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A Fresh Mix

CMC 24 Mixer

Article from Electronic Soundmaker & Computer Music, April 1985

On the cheapest computer-assisted mixer yet, the AHB CMC 24. We take a look.

A & HB's new computer linked mixer could be the start of something big. Tony Mills reports.

This mixer is dynamite. Believe it or not, for around £2,900 it offers not only 24-16-2 operation, but also a limited form of computer-based automation and more user-friendly facilities than you could easily shake a stick at.

If you're not familiar with the world of 8- or 16-channel mixers, there's only one major factor you need to know — they're generally overpriced. There are a few exceptions, including Dynamix and Soundtracs models, but usually the price of a studio quality mixer tends to be around five times the price of the parts involved. Imaginative facilities, ergonomic design and polished finish are the exception rather than the rule, unless you've got a few thousand to spend.

The CMC 24 is a complete exception to all this. Confusingly, it looks like a 16-8-2, which it isn't, having 16 group outputs — the channels you see are in-line inputs, 16 complex channels on the left of the mixer and eight simplified ones on the right, all with very smooth ALPS faders. Between these are the stereo outputs, and hidden away somewhere are 16 group outs — adding up to the most compact 16-bus design any of us have ever seen and ideally suited to a converted bedroom or other home studio. Yes, the CMC 24 is aimed at the Personal or semi-Pro studio, and most obviously at the Fostex B16, which offers sixteen tracks on half-inch tape for around £3,000.

This marvellous compactness is a result of A & HB's decision to store the routing assignments digitally rather than mechanically using bulky banks of selector buttons. With a digital memory all sorts of things are possible — but we'll discuss the automation features later.

In the future we may see 16 and 24-channel versions, but all CMC mixers will have channel inputs and outputs accessible from the top, so the mixer can be pushed right up against a wall — the inputs are on XLR's for mikes and otherwise on phono sockets for economy, as on the TEAC and Fostex units. In addition you have jack socket inputs on the underneath of the front panel which are intended for inserting guitars, with the levels carefully balanced to cope with almost any likely input.

Each main channel has three-band EQ with a variable shelf on the top and bottom and a simple sweep on the mid — you can bypass the EQ and each channel has six auxiliary sends which have to be selected in advance, with up to four used on any one channel. The simpler right-hand channels are ideal as effects returns, so you could add stereo reverb, echo and flange simultaneously to a sound should you desire. Alternatively you could use the simple channels to insert the multiple outputs of a drum machine — these channels have just two-band EQ and simpler routing options, but every channel has an Insert point which allows you to plumb in an effect for just one instrument, such as a guitar distortion pedal.

Speed and simplicity

The CMC's designed for speed and simplicity — you can flick from record to remix as easily as from remix to monitor or from mike to line inputs. There are lots of options on the effects send front — Pre- or Post-fader for instance — and channels can be muted or soloed with an LED display where either of these functions is operational.

There isn't enough space to list all the useful features of the CMC here, but if we point out that it's got TWO headphone outputs, a talkback circuit built into the optional LED ladder meter bridge to save a channel, a mini patch field on the rear panel to split or combine signals, outputs for both a cassette deck and reel-to-reel mastering, selectable Pre- or Post-monitor aux sends and much more, you'll get some idea of the number of features the mixer offers.

That's dealt with the conventional mixer functions of the CMC; as mentioned before, the digital memory aspects were initially introduced to save space. Rather than using switches you have to use the top right-hand field of buttons and associated LED's to route the channels to group outputs. At power-up each channel comes up self-routed; you can change this simply by stepping along the group LED display until you're onto the group you want, and writing it into the memory. When you've written all the channel routings and whether they're muted or open you have one complete patch, which can be stored as one of sixteen in the mixer's memory.

You can select any one of the memories in a fraction of a second by hand or using a footswitch which steps from one memory to the next. Remember that you don't actually have control over fades in volume as you would on a huge AMEK or NECAM desk, since you don't have automated faders; however, for a volume change (say for a guitar solo) you could route your channel to a subgroup set at a higher level, then route it back when the solo's over.

Now for the computer bit. A large plug stuck in the side of the CMC gives control over to a Commodore 64 computer fitted with A & HB's CMI 64 interface with associated firmware. The interface is around £200, but at least you don't have to load software every time you use the computer — it's there in a fraction of a second. After the initial setting up displays you come to the Channel Index, which is simply a space for you to list what instruments or band members are connected to each channel. This may seem gimmicky but it's much more reliable than searching for a bit of paper with track details of a piece you've been working on a week earlier!

Route patch

The Function keys of the computer step you onto the Track and Take index, which is similar to the Channel index. Next we come to the business end of the software, the Route Patching page, which controls the channel-to-group assignment. There are 56 Route Patch memories available with odd and even groups listed alternately for your delectation — simply tap in the number of the group you want each channel assigned to, name the patch when it's complete and store it to disk — or to tape if you've got time to kill.

Mutes are stored on another page; you can use up to 1024 patterns with "/" representing Channel On and "*" representing Channel Muted. Simply place the cursor over the channel you want to change and press the space bar to alternate between open and muted — a copy function allows you to transfer large numbers of mutes to save time if you only want to make a couple of alterations.

Mutes can be saved in the same way as routes, but come back from disk marked "Song Name.M" rather than "Song Name.R", so you can use the same song title for your route, mute and sequence information. The sequencer allows you to enter a chain or "events" (mute and route patches) and step them along manually or from an internal or external clock. If you're using a digital drum machine and have an accurate tempo reading for your music you can enter the time signature (4/4 or 3/4 for instance) and Beats Per Minute and the mixer should keep track — but syncing up either to a drum machine or to tape through the interface discussed below will be a little more reliable.


You can step through the patches with the space bar or a footswitch, or set off a short sequence of patches by footswitch for one particularly difficult part of a mix. Sequences can easily be edited to give a new mix, and you have so many available (up to 2048 events) that you could store several alternative mixes of a track on one disk. Trevor Horn look out!

The CMS 24 is the tape synchroniser which connects into the Commodore's User Port. It has Phono input and output sockets for an FSK tape click, a Roland DIN sync socket for drum machines, a metronome click output and a footswitch stop-start socket. The procedure is to lay down a clock on one track of tape before you start recording, or in sync to your drum pattern on the first recording, and thereafter you have a synchronised code for all subsequent mixing changes. You can't jump in on the middle of a mix and expect the computer to keep track (Roland's new SMPTE time code generator could do that for £900) but the effect of seeing all those little lights changing over with no human aid is still quite astounding.

You can't do gradual level changes even with the computer, but even so the CMC is unique in the field of home studio equipment. The Fostex B-16 has already established itself in the amateur, semi-pro and even professional fields, particularly in the field of TV music which often requires close syncing to cues and lots of alternative mixes. To say that the CMC 24 is a gift for anyone already in that field or using a B-16 for any other purpose is the understatement of the century. With the introduction of the first of Allen and Heath's budget computer-linked mixers, we are all in on the start of something very big.

Also featuring gear in this article

Previous Article in this issue

Making Waves

Next article in this issue

All Systems Go!

Publisher: Electronic Soundmaker & Computer Music - Cover Publications Ltd, Northern & Shell Ltd.

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Electronic Soundmaker - Apr 1985

Donated & scanned by: Mike Gorman

Gear in this article:

Mixer > Allen & Heath > CMC 24

Previous article in this issue:

> Making Waves

Next article in this issue:

> All Systems Go!

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