INTRODUCTION TO SYNTHESIZERS - hol.gr

By connecting a MIDI-keyboard to the sequencer, you can just play your parts, and let the sequencer record
and store your every move. The sequencer can then replay all the phrases and parts, exactly the same way as
you played them. The recorded data can also be overdubbed, edited and manipulated in almost any way you
like.
Today, dedicated hardwired MIDI sequencers have almost completely been replaced by computer software. We
shall look at these in the next chapter.
Local control
A keyboard synthesizer has two distinct parts: the keyboard itself and the synthesizer circuits inside the shell
that actually produce the sounds.
When played, the keyboard triggers the synthesizer circuits and sends out MIDI messages. But if we wish, we
can separate the keyboard from the sound generating circuits. This is called Local Control and can be set either
from an instrument's front panel or via an incoming MIDI message.
When the synthesizer is in "Local Control Off"-mode, the keyboard will continue to send out MIDI data when
played, but it no longer triggers sounds directly from its own synthesizer circuits. At the same time, the
synthesizer section will continue to respond to incoming MIDI messages while ignoring the attached keyboard.
The keyboard can send on one MIDI channel, while the synthesizer responds to another. This is especially useful
for MIDI recording work, when only the sequencer should be triggering the synthesizer while you record new
parts for other instruments in the studio.
The illustration below shows a typical MIDI setup. A master keyboard synthesizer is used to enter the MIDI data
for all parts into a sequencer. The sequencer in turn controls three slave synthesizers. All synthesizers are
connected in one MIDI chain, but they only respond to their specific MIDI channels and ignore everything else.
As you can see, the last synthesizer in the chain is the same keyboard you use to enter your parts. This synth is
now both used as a MIDI "keyboard" and a "sound module", and so it must be operating in "Local Off" mode.
Now, just for the experiment's sake, let's set the Local Control of the master synth to On. What happens now?
Well, as we play a key on the master keyboard, a note is generated. But the corresponding MIDI signal is also
sent into the sequencer, and echoed through all the three slave synths. Finally the signal will arrive back to the
master synth - which then of course will play the very same note one more time, just a fraction of a second
after the key depression. The result is a strange, doubled, "flanged" sound, most audible with short, staccatotype
of sounds, such as drum sounds. The polyphony of the master synth will also be halved, since each key
depression now triggers two sound circuits at once.
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