The MIDI (Musical Instrument Digital Interface) is the RS232 of the musical world, a serial channel interface that allows musical instruments such as keyboards, synthesizers, drum machines, computers, and other MIDI compatible devices to communicate with each other. A PC or keyboard can issue note commands that will initiate a connected synthesizer or drum machine to produce sounds. However, MIDI has its downside, much like RS232: if something doesn’t work, it is difficult to find out why. I invented the InLine MIDI Monitor to quickly diagnose problems unique to the MIDI environment. It looks like a cable that plugs into a MIDI port and displays the status of the line. The device can be battery powered for quick debugging while on the road, or run from a wall transformer to provide continuous MIDI line monitoring during a performance.

I am an amateur classical pianist and synthesizer player. I have a MIDI compatible piano and MIDI compatible synthesizer equipment. Occasionally I perform, and when I do, my biggest nightmare is beginning a solo performance by playing a dramatic opening chord—and not a sound is heard, except for the big clunk of the synth keys, and the bigger clunk in my heart. All too often, a cheap MIDI cable prevents data from getting from the keyboard to the rackmount synthesizer box. What’s worse is that I will have to check many things before determining what is the culprit: an incorrect channel setting of the keyboard or synth, an amplifier or mixer line cable that didn’t get plugged in, or—a bad MIDI cable. The MIDI protocol allows every note or other command to be assigned to one of 16 channels, so if there is a channel mismatch between the keyboard and the synth, no sound will occur. What a nightmare, a lot of things to have to remember under the pressure of a performance! Wouldn’t it be nice if I could be reassured that the connections were all working so I could concentrate on the performance? You bet, and that’s why I designed the InLine MIDI Monitor—an unobtrusive, battery powered (wall transformer is optional) 87LPC762 (Philips 8051 derivative) powered MIDI monitor that provides visual information about the MIDI connection.

The InLine MIDI Monitor checks for several things that can go wrong, and provides its status on a small 5x7 LED array (even though an LCD (Liquid Crystal Display) would be lower power, they are bad news for a performing environment. LEDs are much better for dark environments, for example in the back of a rackmount tower). The MIDI Monitor checks for receiver connectivity, active messages, channel information, and note integrity/noise. Since MIDI is a current loop, if the receiving end of the cable is not properly connected, it is easy to detect—this verifies that the rackmount synthesizer is actually present (cable is connected). That doesn’t sound like a big deal, does it? However, unless you’ve done time as a band roadie, you may not know what a rat’s nest of cables are involved in a instrument setup, and might not realize how easy it is to leave some cables unconnected or connected to the wrong device. It’s very nice to have a way to check that each end of a cable is properly connected.

The MIDI Monitor will also check for channel settings. This is one of the most common goofs in making sure that MIDI instruments are talking to each other. I will set the keyboard to transmit on channels 0 and 1, but set the synthesizer to receive on channels 1 and 2! Guess what happens when I play the keyboard for channel 0—nothing! If I’m lucky, I will figure it out quick, hunt down the MIDI channel configuration for both the keyboard and the synth and set them to match. But I really do NOT want to try to figure this out just before a performance. The MIDI Monitor comes to the rescue and will display in slow sequence the active channels on the line, thus allowing me to verify that the transmitting device (in this case, the keyboard) is functioning and what channels it is sending on. It will also watch for the MIDI active messages that are sent periodically, and display an idle status (IDL) if no keyboard activity is occurring (it displays IA inactive status if there are no MIDI active messages at all). I actually haven’t had this happen where a keyboard went dead on me, but this just provides reassurance that the keyboard is alive and waiting for me to play.

In the future, the MIDI Monitor will check for several other error conditions, such as note-ons without a corresponding note-off. This is an occasional problem that usually results from a noisy MIDI environment. In this case , the MIDI instrument was told to start the sound, but didn’t get the MIDI message that said to turn it off, which can be a very embarrassing thing to happen in a performance! It’s kind of like having microphone feedback

With such a powerful tool checking the MIDI cable connection, I can rest easy and concentrate on the performance!

DIAGRAM