There’s been a need for a smaller MIDI connector, and now we have one
As electronic music-making devices continue to shrink, it’s no longer possible to include a 5-pin DIN connector in something that may not be much larger than a smartphone. A lot of companies have addressed the problem by using 2.5 mm or 3.5 mm TRS (tip-ring-sleeve) connectors because MIDI requires only three leads, but there was no standard, so there was no guarantee of compatibility with devices using TRS connectors.
Thankfully, the MIDI Manufacturers Association has adopted and released a specification that defines MIDI over TRS connectors. The tip connects to pin 5 on a 5-pin DIN connector, the ring connects to pin 4, and the sleeve (ground) connects to pin 2. This means you can create adapter cables easily to connect devices with 5-pin DIN connectors (like audio interfaces and controllers) to the new breed of mini-devices that use TRS connectors. As with standard MIDI cables, shielded, twisted-pair wires are specified as the conductors.
For more details, go to the blog post about the new specification. To download the specification for free, sign up to The MIDI Association (it’s free, they don’t spam you, and there’s a lot of good info).