The SP-404 has MIDI Input capability, but not Output unfortunately. I’ve chained four of my machines together, and because there is no MIDI Output on the SP-404 I must put it last. This also means that all of my other machines must possess both MIDI Input and Output.
Simply put, the MIDI Output from the very first machine in my chain acts as the master to the next machine that proceeds it in the MIDI chain. To continue with this analogy the responding machine is called the slave. In my current set up, my first machine is the Roland TR-8, which acts as master to the next machine in my chain which is the Roland S-1 synthesizer.
(I also feed the main 1/4″ outputs from the S-1 synthesizer into an “External Source” input on the TR-8, which allows other synchronizing features, such as a side-chaining effect – but this is not MIDI-related).
The S-1 synthesizer received MIDI input from the TR-8, making it the TR-8’s slave, however, the S-1 then acts as a master to the Roland TB-3, a bass sequencing machine. Lastly in my chain, the TB-3 acts as a master as it sends MIDI output to the Roland SP-404, a machine which can only act as a slave because it is not equipped to send MIDI output.
The paramount advantage to these MIDI signals being sent and received to and from machines is to synchronize their time clocks, or Beats Per Minute (BPM). Starting and stopping the master machine will trigger a synchronized start and stop to its slave machine. Also, increasing or decreasing the tempo or BPM of the master machine will automatically increase or decrease the BPM of the slave machine so that their tempos match and are being played in synchronization. Within the MIDI chain, it is not possible for me to adjust the BPM’s on any of my machines except for the first master, which for me is the Roland TR-8.
To trigger a start on my first master machine is to trigger each of the rest of the following machines to start at the same time. But if I trigger a start on my second machine, only the following machines within the MIDI chain will also start (ie: my 3rd and 4th machines). The first machine in the chain will not start because it does not receive commands from any of the other machines. So then if I start the 3rd machine, only the 4th will follow command. And if I start my 4th machine, only it will play, because it is not sending any commands to any machines.
If I want to have all machines running in synchronization, but I only want to hear from one or two of them at a time, I simply adjust their volume knobs accordingly, or if you are running your machines into channels on an onstage mixing board, and if the mixing board channels have Mute buttons, you can simply use the Mute button to silence machines audibly, while in actual fact they are still running through the loops in synchronization. So maybe I want to have all four machines running together, because I know that ultimately I will want to incorporate all of them into my song or rhythm, but for a specific part I might only want to hear the 3rd machine. If I stop either the 1st or 2nd machine, this will trigger the 3rd machine to stop (as well as the fourth), but I don’t want this. Also once I start the 3rd machine, its start will trigger the 4th machine to start, and I don’t want this either. I have found that running all machines all of the time and simply adjusting or muting their volumes as needed is the best way to overcome this situation.