Event CHOP

Summary

The Event CHOP manages the birth and life of overlapping events triggered by devices like a MIDI keyboard. It is 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 be coming from a MIDI In CHOP, MIDI In Map CHOP or a Keyboard CHOP. The Event CHOP is used to follow a polyphonic keyboard, like an 88-key music keyboard with velocity, generating one object or polygon for each event, and making sure the object or polygon exists until the event ends after an attack-decay-sustain-release phase. The Event CHOP is often fed to a Limit SOP, which generates one surface per sample.

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 is most frequently 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, used to generate random XZ displacements of each note.

The 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.

Parameters - Channels Page

Transpose Inputs - This option makes the CHOP look at the inputs as one key in each sample of the input. It does a Shuffle CHOP to the input before using it.

Channels

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.

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.

Time Dilate - Affects the life time of the event, letting you stretch out or shorten the life of an event.

Standard Options and Local Variables

None.