A Beginner's Guide To MIDI 7

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Don't All Talk At Once!

In the diagram on the previous page you'll notice I've shown the master keyboard with a cable attached to its M.I.D.I. In. This is required if the master keyboard is in fact a synthesiser with its own in built sounds rather than a dumb controller.
With the cable attached to the M.I.D.I. In the sequencer will be able to send instructions back to the master keyboard in order for it to generate its own sounds in response.
This causes a problem though.
If the keyboard isn't connected to any other M.I.D.I. devices, and a key is pressed on its keyboard, we want the key to cause the sound generator in the synthesiser to play the corresponding note. If this didn't happen then it wouldn't actually be possible to play the synthesiser as a stand-alone instrument, which of course it is.
When the keyboard is connected to the computer, the sequencer programme will re-transmit the received information, which will eventually be received back at the synthesiser's M.I.D.I. In.
In short, the synthesiser will be receiving instructions from two places at once. This can result in two identical notes being played using the same sound, or if the targets for the two instructions are different, then unwanted sounds may play inappropriate parts. Either result halves the polyphony.
Just in case the problem isn't quite clear, here's a diagram which may help:

There are is a solution to this problem. In fact there is more than one, but I'll only look at the best, which breaks the connection between the sound generating part of the synthesiser and the keyboard. This is acheived by turning Local Off on the synthesiser. This may be easy or difficult depending on the complexity of the synthesiser concerned. The Alesis Quadrasyth for instance has a reference to Local Off in its manual, but the controls used to acheive it aren't called by that name, and are rather confusing. On the other hand the Kawai KC20 has a simple page where Local can be turned on or off.

Of course, leaving Local Off makes things simpler when working with a sequencer, but you'll need to remember to turn it back on again when you use the synthesiser as a stand-alone instrument. If you find the keyboard doesn't generate any sound in this situation, its probably worth checking that Local has been turned back on.