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The main thing to note about drum triggers is it is a compromise.
Drum modules were never designed to use splitters as modules reads the total voltage of an input and converts to a MIDI signal.
The head (Tip) is separate and the Rim (Ring) is separate..hit simultaneously the module still interprets as a single voltage signal.There are modules such as the Roland modules where the module takes the combine voltage reading between the Head and the Rim (when hit simultaneously)and interprets a different MIDI signal and selects the Rimshot sample.Splitters for Roland modules require a 100k resistor.
Single cable Triple zone cymbals work on a stereo TRS input because there is a resistor separating the signal between the bell switch and the edge switch...switches are not piezo's..they are tied to the piezo as open/close switches in a circuit with the amount of voltage sent determined by the velocity of the hit/voltage from the piezo.Ride cymbals have a dedicated input(s) in order to function properly.
Drum modules (most) that can't interpret the voltage of a simultaneous Head/Rim hit just cancel out as the module doesn't know how to translate that specific voltage to MIDI which selects/triggers the sample.
One thing I have never tried for an Alesis module .is a resistor on one side of the splitter to delay the signal on a simultaneous hit..more than likely it will just abruptly cut off (like a mute group) the sample that is playing.
The best way for splitting triggers is an additional TMI like the
eDRUMin ,
Trigger IO/
DDTI (The ddrum DDTI has been removed from their site so the licensing with Alesis must have expired.) or an additional module to the MIDI in on the STRIKE module.The downside to that is the Rim will still be active if using TRS cable.You
can use TS cables for the Toms and Snare (eliminate inadvertent triggering the rim)..you
cannot use TS cables for the Cymbal inputs.The ring is tied into the circuit and the input will not function..otherwise if using splitters select the triggers you split for instruments/triggers you would never hit simultaneously.
EDIT:Added links