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CM Automation

Article from Music Technology, November 1992

New fast automatic knob twiddling

Why it's taken so long for MIDI control to be incorporated into mixing desks remains a mystery. But now it's here, choices have to be made: do you risk losing your shirt selling your existing mixer second-hand or do you bring it up to date with a little add-on automation...?

Whilst it's great to see companies like Allen & Heath and Soundcraft now starting to incorporate VCAs (Voltage Controlled Amplifiers) into their recent budget mixer designs, it is of little comfort to those who could benefit from this kind of MIDI control, but who are saddled with conventional desks. There are, however, a couple of ways of overcoming the problem. The first is a VCA retrofit which, though generally giving excellent results, will probably cost more than the mixing desk itself (and it is doubtful whether the noise threshold of most desks is low enough to justify such a retrofit).

The cheaper method is to use an external unit which connects to the mixer either through the line inputs or the insert points. One such unit - the MX-816 - has just been developed by CM Automation in the USA and brought over to this country by AMG - better known, perhaps, for their sample discs and sound cards.

As you might imagine from its rather utilitarian nature, the MX-816 is a fairly uninspiring piece of kit to look at: a standard, grey coloured, 1U rackmount - with few visual indicators as to its precise function. It is available in two versions - 8 and 16 channel - with the option of upgrading the 8 channel version to 16 through the simple addition of a circuit board.

Connection hardware includes phono In and Out sockets mounted in pairs on a plastic block with a single screw holding it to the rear panel. I say 'holding', but in fact, pushing phono plugs a little too hard can lead to the sockets disappearing through the rear panel! Perhaps the review model had been (mis)handled by various other people before I got hold of it, but relying on plastic screw threads to withstand the pressure imposed on phono sockets when inserting plugs seems a mite optimistic to me. Having said that, I suppose you could argue that once in place, the unit is unlikely to be connected and reconnected very often, so this problem shouldn't arise.

Power is via an external unit - presumably to keep noise and hum levels to a minimum - the only other sockets being Sum Out and the mandatory MIDI In and Out. I was a little concerned to read in the manual that pins 1 and 3 of the MIDI In socket are used to provide 9VDC phantom powering for "future expansion". Such a system is likely to be proprietary and certainly not part of the MIDI Specification. Consequently, great care must be taken to ensure that only correctly wired MIDI leads are used with the MX-816.

As for the front panel, this is a very sparse affair with just four function buttons and their associated LEDs to show you when each of these are active.

The MX-816 is essentially a 'dumb' unit: it has to be sent MIDI Controller messages to operate the VCAs. These can be provided from a hardware unit such as the JL Cooper FaderMaster or from the relevant page on many sequencers which allows you to output MIDI information from the movement of on-screen faders. Either way, the MX-816 requires you to set up a number of faders (8 or 16) each with a different MIDI Controller number - the only proviso being that they must be consecutive.

To some MIDI users, this may prove a little difficult to get used to. Most MIDI Controllers have specifically defined applications. For instance, MIDI Controller #1 is defined as Modulation and MIDI Controller #7 is Volume. Where the MX-816 is concerned, however, it ain't necessarily so. But while the system used by CM Automation does appear to ignore the precedents established for MIDI Controllers, it has the advantage of letting you use low numbered Controllers which many sequencers are able to 'chase'. Consequently, you can start a sequencer in the middle of a song and have it send out the correct automation settings immediately.

Hitting the first button, 'Fade', and moving the fader for the first audio channel is all that is required for the MX-816 to set up all other channels for consecutive MIDI Controllers. Once done, you have your basic MIDI automation system up and running and ready to do your bidding.

There are many occasions during recording and mixdown when you need to set up channel volumes and recall them instantly. To this end, the MX-816 has 100 Snapshot Scenes which will capture all current levels and can be recalled via the relevant MIDI Program Change number. Additionally, you can determine the fade time taken for current levels to change to the levels for a recalled patch. CM Automation have developed a rather clever system for this: once you have the levels as you want them, you press the second button to enter 'Patch' mode, and then hit any key on a keyboard as many times as you want the fade up time to last in seconds - to a maximum of 30.

Both the levels for a Snapshot and the fade time can be adjusted for an existing patch simply by entering Patch mode again. You can also clear the current memory, and return all faders to an open position by pressing and holding the 'Max' button for two seconds.

But while moving between snapshots and using the fade function may be fine for 'scene changes', what happens if you want to fade all channels in or out? What if, for instance, you require a 20 second fade out at the end of a song? Well, the MX-816 has 28 pre-programmed fades which act on all audio channels simultaneously and are accessed via MIDI Program Change numbers 101 to 128. Even-numbered Program Changes handle fade ins while odd-numbers deal with fade outs.

Thus, Program Change #101 provides a two second fade out, Program Change #102, a two second fade in - and so on, in two second steps up to the maximum of thirty seconds.

What makes this a little awkward is the fact that a fade time is based on the full travel of a fader. In practical terms this means that the audio on some channels will disappear sooner than others, dependent on the current fader position - although the high attenuation range of 98dB means that the effect of this is not all that apparent.

One particularly innovative idea is that of panning snapshots. By using the MIDI Controller directly above that for the highest numbered fader, a 'Joystick Fader' can be defined. When this Controller is set to its highest value (127), all levels are taken from the current scene; when the Controller has a value of 0, all levels are derived from the previous scene. Any value in between will set a balance between the levels for the two scenes.

Of course, the MX-816 can also be used as a straightforward MIDI muting device, and given the innate noise levels of some sound modules, this is likely to prove extremely useful in many recording setups.

Muting is carried out through the use of MIDI Notes On and Off. The final button on the front panel, 'Mute', allows you to set up one of three possible modes: Toggle Mode ignores Notes Off - a MIDI Note On mutes and a subsequent MIDI Note On unmutes; Gate Off Mode uses the Note On to mute and the Note Off to unmute; Gate On Mode has this the other way round and uses Note Ons to mute and Note Offs to unmute. The point of the last method is to allow you to effectively 'play' a device which you are trying to quieten. For instance, a noisy synth can be permanently muted and only unmuted when you hit, and hold, the note on the keyboard.

All three modes require you to set a Base Note for Audio Channel 1, after which all audio channels are numbered consecutively. The note above the highest one required is used for globally muting the entire unit.

All edits are saved to an internal EEPROM (Electrically Erasable Programmable Read Only Memory) chip which should hold data for ten years or more. However, all data (Fader and Mute Set-up Tables, Snapshot Scenes) can also be output to a librarian device either as a bulk dump or per snapshot (in the case of the snapshot scenes). Similarly, the current status for individual faders can be requested and this opens up the possibility of dedicated computer editors/controllers being written for the MX-816.

The MX-816 is not expensive for what it offers. The facilities included - and their implementation - are well thought out and easy to use in practical terms. If you have a particularly quiet mixing desk you will probably notice a slight increase in hiss level once the MX-816 is connected into the system, but if you are using a number of synths or sound modules, the level of noise is likely to be less than you usually have to put up with anyway!


Prices: 8 channel; £345, 16 channel; £579, 8 channel expander; £235

More from distributor: AMG (Contact Details)

As I pointed out earlier, for those with otherwise adequate mixing desks who watch with consternation the development of ever-cheaper MIDI-controlled designs, the range of options is not great and the MX-816 could well be the answer to their dilemma. Certainly, for anyone working to a budget, the ability to semi-automate an 8 or 16 channel desk for less, respectively, than the price of a typical expander or synth is not to be sniffed at.

Getting It Into Your System

The simplest way to connect the MX-816 is to route the outputs from your synths, multi-track recorder, effects units and so on, into the inputs of the unit, and route its outputs to the inputs of your desk. As any noise generated by the unit will be amplified by the desk input circuitry, this method may produce slightly higher noise levels than would occur using your mixer's insert points as a means of connection. But in practice this was found to be negligible.

The Spec

Signal to Noise: better than 95 dB
Total Harmonic Distortion: less than 0.01% (non-weighted)
Input/Output levels: -10 or +4 dB (over +22 dB maximum)
Frequency Response: 10 Hz - 30 kHz (+/-1 dB)
Attenuation: better than 98 dB at 1 kHz
Dynamic Range: better than 106 dB
Noise level: better than -95 dB
Input impedance: 20 kohm
Output impedance: 150 ohm
VCA chips: dbx 2150A

Also featuring gear in this article

Previous Article in this issue

Copyrights & Wrongs

Next article in this issue

Dangerous Liason

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

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Music Technology - Nov 1992

Gear in this article:

MIDI/Mixer Automation > CM Automation > MX-816

Review by Vic Lennard

Previous article in this issue:

> Copyrights & Wrongs

Next article in this issue:

> Dangerous Liason

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