SRAM (Static Random-Access Memory). Three other
microcontrollers handle the user interface, foot-switch
control, and metronome. All microcontroller software is
written in C, using Microchip’s MPLAB IDE (integrated
development environment) and the XC8 compiler.
How It Works — Plug and
The Box simply interfaces to any MIDI compatible
keyboard instrument via two MIDI cables in a loop-back
configuration. This is shown in Figure 4.
Keyboard instruments have a keyboard controller
and tone generator inside. The keyboard controller
recognizes all user input via the keys, buttons, sliders, and
so forth, then sends the relevant MIDI messages to the
tone generator which creates the sounds. This is called
local control and is usually a setting accessible via the
keyboard’s configuration screen.
Local control must be turned off when the Box is
used. The Box receives MIDI messages from the keyboard
(keyboard controller) and sends messages back (to the
tone generator). The flexibility of MIDI means you are
not limited to using the internal tone generator and can
connect to other sound modules or keyboards if you wish.
With a set list of songs loaded on the Box, you tap a
foot-switch to configure the keyboard for a song. Another
click, and the Box plays a section of recorded backing to
accompany your real time performance. A ‘Life on Mars’
example MP3 is available with the article downloads and
has been recorded on the Box. The piano track can be
muted, and the strings used as backing.
The Box has a Performance mode (Box on the floor)
and an Edit mode (Box on the desktop or keyboard-top).
Editing is via buttons and performing is via foot-switches. In
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; FIGURE 3. Opening the Box.
MIDI — The Enabler that’s Taken for Granted
It’s likely you have heard of MIDI (Musical Instrument
Digital Interface). It lets musical and computing devices
communicate in a common language, and has existed
since the 1980s. However, it seems there is little
acknowledgement or reflection on what a profound
‘enabler’ MIDI has been.
It’s staggering what MIDI has done for music. Any
post- 70’s pop song is likely to have involved MIDI. Music
‘sequencers’ which tie all the tracks of a song together all
use it. Almost all musical keyboards and devices have MIDI
sockets that let them talk to each other.
The underlying concept of a ‘common language’ is so
powerful. Human evolution exploded because of it. This
project wouldn’t be possible without it. When the first,
beautiful, musical score of a recording effortlessly ‘fell out’
of the MIDI Replay Box via a sequencer, it seemed like a
‘free lunch’ — too good to be true!
MIDI is also profound in that it’s about the ‘control’
of music rather than the ‘audio’ itself. It’s like recording
the actions of the musicians rather than the sound they
produce. That’s clever: You can edit notes, durations,
tempo, transpose, even instruments used — all without
having to re-record anything! Plus the storage of ‘actions’
is tiny compared to recording audio.
; FIGURE 4. How the Box is used.
September/October 2018 27