Overview
TRS MIDI connections are getting more popular in MIDI devices , whether it's 2.5mm, 3.5mm or 6.35mm TRS jacks, presumably because of the smaller form factor as compared to the DIN5 MIDI ports, and the easier availability of TRS cables (or stereo cables) as compared to 5PIN MIDI cables. MIDI hardware devices are also getting smaller, which makes it more difficult to use the DIN5 connectors.
Although the MIDI Association adopted the Type A connection as the MIDI standard, many other variations still exists.
In this post, we'll go through the different TRS MIDI implementations used out there and what to do if you do not have the appropriate connection.
DIN MIDI Connector
In the good old DIN5 MIDI Connectors, 3 out of the 5 pins are used. Pin 2 is used as GROUND, Pin 4 is used as the current SOURCE, while Pin 5 is used as the current SINK.
What does SOURCE and SINK mean?
I'll do my best not to get too technical here. MIDI is really just 1s and 0s traveling over a wire and gets interpreted into meaningful data when received. The SOURCE provides the power, whether 3.3v or 5v, to power an LED in the optocoupler in the receiving device, while the SINK pulls that power to ground whenever there is data to be transmitted.
Optocoupler?
The optocoupler just acts as an isolator between the MIDI sender and MIDI receiver to prevent ground loops. This 1s and 0s gets transmitted via light so the MIDI sender and MIDI receiver are not electronically connected. In the MIDI standard, the optocoupler resides in the receiving device.
Some TRS MIDI devices exclude these optocouplers so that they can implement more functions in one port, like an expression input + MIDI port. You may face ground loop noise when using such devices with MIDI. More info here.
What MIDI messages looks like
Here's what a PC#10 Channel 1 MIDI message looks like on the oscilloscope. This movement of voltages from high to low at specific timings gets interpreted into meaningful (MIDI) data by the receiving device.
Types of TRS MIDI
So for a 5 PIN connecter to connect to a TRS connector, there has to be some sort of standard for every manufacturer to follow to ensure compatibility. However, before the TRS TRS MIDI specifications was published, manufacturers used their own specifications for their devices, which led to the various types of TRS MIDI connections we have now.
Type A
The Type A TRS connection is the official standard adopted by the MIDI Association. The Tip is the Sink (pulls the data line down) and the Ring is the Source.
Type B
Similar to Type A, but the Tip and Ring positions are swapped. The Ring is the Sink and the Tip is the Source.
Ring Active
Predominantly a Chase Bliss MIDI implementation. This is similar to Type B, but the tip needs to be left floating (not connected to anything, or in engineer's speak, left in a high impedance mode) to avoid interfering with any other function. The Tip needs to be left unconnected as it might interfere with the pedal's function if there is a voltage connected.
Tip Active
This is similar to Type A, but the Ring is left floating.
Predominantly a Meris MIDI implementation. Meris pedals send MIDI data back on the Ring connection. IIRC, we have encountered some glitches when we connected Meris with a Type A connection, which means that the Ring was powered. I have not been able to replicate that problem though.
What TRS to 5 PIN cables should I buy?
When purchasing TRS to 5 PIN MIDI cables, DO NOT purchase those specified as for Audio, as those are connected differently and will not work at all with your MIDI devices. If they state "for MIDI and AUDIO", do not buy those as well as they very likely will not work.
Look for cables that are specified as TYPE A or TYPE B, depending on what you need.
Type A adaptors are also available in our webstore at a great price.
How to connect a Type A MIDI port to a Type B MIDI port
If you have a Type A MIDI OUT port that you want to connect to a Type B MIDI IN port, the only solution (apart from getting a separate MIDI Box that can switch Tip and Ring signals) would be to re-wire your TRS cable where the Tip on one end is connected to the Ring on the other end, and the Ring connected to Tip.
If you are using the Omniport on our MIDI controllers, you can simply just switch between Type A, Type B, Tip Active or Ring Active connections in the controller.
That's it!
I hope that helped you understand more about TRS MIDI and how MIDI is transmitted. If you have any questions regarding this, just create a thread in our forum and we'll pick it up from there!
Keep making awesome music!
The Morningstar Engineering team