The MIDI Manufacturers Association (MMA) has published a Recommended Practice for the use of "TRS" connectors with MIDI devices. The document defines how to wire "tip-ring-sleeve" connectors and describes the necessary device circuitry and cable specifications to support MIDI 1.0 compliant electrical connections to DIN-MIDI devices. It is available now for download from www.midi.org.
The inclination towards smaller hardware devices has made it increasingly difficult to make use of DIN connectors for MIDI In/Out in the past few years. Many manufacturers have chosen to use 2.5mm or 3.5mm "TRS" connectors instead. But since there was no specification for wiring a TRS MIDI connection, the situation exists where two devices may not have chosen the same wiring scheme, so compatibility between devices is not known. By specifying the pin-out for the TRS connection, and also the connectors for the adapter cable, developers can ensure greater interoperability between TRS and DIN-MIDI equipped devices.
"Compactness is important to today's mobile musician, " says Gary Kerzner at IK Multimedia "and a recommended practice will mean they can choose devices from different manufacturers with confidence that they will communicate like MIDI devices are supposed to."
To download the "Specification for use of TRS Connectors with MIDI Devices" [RP-054], join the MIDI Association, the global community of people who work, play and create with MIDI at www.midi.org.