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Music Percussion Computer

More and more manufacturers these days are producing drum machines that rely on digitally sampled drum sounds, so it's quite refreshing to see a new machine entering the market that combines both analogue and digital technology well to produce a hybrid device.

Designed by Clive Button, who was also responsible for the successful Kit, the MPC is the first commercial percussion device to interface directly with a home computer — in this case the Sinclair ZX81.

The MPC can be played in one of three ways: as a 'live' stand alone instrument in its own right, as a drum machine using the onboard processor or linked to the ZX81 for step or real-time programming of rhythms.

To exploit the full potential of the MPC you will need to purchase a ZX81 (if you haven't already got one!) TV monitor and mono cassette recorder of some sort. When you actually buy the MPC what you get is the main unit and the Interface package with ribbon cable and 25-way 'D' socket for connection to the computer. However, this aspect shall be explored in greater depth later but first well concern ourselves with the main unit itself.

Main unit

The MPC measures 540 x 340 x 168 mm and weighs 25lbs. It is built into a robust, silver flightcase with detachable lid and the whole unit can be easily mounted on a microphone stand if required.

With the lid removed the top panel is exposed. This is neatly laid out with eight small, octagonal shaped drum pads arranged in two rows of four that are slightly raised above the beige coloured surface for ease of playing.

To the right of these are located all control knobs pertaining to the 9 individual drum voices available, and a 16 button keypad for inputting record and playback instructions to the internal computer, based on the Z80 microprocessor chip.

Looking at the top panel there are four tom-toms, each with (from right to left) 5 separate controls for Level; Decay, the length of note; Pitch, for tuning the drum; a Mix control which varies the mixture of noise and drum tone and a Bend control which increases the amount of pitch bend that occurs on initial striking of the pad. As well as these, there are two master controls which alter the Pitch and Decay characteristics of the tom-tom skin resonance effect helping add realism to the analogue drum voices. The range of sounds possible from the combined use of these features is quite impressive, giving you authentic sounding toms and even Simmons kit sounds when the Bend and Noise controls are well advanced.

Apart from the lowest two toms (3 and 4), their pitch ranges don't overlap, so it's quite easy to obtain four distinct tom sounds tuned high to low.

The drum sounds are actually activated in the stand-alone mode by striking the pads with drum sticks (fitted with rubber tips to cut down extraneous noise) which have Piezo crystal contact mics fitted below them. The top row of pads are multifunction; depending upon the status of the Pad Select pushbutton you can have either toms 1 to 4, or toms 3 and 4, cymbal and clap and two LEDs indicate which state you are in. The bottom row of pads always give snare, bass drum, closed and open hi-hats from left to right.

Moving further down the right hand panel controls we have a clap Level which determines the relative volume of the clap sound in the output mix. The handclap sound produced has been deliberately kept short with little decay because handclaps played together on automatic repeat would tend to merge and become indistinct otherwise. The clap sound is completely 'dry' and suffers slightly from this. However, reverb can be added to the voice externally if required using the individual voice output socket on the right side of the unit.

The hi-hat shares the same controls as the cymbal, these being Decay; Pitch, which can be adjusted to resemble different sized cymbals and tone which helps produce crash and ride-type cymbals. Cymbal and hi-hat both have individual Level controls whilst a further control labelled Tight'n, simulates the action of pressing your foot down on the hi-hat pedal: anticlockwise setting of this control gives you a fully closed hi hat sound and vice versa. Although open and closed hi-hat share the same basic voice circuitry, they do have separate pads and the circuitry has been specially designed so that the open hi-hat sound is cut off immediately upon striking the closed hi-hat pad, thus simulating the action of a real hi-hat; a nice touch.

Next we have the bass drum and snare each with Level, Decay and Pitch controls. Bass drum Decay ranges nicely from a short thud to a longer thump whilst Pitch keeps the sound within the encompass of a bass drum yet permitting a slight amount of tuning variation to suit the style of playing.

Snare drum Pitch allows you to tune the snare down to the lower pitch range favoured by most rock drummers (a la John Bonham) and Decay can be altered to increase the drum 'ring'. The final snare control is Noise level which helps simulate the rattle of a real snare drum and works very effectively.

One point to mention is that the ranges of all controls have been fixed so that you can always obtain a reasonable drum sound, no matter where controls are set; a sensible idea.


All of these drum voices are then panned across a fixed stereo image to imitate the conventional line up of a kit and are available at the stereo jack Mix Output socket on the right hand side panel. (The tip and ring must be wired together when inserting a mono jack plug). This is obviously very useful for home recordists as it means you can take the Mix Output to a couple of tracks on your tape recorder and achieve an instant stereo drum balance using individual Level controls to give the desired instrument mix.

However, for those who like to experiment, individual jack outputs are provided for the 9 voices down the right edge panel so you can add effects to each voice or route them to an external mixer. The sounds are actually better quality from these separate outputs as the entire panning/mixing circuitry is bypassed, but you need to turn down the voice Level control when using an individual output as the sound is not removed from the master Mix which also has its own Level control.

Monitoring is provided for 5-800 ohm stereo headphones and the socket for these is conveniently located at the front edge of the right side panel. A very useful feature is the Mute pushbutton alongside the headphone Level control, which when depressed cuts the signal going to the main output allowing headphone monitoring whilst you set up your sounds. A red LED above this button indicates when the main output is active, so you know exactly what state the machine is in.

Asa 'live' percussion instrument that concludes the run-down of sounds available to the player. The instrument really comes alive when these sounds are incorporated with the record and playback facilities of the internal computer.

The complete MPC/ZX81 system.

Internal computer

This allows the user to programme rhythms into the MPC and have them played back and you record these rhythms by playing the voice pads in real time. Non-drummers should not be put off as this is not as difficult as it may first appear to be. The MPC is a very 'friendly' machine that is very easy to operate and quickly mastered.

Rhythms are recorded using a combination of drum pads and the 16 button numbered keypad on the top panel which acts somewhat like the function controls of a tape recorder, having Record, Pause, Play and Stop buttons.

There are four group memories (buttons 1-4) in which to store your rhythms. Initially each of these groups contain a two bar measure with 16 beats per bar that is designed to cycle around continuously.

Having first selected the top row pad functions ie. all tom-toms or two toms, cymbal and clap, you enter record mode by pressing Rec. A metronome output on closed hi-hat is then clearly audible to help with timekeeping whose tempo can be altered to suit using the two keys labelled (5) Fast and (6) Slow. Keeping your finger pressed down on one of these causes the tempo to decrease or increase gradually. This metronome initially sounds on every first beat of four beats (giving you 4 to a bar).

Four LEDs above the group keys will begin to flash together on entering record mode waiting for a group to be selected in which to record your rhythms. You can record in any group in any order you like simply by pressing a group key. The computer will change over to the new group at the end of the two bar measure.

You actually start playing on the first beat of the two bar measure indicated by the four LEDs being on simultaneously then play the pads one at a time or in combination and the rhythms are stored and played back to you immediately. If you make a mistake you can press the (7) Clear key which completely erases the contents of the group you are working on. When satisfied with your rhythms you merely press Stop, taking you out of record mode.

To playback your creations you press Play followed by whichever group you wish to hear. At any point in the proceedings you can re-enter record mode and modify your rhythms. A very useful feature is the Pause key which momentarily stops playback when pressed. Re-pressing it continues the rhythm from the point where you interrupted. This function is duplicated on a foot-switch that connects to the rear panel Run/Stop socket which is an additional accessory.

When in record mode you actually have 7 sounds available from the pads and the top row have various functions in this mode. The fourth pad in record mode is used to programme an Accent in which case the third pad is used to enter both cymbal and clap beats. On playback, a pushbutton below the keypad can be used to select which sound is heard — either cymbal or clap; you cannot have both sounding simultaneously. Obviously this is a limiting factor but planning out your rhythms in advance should enable you to programme all beats for clap/cymbal then manually select the voice for each bar as the rhythm plays.

Toms 1 and 2 cannot be recorded, they are only available for live playing but this turns out to be a plus feature because they can be played on top of your recorded rhythms.

Like the Roland TR808, the accent on the MPC affects all voices occurring on the accented beats. However, unlike the TR808 this accent is done internally on each separate instrument, accent actually increasing the trigger voltage level on each voice and resulting in whole character/tone transformations — it's not simply a VCA increasing the overall volume. Unfortunately, accent is also fixed internally for each instrument and can only be changed by tweaking the presets.


The objective behind the MPC's voices, Clive Button, the designer stated, was to produce drum sounds that were comparable with the sounds of recorded drums (not live drums). Working on the principle that what most users want would be something you could record straight onto tape which would sound like well recorded studio drums. The end result comes pretty close to achieving this.

Once the rhythms have been recorded they can be chained together to form one sequence by pressing Seq, Rec and the required combination of group keys. If you want group 1 to play four times you press key 1 four times. Up to 199 changes between groups is possible and with four groups, this is sufficient for most rock-type songs, but without the ZX81 interface you are limited to one sequence.

Whenever you enter a group as part of the sequence, the relevant LED lights up to indicate a successful recording, which is vital especially when producing a long sequence if you are to avoid mistakes.

Bar length

Up until now all bars have contained 16 beats only, limiting you to 4/4 time. With the internal computer there are four combinations available of bar lengths which are programmed by pressing key B in record mode then one of the four group keys: 1 = two bars of 16, 2 = two bars of 12, 3 = three bars of 12, 4 = three bars of 16. The difficulty here is that the metronome still sounds on the first of every four beats so this must be changed to the first of every three if you require 3/4 time for example. This is achieved by pressing key 'M' followed by a group key. In this mode groups 1-4 give you the first of every 4, 3, 6 and 8 beats respectively, and by combining these metronome beats with the different bar lengths a broad variation of time signatures is possible. Note that pressing Clear resets the bar length to 16 beats which saves having to remember what bar length was already programmed in — a helpful point.

Since the MPC has internal CMOS memory with battery back-up, metronome beat, bar length and sequence tempo are all stored when power is turned off, as is other rhythm information.

Rear panel

Along with the already mentioned Run/Stop footswitch jack sockets are provided for a tape sync facility which allows the MPC to generate or play along with an existing click track using the To Tape and From Tape connections.

A 25 way 'D' socket allows connections to the external ZX81 computer. Two 5-pin DIN sockets labelled Sync Out and Sync In are capable of interfacing with most sequencers, drum machines and synths. You can use this facility to run one such device into the MPC to drive it, then use the MPC to control another unit whilst being able to control the whole system from a tape click track — an especially useful feature for film music and jingle composers.

A 25-way 'D' plug has also been provided to enable larger external stage pads to trigger the MPC. These are a planned addition not yet available which will give access to all drum sounds simultaneously, whereas currently there are only 8 pads and some sharing is undertaken. Also a cymbal stop feature will be accessible which is like hitting a cymbal then damping it by hand.

The final two jack sockets enable a pad change, over footswitch (duplicating the front panel pushbutton function) and a bass drum pedal to be connected. The bass pedal has a valuable function since it lets you play bass drum from the foot pedal rather than the pad, which feels more natural to conventional drummers and has the added bonus of freeing one of your hands to play a third drum if necessary.

ZX81 interface

MPC Interface unit.

The MPC's sequencing facilities are greatly expanded when the unit is linked to the Sinclair ZX81 computer. An Interface is provided with the MPC complete with ribbon cable and 25-way 'D' plug for connection to the main unit. This is a RAM-type black plastic case with an edge connector which clips onto the back of the ZX81. The Interface unit retains the system program itself which contains facilities for composing up to 26 rhythm bars, 9 sequences of these bars with as many repeats as necessary, and the capability of arranging the sequences into a maximum of 9 'songs.'

With the additional 16k RAM pack memory expansion, the number of sequences and songs increases to a maximum of 25 each, and a song can be between 1 and 64 sequences long.

The ZX81 is only really servicing the TV screen but for the extra cost of building in an equivalent computer it's actually cheaper for people to buy their own computer (currently selling at £39.95 at W. H. Smith's).

Having connected the Interface, ZX81 and MPC together the rhythm program can be run. On typing in an initial command a Master Directory appears on screen as follows:

1 Compose Bars
2 Make Sequences
3 Compose Songs
4 Save Songs
5 Load Songs
6 Download

Selecting 1 for example causes a display of two empty bars to appear on screen, with a line of 16 divisions for each voice: hi-hat open, hi-hat closed, hi-tom, lo-tom, snare, bass and cymbal. A tempo readout is given in beats per minute on the top right of the screen. Below these bars are a list of available instructions that can be performed by the user. Rhythms are actually written initially in step mode by moving a cursor about the screen, controlled from the four arrow keys on the ZX81 keyboard, and plotting your beats on the rhythm matrix by pressing the letter 'Q'. An asterisk symbol then appears wherever a beat has been written. To erase a beat, simply move the cursor to the required beat and press 'W'. To play the finished bar you have written you type in '?', which is the instruction for 'Test Play Bar'; the bar then plays once through.

Accents can be programmed in by typing the letter 'A' above the required beat, which is then displayed or press 'A' again to remove the accent. At any point in the programming you can return to the Master Directory by pressing 'Newline (Enter)' on the keyboard.

All of the functions available on the internal processor when composing bars are also available with the ZX81 connected, such as metronome beat, tempo modification, clear bar memory as well as some useful extra facilities.

Copy bar (K) for example, allows previously written bars to be copied into new sections of memory saving unnecessary work. Since only two bars can be displayed on screen simultaneously, the select bar (S) feature lets you decide which ones. Also, using functions 'C' and 'E' permits any individual bar to be contracted or expanded in the number of beats ranging from 1 to 20. In this way, 20 beats per bar would enable a 5/4 time rhythm to be composed for example. It also lets you write in unusual time signatures or short drum fills.

Instead of entering beats with the cursor, you can choose to use the drum pads to trigger the sound, but you still need to step the cursor onto the next beat manually. However, if Hand Entry (H) is selected a metronome output is heard as the bar you wish to compose cycles around. The drum rhythm can then be entered using the pads, with the drum used and beat both being plotted on the screen as you play! To stop composing you simply press 'Break' on the computer.

Having entered a rhythm in either step or real-time mode you can go back and edit the bars, again either in step or real-time; a very handy feature indeed especially if you can 'feel' a rhythm but not know exactly which beats you need to programme to achieve it.


Once several bars have been composed they can be organised into sequences by selecting 'Make Sequences' from the Master Directory, causing a display of two lots of 8 dots in 4 columns to appear. These dots represent the empty bars (a maximum of 64) and you write a sequence by pressing combinations of bar letters as many times as necessary, and the bar names appear on screen. Only nine repeats of a bar or group of bars is possible but repeats can be nested to produce an infinite number.

Songs can be compiled from either bars, sequences or a combination of the two. If you require time changes within a song then you must use sequence chains rather than bars since bar tempos are not remembered individually. This is an intentional feature so that bars can be interchanged easily between different sequences without recourse to modifying each bar tempo separately.

All song data can be dumped onto a standard mono cassette then re-loaded at a later date. Since the Interface memory is volatile this is a necessary requirement. As well as this the complete 25 songs can be downloaded to the MPC's internal memory, but songs then can only be played back from the unit, not modified, as the limited keypad makes individual parameters inaccessible. Thus all editing of rhythms must be done in advance. One point to mention is that the actual drum sounds can be modified during any part of the record/playback operation, as can the overall tempo of the songs. A bonus feature is that with downloaded songs you can overdub toms 'live' as the pads remain active.

A cassette tape is soon to become available with 25 pre-programmed rhythms on one side and 9 the other, enabling it to be used with the expanded or unexpanded Interface versions. By loading the rhythms into the Interface, two-bar measures can be displayed to give users an idea of what can be achieved by the MPC.


Designer Clive Button with the MPC.

The MPC is an extremely well-crafted, cleverly designed unit that makes good use of the home computer link-up. Internal construction is to a very high standard, having three neatly soldered PCBs and compact cabling.

The main unit is clearly laid out, straightforward and easy to use. The onboard processor functions are very quickly mastered, as are those of the ZX81. The ability to play and then analyse a rhythm is particularly useful to non-drummers. No previous computing knowledge is necessary to operate the system successfully and the overall package can only be described as extremely 'friendly'.

The pad and hi-hat voice sharing may present minor problems and the capabilities of the onboard computer are not really extensive enough, especially being limited to only four memory groups in which to record rhythms and one sequence.

Ordinarily these would only be small criticisms, but placed in the context of the asking price of this system they become major. Remember you still require a ZX81, TV and cassette recorder if you don't already have them and this puts the package well into the price range of digital drum machines such as the Oberheim DX or Drumulator whose sounds are in a different class altogether.

Having said that it is the overall system that is most appealing. The analogue voices are certainly some of the best around and the big advantage is the fact you can actually physically 'play' the machine like a normal kit. As everybody else turns digital, Clive Button has taken a brave step in another direction with the MPC — only time will tell if he has taken the right one.

The recommended retail price of the MPC is £875.00 including VAT. For further details contact Atlantex Ltd, (Contact Details).

Also featuring gear in this article

Previous Article in this issue

Atlantex/MXR 'Kit' Competition

Next article in this issue

Advanced Music Synthesis

Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.


Electronics & Music Maker - Aug 1983

Review by Ian Gilby

Previous article in this issue:

> Atlantex/MXR 'Kit' Competiti...

Next article in this issue:

> Advanced Music Synthesis

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