also: Timer CHOP, Count CHOP, Speed CHOP, Trigger CHOP

PythonIcon.png eventCHOP_Class

Parameters - Channels Page

The Event CHOP outputs seven channels that define the properties of the events.

  • id - The sequence # of the event, starting from 0 and incrementing by 1 for each event.
  • index - The channel index of the incoming CHOP that caused the event.
  • onoff - On while the event's button is on, 0 thereafter.
  • input - The value of the input channel when the input went on (at the birth of the event). It is often the note velocity value. If you pass the Midi In CHOP into the Event CHOP, and set the Midi In option to output the velocity, velocity will end up in this channel and preserved until the event ends.
  • time - Time in seconds from the start of the event.
  • adsr - The value according to the Attack, Decay, Sustain, Release. It uses the parameters on the ADSR page, regulating the speed and values, with extended parameters: Attack Time, Attack Level, Decay Time, Sustain Time, Sustain Min, Sustain Max, Release Time, Release Level.
  • state - This is good for playing back movies. You divide your movie into 4 parts that correspond to the (0=attack, 1=decay, 2=sustain, 3=release) phases. The state channel outputs fractional values, so you can watch it climb through all the transitions, including multiple sustain-sections. e.g., 0...1...2...2...2...2...3...4. If your movie is 8 seconds long, take the state channel and multiply by 2, passing it as the time-index of the movie.
  • state - Goes from 0 to 1 during the attack phase, 1 to 2 as it repeats in the sustain phase, and 2 to 3 in the release phase. It is suitable for indexing movies.

Reset Condition - Determines the reset behavior of using the 2nd Input Reset Trigger. This parameter is only active if there is an input connected to the CHOP's 2nd input.

Reset - Resets the CHOP clearing all events.

Parameters - ADSR Page

Attack Time - Affects adsr and state channel. Time to rise to max attack level.

Attack Level - Affects adsr channel. Peak attack level.

Decay Time - Affects adsr channel and state channel. Time after peak to sustain level.

Sustain Time - Affects adsr channel.

Sustain Min - Affects adsr channel. Level at start of sustain time.

Sustain Max - Affects adsr channel. Level at end of sustain time.

Release Time - Affects adsr and state channels.

Release Level - Affects adsr channel. Level at end of life cycle.

Speed - Affects the speed of the event, letting you stretch out or shorten the life of an event.

Global Speed -

Standard Options and Local Variables