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The signal produced by our piezo must be filtered so the module can detect position from this signal. Practical considerations for the DIYer The cleaner the piezo signal, the more effective the detection of the position. Even if a piezo is a bad microphone, we can help it to co-operate with a module. Like a guitar, shielding the wire to which our piezo is attached will reduce useless noise. If you do not use a shielded wire to connect your piezo to the trigger’s socket, interlacing both negative and positive wires can also help to get a cleaner signal. Roland triggers feature an inverse polarity, so it is usually a good idea to link the ceramic part of your piezo to the “sleeve” (ground) part of your jack socket, and the brass part of your piezo to the “tip” (positive) part of your jack socket. This way, the first half-wave produced by your piezo will be negative, which may be important in the context of the waveform analysis job performed by your module. Piezo transducers have different properties and some may not get the exact frequencies a Roland module needs to detect the position of your hits. You’ll need to change a piezo for a different one if positional sensing does not work with it.
Positional sensing from the rim piezo As far as I know, Roland modules do not appear to work this way. Some may think it is implemented like that because some Roland modules are able to differentiate “open” and “shallow” rim shots. However, the rim piezo is usually used as a binary switch (rimshot or not rimshot). Velocity and position are always processed from the head piezo. Some non-Roland and many home-made modules or software add-ons may use a two-piezo position detection approach, probably because: • The first half-wave method needs the piezo signal to be filtered properly (extra filters and fine tuning needed). • Roland triggers are produced in series with the same type of piezo featuring specific properties (Roland module algorithms are made to work with Roland triggers) while home-made or other brand triggers may not provide the signal a Roland module expects to work with. • The first half-wave method is patented by Roland.