• MCS Percussion Computer
  • MCS Percussion Computer

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Drum Machine Supplement

MCS Percussion Computer



Movement computer systems have just brought out an updated version of their versatile percussion computer (which was reviewed in E&MM Jan '82). The original version was based around a Nascom Computer which controlled a range of synthesised and digitally sampled percussion voices. A standard QWERTY type keyboard was used to enter commands and allowed Basic along with wordprocessor software to be used. Voicing controls and trigger switches were provided above the keyboard. Information was output to the user by a separate TV monitor which sat on top of the MCS casing.

The new version has been configured to be a sophisticated studio rhythm unit rather than an add-on for the Nascom II computer, but Basic and Wordprocessor software can still be supported. The casing is moulded in glossy finish fibreglass with a rack mounted section in the top half and control keyboards in the bottom half.

The rack section contains 9 modules consisting of a master clock module to control tempo with sampled hi-hat and cymbal voices, a VDU monitor module and 7 voice modules each having 2 sampled sounds and 2 synthesised sounds.

The lower section has a QWERTY type keyboard along with 16 keys for voice and accent programming, and reset.

On the rear panel, sockets are provided for direct instrument outputs, mix outputs, cassette interfacing, video and VHF signals, trigger inputs and outputs, RS232 link for a printer and PIO for connections to the computer.

Voicing



One of the seven voice boards.

In a program, up to 14 voices can be triggered on any one beat (or step), but each voice card contains 4 voices making 28 sounds available. The voice panels are split into two halves, the top half representing 'metallic' sounds, such as cymbals, while the bottom half represents drum sounds. Both types of sound can be 'real' or synthesised, selected by a switch beneath the volume controls. The knobs above the volume controls have two functions depending on the selection; in the 'real' mode they control pitch, whereas in the synthesised mode they control sustain.

The 'real' sounds are provided using digital sampling techniques where up to 16K bytes of memory, stored in EPROM, are used to hold the whole sound. Pitch changes are made by changing the rate at which data is read from the memory.

'Rotating' Hi-hat and Cymbal samples are also available from the first four metallic 'synthesised' voices. In this case only a short sample of the sound has been recorded in memory but is read out continuously, envelope shaping being carried out by further analogue circuitry. These short samples are stored in two EPROMs on the clock module, to the left of the monitor. Separate controls are provided to alter the pitch of these waveforms. None of the voices are labelled on the modules or the programming keys, presumably so that the user can configure the system as he or she requires. It would have been useful to provide writing space by the modules and keys for user labelling.

The sounds supplied with this machine were as follows:

Top 'Real' — Hi-Hat close, Hi-Hat open, Bell tap, Cymbal, Short Cymbal tap and Cowbell.
Top 'Synth' — The first four use digital 'rotating' samples, shaped with analogue circuitry, allowing pitch and decay to be adjusted. The first two being Hi-Hat and the second two Cymbal. Sounds for the last three modules are: resonant downwards noise sweep, resonant noise with fixed pitch and clave.

Bottom 'Real' — Bass drum, Low, Mid and High Tom-Toms, Snare short and long, and Tambourine.

Bottom 'Synth' — Bass drum, Low, Mid and High Syndrum, Snare with high and low white noise, and a high pitch 'tweak' (to indicate steps when programming).

Operation



When the machine is first switched on, a 'menu' of 5 system options is displayed on the screen. The options are: D for drums, that is, rhythm machine; T for track sheet, which can be used to enter and store studio information such as titles, recording levels, invoicing etc; V for verify tape; E to enter Basic and Y to enter the word processing mode which can be used to write lyrics and output them to Imp or Epsom printer.

Percussion Machine options.

Normally D would be entered which brings up a second menu for command entries: C to continue, H for high resolution start, and N for normal start. Entering normal start displays another menu. For most compositions, the normal start is used, and high resolution simply runs the system faster to accommodate precise rolls, flams and complex paradiddles. The choices are: C to compose, P to play or modify, E to erase, T to transfer, R to run assembly, A to assemble rhythms, I for Information Sheet and S to save on tape. One of 10 possible page numbers is entered (0-9) and the selection made.

Composing page.

Compose — The rhythm number (0-9), allowing 10 rhythms per page, can now be entered along with a name for the composition. Once the beats per bar (really total pulse or step count) and number of bars have been entered, the machine's metronome will start using channel 7 sounds — the upper voice triggered on the down beat and the lower voice triggered on each main step. The tempo is now displayed on the screen, ranging between 0 and 99, and can be adjusted with a control on the master clock module. A fine control tempo switch is also provided. Voices are added by pressing the appropriate voice trigger buttons on the required beat. To erase, pressing selection key E followed by the appropriate voice trigger button on the beat will erase the sound. To program multiple beats, R (repeat) can be pressed and a voice key held down so that the voice will now be triggered on subsequent steps.

The space bar stops the rhythm and displays the compose options. These are: 0 for off-beat; S for shuffle; D to clear all lower row voices (drums); C to clear all upper row voices (cymbals); I to insert metronome; K to kill metronome and M to multiply bars. When a selection has been made the display returns to 'running'.

Rolls and flams can be entered by setting the off-beats to x2, or x4; beats can now be entered, between the main steps.

Play — Will play through the selected page.

Erase — Complete pages can be erased but with a check entry to make sure you think twice before erasure.

Transfer — One page can be transferred to another with a new name allocated if necessary.

Run Assembly — Will play an Assembly of pages. Pressing Res-Go key will pause the selection or display page assembly prior to running, continuing on alternating depressions.

Assemble Rhythms — Sequences of pages can be strung together using Assemble.

Information Sheet — Used to retain your own typed in notes about the program you're creating.

Save on Tape — The total pages used must be specified, 0-9, which is then dumped on tape when T is pressed. A Load is automatically operated when the unit is switched on from an external mono cassette recorder.

Circuitry



The computer used as the basis of the system is a NASCOM II with a Z80 microprocessor. Up to 48K of dynamic RAM can be supported for programmes, with 32K supplied as standard. The Track Sheet and Wordprocessor firmware are available as options costing £27 each.

Internal construction of the MCS II.

Internal construction is neat as can be seen from the photograph. The voice cards (far left) plug into computer grade Eurosockets, wire-wrapped together. Situated next to the voice boards are the VDU driver and the clock/rotated-voice card.

Beneath the VDU is the NASCOM II board and the 48K dynamic memory card. The power supply board is mounted on the rear panel, which acts as a heatsink for the 5V regulator. Two transformers are used, one for logic supplies and the other for the voicing.

All of the voice cards are similar, with space for up to 16K (4 x 4K) of EPROM for both 'real' sounds (see photo) and plug in boards to configure the analogue sounds.

Conclusions



MCS have now provided the hardware to make their percussion computer into a more viable music-making machine. When you purchase the MCS, you can have your own drum samples installed free. Your own choice of 'real' voicing can be digitised, at £22 a sound at a later stage and plugged into the voice cards, although development is underway for a plug-in 16K CMOS RAM card, with battery back-up, which would allow any sound to be sampled by the user and triggered when required.

Another interesting development, which is on the designers' drawing boards, is the ability to program the sounds from drum pads, which will also allow dynamics to be stored.

The exciting thing about computer-based systems is that software can always be updated. MCS have provided some great sounds together with versatile open-ended hardware which ensures that the machine will not be obsolete in years to come.

At £2,300 inc VAT, the MCS II is an interesting contribution to the growing field of computer musical instruments.

For more details contact Movement Audio, (Contact Details).



Previous Article in this issue

Klone Kit

Next article in this issue

Korg KPR-77


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

 

Electronics & Music Maker - Feb 1983

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Drum Machine Supplement

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> Klone Kit

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> Korg KPR-77


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