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CM MX816 Console Automation

A cost-effective VCA mix automation system that can be used with any console.

Mixer automation need not cost the earth, as Derek Johnson discovers when he checks out this fly-by-wire, MIDI-controlled modular system.

Automated mixing systems have followed the now-familiar evolutionary path of offering more and more facilities for less and less money. The majority of the low-cost units are based around MIDI-controlled VCAs (voltage controlled amplifiers), DCAs (digitally controlled amplifiers) or switchable resistive networks of some kind. The basic principle of such systems is simple — MIDI continuous controller messages (recordable into MIDI sequencers) are used to control the VCAs; the fact that graphic faders can be displayed on a computer screen means that hardware faders are often unnecessary.

CM Automation designed their system around dbx VCAs, which offer acceptably low noise and low distortion performance at reasonable cost. The result is their MX816 — a modular system with a clean analogue audio path and a fast response time, ensuring that the VCAs will keep up with the fader movements. Indeed, claimed response time is just 3 milliseconds per channel, with all 16 channels capable of changing status in under 30ms. The MX816 can be used with any mixer, via the mixer's insert points, or placed in-line between the outputs of a multitrack (or other sound source) and the inputs of the desk.

To use the MX816 effectively, you need a software sequencer with on-screen faders (for example, Steinberg Cubase, C-Lab Creator, MOTU Performer — a longer list is provided in the manual), or a hardware MIDI fader unit such as JL Cooper's Fadermaster. You can use it without either of these if you have a smart master keyboard with assignable controllers, but this approach is less than ideal.


All the audio connections, which are unbalanced, are at the rear of the 19-inch case, and come in the unusual but compact form of phonos. The unit I had for review had eight inputs, eight outputs, one summed output, MIDI connections (In and Out/Thru), and a power socket for an external 9V supply. I'd rather have had an internal supply, but I guess cost comes into it; use an external supply, and your unit can be used anywhere with no modification other than using a different power supply. There is also a ground lift switch, which helps avoid ground loops and the hum problems they cause. The only inelegant thing about the review unit was the strip of black tape that covered the holes needed to expand the MX816 to full 16-channel operation.

The front panel of the MX16 is minimalistic, since this is almost wholly a software-controlled device. Thus the only controls on the unit are the four momentary switches on the left of the device's front panel. These switches are labelled Mute, Max, Patch and Fade, and each has an attendant LED. Mute is the most obvious button: pressing it mutes all channels, and pressing it again unmutes them. Max is also pretty self-explanatory, since pressing it opens all the VCAs to full gain — do this when no sound is present, or you could be in for a shock! Restoring all previous settings is simply a matter of pressing Max again. Patch and Fade perform different functions depending on what you're doing programming-wise.

Inside Story

Control of the MX816's VCAs is undertaken by assignable MIDI controllers. In most cases, where the user has a computer at the heart of the system, the MX816 can be controlled from the 'virtual' faders and switches provided as a part of many of the leading sequencing packages. The real, physical faders on the mixer should be set at or near their 0dB position in order to optimise the gain structure of the signal path. Thankfully, CM Automation take the pain out of the task by explaining how best to use their system with many of the leading sequencer packages. The software for which details are given are Dr T's Beyond (Mac); Dr T's KCS with Automix (Amiga); Steinberg Cubase (ST — with MIDI Manager); C-Lab Notator/Creator 2.2 (ST); Mark of the Unicorn Performer 3.3 (Mac); and Opcode Vision 1.1 (Mac). For example, on Cubase, if you've never used MIDI Manager, the instructions are as good as a tutorial, with all the hex code necessary spelled out in detail, with precise instructions on where to use it. Any software that provides on-screen faders can be made to operate the MX816 and, in the case of software not covered by the manual, the explanations for other software should point you in the right direction.

Besides being able to act as a real-time fader unit, the MX816 can also store 'snapshots' as patches. A snapshot contains a scene of all the fader settings at a particular time. Using MIDI program changes moves from scene to scene, and there is even a programmable fade time between scenes, which helps avoid abrupt level changes. This is less memory intensive than continually recording fader/MIDI controller information, and is a good compromise for less complicated mixes, or where sequencer memory is limited, since you can set up to 100 different snapshots and simply switch between them. The scene fade time is 0 to 30 seconds.

In the first instance, getting the MX816 to understand how you want it to interact with your sequencer can be a bit tricky, but it only really needs to be done once. First of all, connect a device capable of sending MIDI Continuous Controller information (your computer running a software sequencer, or a hardware fader unit) to the MIDI In socket of the MX816. Press and release the Fade button: the Fade Status LED will flash. Now move your first fader. The MX816 now recognises that MIDI message as the one which will control audio channel 1. The rest of the internal channels will respond to the controllers numbered consecutively from that controller. If, for example, you send it MIDI Controller number 7, that will control channel 1, MIDI Controller number 8 will control channel 2, and so on. It stands to reason that you'll have to make sure that your fader unit, or software, is configured accordingly. Up to 17 controllers are assigned, even though there are only a maximum of 16 VCAs on a single MX816. What is the 17th controller for? Fader 17 is the 'Joystick Controller', which allows the Snapshot scene patches to be manually panned (their word — I would prefer to use crossfaded). This is especially useful in a live situation, where the operator could crossfade between several different effects setups. The programmable fade time applies here, and again makes for smooth transitions. The crossfade moves between the current patch and a new patch and from the current patch to the old patch, giving three patches (or scenes) altogether.

Editing can, in general, be a little inscrutable, and it is here that most of my complaints would arise. For example, changing the fade time (for transitions between snapshots) involves pressing the Patch button, then pressing any MIDI note on your keyboard once for each second you'd like the fade to last (press four times for a fade of four seconds, for example), and pressing Patch again. This is simple and works perfectly well, but isn't exactly intuitive.

"At less than £350, the 8-channel MX816 is one of the cheapest ways of adding MIDI-controlled automation to any system."

The MIDI Out socket normally functions as a Thru, passing note events, program change commands and continuous controllers; other information is apparently ignored, which could be good — MIDI filtering at no extra cost — or annoying, depending on how you wire your MIDI system. It's best used only to chain other MX816s or similar devices. The MX816 can also send a System Exclusive dump when required. Such a dump contains the fader and mute setup tables and the 100 snapshot scene patches.


An 8-channel fade/mute system on its own is unlikely to meet the needs of a large studio, though it could still be used to control group levels, effect sends and returns or particularly tricky channels. For the more sophisticated user, multiple MX816s would be quite a cost-effective option — a fully packed MX816 will offer you fader control at a little over £36 a channel. If you've got a 32-channel desk, or your inputs and aux returns add up to 32 inputs, then two MX816s are still economically viable.

In MIDI-based studios, the MX816 could also be really handy: a lot of synth modules and other sound sources offer a great deal in the way of separate outputs and/or built in effects. If you use MIDI controllers to alter the apparent level of the sound, you may be aware that the outputs do not actually go completely off, and in any event, there may be a significant amount of residual noise. Connecting the outputs of the offending synths to an MX816, on the other hand, will allow true volume control and true muting. The potential outputs from more than a couple of multi-timbral sound modules soon mount up, making the MX816 quite a worthwhile and cost-effective way of freeing up inputs on your main desk, since it doubles as a simple sub-mixer. This is only useful in situations where no EQ, aux sends or panning are required, but it's better than nothing.

There was talk earlier in the review about hardware fader units: you may be interested to know that CM Automation make two such devices themselves. The FX-100 features eight 100mm faders; its little brother, the FX-60, is a more compact unit with 60mm faders. Both feature eight mutes for each channel, and two or more units can be linked to access 16 or more channels. Expect the FX-60 to be priced at around £200, and the FX-100 a little higher. Naturally, either of these units will be well-suited to controlling the MX816, and the word is that UK distributors AMG may be offering specially priced packages of an MX816 and FX-60/FX-100.



S/N ratio 98dB
Dynamic Range 106dB
THD <0.01%
Frequency Response 10Hz-30kHz
Attenuation > 98db at 1kHz
Noise level > -95dB
Input impedance 20k0hm
Output impedance 150 Ohm

Overall, the MX816 delivered as promised. The sound quality is both clean and quiet, as is expected from dbx VCAs, and I can also reveal that I heard no clicks when using the mutes. The system is both straightforward and open-ended — you can start with eight inexpensive channels and upgrade later.

For less than £350, the 8-channel MX816 is one a the cheapest ways of adding MIDI-controlled fadei and mute automation to any system — MIDI Muting alone can approach this price. The ease of use oi the system is largely determined by the sequencer package with which you use it and, especially when editing or amending mixes, this can make quite a difference. However, with most of the packages that offer a 'virtual MIDI fader' page, the system should prove very effective.

Further Information
MX816 8-channel version £345; 16-channel version £579; 8-channel expansion £235.

AMG, (Contact Details).

Also featuring gear in this article

Previous Article in this issue

Soft Centres

Next article in this issue

MIDI - The Absolute Basics

Recording Musician - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.


Recording Musician - Sep 1992

Donated & scanned by: Mike Gorman

Gear in this article:

MIDI/Mixer Automation > CM Automation > MX-816

Review by Derek Johnson

Previous article in this issue:

> Soft Centres

Next article in this issue:

> MIDI - The Absolute Basics

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