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Probability Drum Trigger

Ochen K.

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The PDT2 is a two-channel probability step sequencer. It allows you to add the slightest bit of variety in a hi hat or shaker to a preexisting beat, or generate brand new, completely random drum tracks that continually surprise the ear.

Product details

(Current version 1.2.3 - see update notes below for details.)

Most drum step sequencers, including the Redrum Drum Computer, allow you to determine whether a sample will play at a particular step or not, but it is a binary choice - either the sample is triggered or it isn’t. A probability step sequencer allows you to determine whether a sample will play at a particular step, but also allows you to set the probability of the sample actually being triggered. For example, you can set step one to trigger sample one, but only 50 percent of the time. In the PDT2, when a step dial is set to 0 percent, the sample will never be triggered at that step. When the dial is set to 100 percent, the sample will always be triggered at that step. But when a step dial is set to somewhere in between 0 and 100 percent, the sample will be triggered that percentage of the time. (E.g. if a dial is set to 25 percent, the sample will be triggered, randomly, approximately 25 percent of the time at that step.)

Linear Drumming

A single PDT2 can control up to two drum tracks, either independently, or in tandem with each other. When the Linear Pattern button is turned off, the two sequencer channels operate completely independently. When the Linear Pattern button is turned on, each channel will calculate its own probabilities, but will never trigger at the same time as each other. For example, if channel 1 controls a closed hi hat sound and channel 2 controls an open hi hat sound, you might not want them to ever trigger at the same time. In that case, press the Linear Pattern button. Now, on any particular step, if both the closed hi hat and open hi hat channels are triggered, only one will play - usually the one with the higher probability.


When dealing with random numbers, you usually want completely random numbers. But when making music, you usually want control over the final sequence of sounds. The PDT2 gives you both. The random probabilities that the PDT2 generates are completely random based on a “seed” that you control. For any given pattern of dials, and any given position in the song, when the seed is the same, the triggers will be the same. This means that when you have your drum pattern dialed in, the resulting triggered beat will sound the same each time you play the song. If you change one of the step dials, the entire beat will change. But if your dials are exactly where you want them to be, and drums are triggered exactly as often you want them to be, but you just don’t like the particular random choices of the pattern, change the seed. You’ll get a whole new pattern based on your same set of probabilities. Because any change in any probability dial produces an entirely new random sequence, and the seed dial can produce random variants of each pattern of dials, the variations are nearly endless, yet you can have complete confidence in knowing ahead of time what the final triggered sequence will sound like.


When playing a groove, a live drummer will often shuffle a hi hat ride differently than a shuffle between the snare and bass drum, both of which might be different than the global shuffle of the song. Each PDT2 has its own independent shuffle dial.

CV Outs

Each PDT2 has two channels. Each channel has two CV outs on the back of the device. The first is a Gate CV output. This is the primary trigger. This is the CV that goes into the Redrum or Kong or any other instrument that you want triggered based on probabilities. The other CV output is a Level CV output. When a signal is sent out of the Gate CV, the value of the source probability is sent out of the Level CV. For example, if the dial for step one is set to 50 percent, and the PDT2 determines that it should be triggered, a signal is sent to the Gate CV to trigger the sample, and a value of 50 percent is sent to the Level CV. This Level CV can be used any way you wish. In the example Combinator patches provided with the PDT2, the Level CV is often used to control the volume of the triggered sample. The thinking is that if a step has a low probability, it might be a ghost note, or a pick up, or something otherwise ancillary to the beat. Most of the time, those elements are softer than the primary elements of a beat - the downbeat or back beat - which should be louder, and should be played more consistently, meaning a higher probability. Therefore, when using the Level CV to control volume, the higher probability triggers are louder and the lower probability triggers are softer. There is no requirement to use the Level CV in this way, or to use it at all. But when used in this way, it adds a level of complexity and listenability and interest to a beat.

If you have any questions or suggestions, send them to [email protected]

** 1.2.2 UPDATE **

1) Add automation to Gate, Steps, and Speed dials.

2) Changed the way gate length works. Now, a gate length of 100 percent is the length of four beats.

3) Fixed light persistence bug when changing pattern length.

4) Fixed bug where note lanes were automatically created when creating a new device. Now, note lanes are not created automatically, but can be created manually.

** 1.2.1 UPDATE **

Four new pieces of functionality have been added for the 1.2.1 release:

1) A Gate dial now controls the length of the trigger signal sent out of the Gate CV.

2) A Steps dial now determines the number of steps in the sequence pattern, from 1 to 32. (Steps beyond 16 wrap around to the beginning of the dial sequence.)

3) A Speed dial determines how fast, and at what resolution, the pattern plays - from each step lasting a half note, to each step lasting a 36th note. Triplets included.

4) A Seed In CV on the back of the PDT2. Hook an external LFO to the Seed In CV to make the PDT2 always random, every time you press play, even if you don’t change any dials.

** 1.2.3 UPDATE **

1) All parameters are now Remote enabled.



Released: 2013-03-27
Version: 1.2.3