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Midi By Example (Part 5)

That syncing feeling


You buy a machine because your drummer can't play in time, then find your machine won't play in sync...

There are many good reasons for programming the rhythm parts of a song on your drum machine. You may prefer playing the rhythm using the onboard pads or maybe it's just down to how easy you find the process of working with a drum machine. It may even be that the machine you're using has real-time playback qualities which cannot be conveyed over MIDI, such as slight timing or tonal variations to give your rhythm tracks a more 'human' feel.

But of course, other parts of your song are likely to be recorded on a sequencer, and irrespective of whether you program the rhythm part first or last, at some point you'll need to get the drum machine and sequencer to play in time with one another. Such a process is usually referred to as synchronisation, and it's usual to have the sequencer controlling the drum machine's playback timing. This means that the sequencer adopts the role of the master and the drum machine becomes the slave.

In the early days of sequencing, synchronisation was achieved by a master device sending out an audio pulse each time it moved from one sequencer step to the next. On receiving this pulse, the slave would do likewise and so keep in 'sync' with its master. In a MIDI system, the pulse is provided by a special MIDI message called a MIDI Clock and for this to be received by the drum machine, the MIDI Out from the sequencer has to be connected to the MIDI In of the drum machine with the sequencer's MIDI Sync Out and the drum machine's MIDI Sync Receive functions being turned on.

Figure 1: Standard set-up for a sequencer controlling the timing of a drum machine


The configuration of this system is shown in Figure 1, and you'll notice that various messages are used to keep the two devices in sync. Have a look at the Glossary for detailed explanations of these.

Figure 2: A complete MIDI system of sequencer, drum machine, synth and sound expander using a MIDI Thru box


So how do you connect a drum machine into your system? Take a look at Figure 2 which includes the common configuration of synth, sequencer, sound expander and drum machine. Here you'll see that the MIDI Out from the synth connects to the MIDI In of the sequencer so that notes and other MIDI performance information can be recorded. The MIDI Out from the sequencer then connects to the MIDI In of a MIDI Thru box so that MIDI information can be distributed to all other units of the system - although you could use a daisy chain arrangement here if you wish (Figure 3).

Figure 3: A similar system but using a daisy chain arrangement of MIDI connections


While the keyboard and sound expander need to get the note and performance information intended for them, the drum machine only needs the MIDI Sync messages. And, while the sound-generating members of the system will ignore these sync messages, the drum machine may well react to the incoming MIDI notes. This was explained in Part 4 of MIDI By Example and to ensure that this doesn't happen, you'll need to check that that the MIDI Note Receive (or similar function) on the drum machine is turned off.

What happens if you want to play a sequencer and multi-track tape recorder in sync? Well, that's another story...

MIDI GLOSSARY

This month some terms relating to MIDI Sync...

MIDI Clock

To keep two sequencers in synchronisation (and remember that a drum machine is effectively a sequencer), a timing pulse has to be sent from one, called the master, to the other which is known as the slave. This pulse is called MIDI Clock and 24 such messages are transmitted from a master in the course of each quarter note. While each MIDI Clock is actually a single number sent from the master to the slave, the idea of a 'pulse' remains - the regularity of the messages is usually referred to as being 24 pulses per quarter note (ppqn).

MIDI Start

There would be little point having two sequencers playing in time if they didn't start together. When the Play button of the sequencer (the master) is pressed, a MIDI Start message is sent to the slave to prepare it for the arrival of the MIDI Clocks which it subsequently sends.

MIDI Stop

In the same way that you need both master and slave to start playing together, it is also usually desirable for the two units to stop simultaneously once you've hit the Stop button on the master unit. Hence, pressing Stop sends out a MIDI Stop message from the master sequencer to the slave so that the two cease playing at the same time.

MIDI Continue

Pressing Stop on the master sequencer causes it and the slave to halt. Hit Play again and the master will play on from where it stopped but the slave starts again from the beginning. That is, unless the master sends out a MIDI Continue message when Start is pressed after Stop - which most do. Pressing Stop twice will usually get the master to start again from the beginning.

Song Position Pointer

Starting a sequencer in the middle of a song will, under normal circumstances, cause a MIDI Start message to be sent out which makes the slave commence from the beginning - a situation which is of little use. To get around it, the master sequencer sends out a Song Position Pointer message which tells the slave precisely which position in the song to locate to. Ensuing MIDI Clocks then keep the two machines in sync.


Series

Read the next part in this series:
MIDI By Example (Part 6)



Previous Article in this issue

Metra Sound Soundcard 1

Next article in this issue

Studio Audio SADiE


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

 

Music Technology - Jan 1993

Topic:

MIDI

Syncronisation


Series:

MIDI By Example

Part 1 | Part 2 | Part 3 | Part 4 | Part 5 (Viewing) | Part 6 | Part 7 | Part 8


Feature by Vic Lennard

Previous article in this issue:

> Metra Sound Soundcard 1

Next article in this issue:

> Studio Audio SADiE


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