MIDI and drum machines have gone hand in hand for a number of years, but so far only one model - Sequential's Tom - has been given an implementation of MIDI Mode 4. It should encourage others to do the same.

FOR MANY MUSICIANS, MIDI and drum machines still don't quite go together. Sure, people use MIDI-equipped beat boxes, but because little has been specifically laid down for drum machines in the MIDI spec, too many of those users don't make the most out of MIDI on a drum machine the way they would on a synth or a sampler, say.

But think about it for a minute. The MIDI Clock has worked wonders in the area of synchronisation, replacing the vast range of sync standards and other incompatible systems which existed before MIDI.

And the Start, Stop and Continue commands, in conjunction with the MIDI Song Pointers, go further than ever before to the development of a drum machine/sequencer system which can be rewound or fast-forwarded and then started at any point in the song, with all the separate machines still knowing exactly where they are supposed to be playing from. Adding a suitable SMPTE-to-MIDI converter means this process can be controlled from a multitrack tape machine, allowing valuable tape tracks to be freed for things that can't be sequenced: vocals, guitars, and the rest.

But all these worthwhile practices are based on the assumption that you're recording and playing back your drum patterns on the machine itself. What about programming drum parts from a keyboard or pads - so often a more "musical" way of entering drum parts? Or triggering the sounds from a MIDI sequencer?

Well, most MIDI drum machines do allow you to do this, but there is no standard format laid down for the way in which it's done. Different manufacturers have evolved various systems using MIDI note number assignments. So, if you record a drum part onto a sequencer using one machine and then decide to play it back on another, you'll get a highly unpredictable (and probably unusable) result.

The first MIDI drum machine on the market, Sequential's Drumtraks, assigned its various drum sounds to notes in the bottom couple of octaves of a standard five-octave keyboard. This same system of allocation was carried over to the Tom, which assigns its drum sounds to exactly the same keys when in MIDI Modes 1 and 3. Roland's TR909 used a similar system, but (unfortunately) not the same allocation. Still, the two manufacturers' systems are sufficiently similar for users to be able to trigger one from the other without too many problems, so all three of these drum machines can be played from the first Roland Octapad preset quite easily.

When Yamaha entered the MIDI drum machine market, their RX11 and RX15 allowed the user to assign a MIDI note number to each drum sound, and this assignment was remembered even when the machine was switched off.

More recent Roland machines like the TR707, TR727 and TR505 (and also the Octapads - designed for playing the sounds in drum machines via MIDI and thus recording rhythm patterns into MIDI sequencers) give the best of both worlds, with preset assignments which come close to being standards, coupled with the opportunity to change individual note assignments if incompatibilities occur.

Now, on drum machines that allow dynamic tuning of sounds (ie. where the pitch of a sound can be continuously changed between one hit and the next and then memorised within a pattern) some way had to be found to make this facility available via MIDI.

E-mu Systems added a special function to their SP12 to treat incoming MIDI note numbers as tuning controls instead of triggers for different drum sounds.

When originally released, the Drumtraks had dynamic tuning but no way of accessing it through MIDI. A software update (version 0.5, which should still be available though your nearest Sequential dealer) changed this and made tuning available via MIDI in two ways: first by using the bend wheel on a synth to change the pitch of the last sound triggered, and second by holding down the note which triggers the sound you want, and then choosing from a 16-note range just above Middle C which acts as the tuning control.

The new Korg DDD1 uses the same area of the keyboard to achieve tuning control (and the area below the MIDI note triggers for decay controls).

The problem with this method is that you can only control one sound at a time via MIDI. Now, this isn't so bad if you're using the internal patterns of the drum machine to sequence your drum sounds, and are only using the MIDI controller (keyboard or drum pads) to play the patterns in one part at a time, as the drum machine only needs to be able to recognise one tuning instruction at a time. (The others, if there are any, are already stored in the machine's internal patterns which don't use MIDI assignments.)

But if you send the data to be recorded on a MIDI sequencer (via the Thru socket on your drum machine) and then try to "overdub" another drum part which uses tuning control as well, you'll have trouble when replaying your drum part. Why? Because there's no way for the drum machine to know which sounds the tuning amounts are meant to refer to, and some strange tunings are likely to result.

The answer Sequential found to this problem on the Tom was to use our old friend Mono Mode. By putting each drum sound on a different MIDI channel, you can use all the MIDI note numbers to represent different pitches.

Well, that's exaggerating a little. Internally, the Tom allows for 32 different tunings of each drum sound. In MIDI Modes 1 and 3 (Poly Mode with Omni On and Off, respectively), the tuning ranges lie above Middle C (so as not to interfere with the MIDI note numbers used to trigger sounds) and are restricted by the lack of space on four- and five-octave keyboards.

But in Mode 4, where the sounds are selected by the MIDI channel the data arrives on, the note numbers for determining pitch start at the bottom end of a five-octave keyboard. This means that C1 (MIDI note number 36) causes the lowest pitch of the selected instrument to sound. This makes F#3 (66 in MIDI terms) the highest pitch of the 32-note range.

So now you can use this note range to control all 15 available sounds independently over the Tom's full range on separate MIDI channels.

The channels which the Tom assigns each drum sound to are as follows:


Bass Drum 1
Snare Drum 2
Tom 1 3
Tom 2 4
Open Hi-hat 5
Closed Hi-hat 6
Crash Cymbal 7
Claps 8
Cartridge 1 9
Cartridge 2 10
Cartridge 3 11
Cartridge 4 12
Cartridge 5 13
Cartridge 6 14
Cartridge 7 15
Trigger Out 16

Clearly, if you're simply playing patterns which have been pre-recorded on the Tom into a MIDI sequencer and then replaying them on the Tom from the sequencer (see Diagram 1), you don't need to know this allocation.

All you have to do is put the Tom into Mono Mode before you start recording, make sure it's in Mono Mode before playback, and everything should come back exactly as recorded, no matter how many of the Tom's instruments you are using with tuning variations.

Don't forget you can also send and receive the "special" key note numbers the Tom also implements in Mono Mode. These are C#4 (note 61) for instrument direction, which governs whether the sound is played forwards or backwards, and D4, D#4 and E4 (62, 63 and 64) which set the stereo panning of the sound to left, centre or right respectively.

The Tom's Mono Mode implementation also allows for additional data which can't be transmitted or received at all in the other modes. Notes F4 (65), G4 (67), A4 69) and B4 (71) all control the amount of "flange" an instrument sounds with, provided the Stack control on the Tom is switched on. This effect is achieved by detuning the sound against itself; B4 gives you the maximum flange effect, while F4 turns the effect off completely.

Overall, the Tom's implementation of Mono Mode has a good many more uses than the simple transfer of drum patterns to a MIDI sequencer intact. You can use the transmission on multiple channels (another example of the implementation of Mono Mode beyond that provided for in the MIDI spec) to trigger a sampler which is also in Mono Mode. In fact, if you use the assignment I suggested in our Mono Mode feature on the Prophet 2000, you'll find the bass drum, snare drum and toms trigger as they are.

But one aspect of the Tom's Mono Mode that may cause you a few headaches is the fact that each MIDI channel is assigned its own sound, meaning that drum sounds may trigger on channels that are meant to be sequencing other things (keyboard parts, for example).

You can reduce this problem by taking the cartridge out of the Tom and not using the trigger output. This will allow channels 9-16 to be used for other MIDI devices; nothing will sound from the Tom as the sounds which would normally be triggered on the machine are just not present.

If it's possible to assign different MIDI channels to each pad on your MIDI drum controller or electronic kit, you'll be able to play the sounds on the Tom in Mode 4 and record them onto a MIDI sequencer simultaneously. This is most easily achieved on a sequencer which can "Mix" MIDI Out and Thru signals, as Sequential neglected to put a MIDI Thru socket on the Tom. Using such a system, you'd connect your pads, sequencer and Tom as shown in Diagram 2.

If your sequencer doesn't have a Mix facility, you'll need to use a MIDI Thru Box, and you'll have to keep replugging the MIDI cables as shown in Diagrams 3a (for recording drum parts) and 3b (for playing them back).

The Tom's ability to receive in Mono Mode is mirrored by a similar ability to transmit on more than one MIDI channel (an ability not strictly within the confines of Mono Mode which, according to the 1.0 spec, enables a machine to receive on multiple channels while still transmitting only on the base channel). This means you can send to other machines which receive in Mono Mode, like the Prophet 2000/2 and Akai S900 samplers. By sampling drum sounds on the same MIDI channels as Tom's assignment, you can trigger these direct from the patterns on the Tom.

We can see, then, that there are myriad ways of using Mono Mode on a drum machine. Unfortunately, no other manufacturers have noticed this yet, so our investigation of Mode 4 in this area must end as abruptly as it began.

Next time, we'll move on to see how Mono Mode makes itself indispensible to the MIDI-equipped guitarist.