MIDI Drum Pad
A clever pad-to-MIDI converter takes some stick from Matt Isaacson. A blow-by-blow account.
WHAT DO YOU get when you divide a Roland Octapad into eight equal rectangles? In reality, you get a pile of rubble. But substituting a conceptual blade for a hacksaw blade, gives you eight Boss MPD4 MIDI Pads.
The MPD4 is a junior version of the Octapad, and owes much of its functional design to its big brother. Visually it more closely resembles the Boss Dr Pad, but the MPD4 is a MIDI-only device which generates no sound of its own. Instead, it sports all the essential features of a MIDI drum pad, and although it offers nothing in the way of note layering, auto-echoing or other esoteric MIDI functions, it does include a couple of performance features not found on the Octapad. Power comes from a single 9V battery or an AC adaptor (not included), making it an ideal companion to any battery-powered MIDI synth or rhythm box for playing "on location".
The playing surface breaks no new ground - a stiff metal plate covered in tough rubber and fixed to the top of the MPD4 box with a thin layer of softer foam rubber to provide stick bounce and a measure of mechanical isolation from the housing and its mount. This arrangement gives the pad an adequate if somewhat "stiff' playing feel.
The design of the MPD4 follows a basic approach: controls are minimal and no read-out is provided - save the edit mode status LED. Connect the MPD4's MIDI Out to the MIDI In on your whatever, turn both on, and start playing. If the MPD4 is connected to a late-model MIDI drum machine, you will probably hear the closed hi-hat (a common default setting). If connected to a synth, you should hear staccato note bursts near the low end of the keyboard range.
If nothing is heard, it may be that the MIDI channel needs changing. A set of eight (DIP) switches is recessed below the top edge of the panel, where only a deliberate attack is likely to cause them harm. Four of these are used to set the MIDI transmit channel.
If the sound is there but the feel isn't right, an adjustment of the Pad Sensitivity may be all that is needed. Turning the sensitivity to zero disables the MPD4's MIDI output, which is preferable to turning off power - and losing the current settings. Finally, if all else is right but the sound or pitch is not what you want, go into Sound Set mode, hit the Sound Set switch once, rotate the Value knob while playing the pad until the desired sound is heard, and tap the Sound Set switch once more to return to normal play mode. Tuning occurs in semitone steps over a range roughly from C0 through D6 - well past both ends of the standard five-octave MIDI keyboard. To prevent possible confusion, note events are generated at constant velocity in Sound Set mode.
Since the MPD4 will often be used with a MIDI drum machine or keyboard, a more direct method of programming is included: connect the other instrument's MIDI Out to the MPD4's MIDI In and then play the pads or keys until you hear what you want. Upon exiting Sound Set mode, the MPD4 will remember the last note number it received, and will produce the same note number when played. Easy.
A footswitch input allows "shifting" of the transmitted MIDI note number. Actually, the MPD4 simply remembers two different note numbers, one for each position of the footswitch - for example, low and high toms, or octaves on a synth bass patch. The alternative note number is programmed by holding down the footswitch while following the Sound Set procedure described above.
One of the four DIP switches not associated with the MIDI channel alters the action of the footswitch from "shift" to Hi-hat mode. This feature is quickly becoming common on pad-to-MIDI converters, and is the same as shift mode, except that the "shift" sound is triggered when the footswitch is actuated. Typically, this is used for closed hi-hat sounds.
Two other DIP switches select gate time (note duration) control options for note messages. In the simpler option, the Value knob directly controls gate time over a range of roughly ¼ second to two or three seconds, and may be adjusted while playing. The more sophisticated option provides velocity control over gate time, with harder strikes producing longer gate times.
The remaining DIP switch is used to enable or disable merging of incoming MIDI messages with those generated by the MPD4 itself - useful if other MPD4s are to be daisy-chained.
The MPD4 will accommodate up to three additional pads, Octapad-style, via ¼" inputs. "Normal" and "shift" note numbers are adjustable for each external pad, though gate settings and pad sensitivity are not. (It's no surprise that the Boss BP1 pad looks like a stripped-down version of the MPD4 and is touted in the manual as an ideal accessory for the MPD4, and has a built-in sensitivity control). Hi-hat mode, which works only with the internal pad, defeats "shift" of the external pads, as it should.
In spite of the provision for external pads, however, some quick accounting shows that unless you come up with these pads for free, the price of an MPD4 with three external pads will be more than half the price of an Octapad. On the other hand, the money you save with this setup would cover a few fairly respectable drum machines at the lower end of the price spectrum. Ultimately, the MPD4 works and if it meets your requirements, there's no reason to spend more money.
Prices MPD4, £145; Boss BP1, £41.50 including VAT
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Review by Matt Isaacson
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