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AHB Keymix

Article from Sound On Sound, July 1986

Who wants a programmable modular mixer and three-band sweep EQ system that offers full MIDI control of channel routing/muting and all fits neatly into a 19-inch rack? "I do!" shouts Paul Gilby. Read why...

As mixer automation begins to fall within reach of even the most humble studio, Paul Gilby takes a look at one of the first rack-mount systems on the market - the AHB Keymix.

Understanding the need for a piece of equipment is often a cut and dry situation when the merits are obvious; if they're not, then there's a chance you might miss out through no fault of your own. Some products leap out at you and others don't. The Keymix from Allen & Heath Brenell lies in the second category.

The idea of a mixer fitted with MIDI may not seem to be worth a second glance if you've never worked with anything that's got MIDI on it and this is particularly true of many 'recording personnel'. However, if you're a keyboard player, MIDI should be familiar ground, so the benefits of a MIDI controlled mixer should be more obvious and certainly more exciting.


Imagine a typical mixdown situation in any size studio, 4-, 8-, 16- or 24-track. You don't have any automated mixing facilities and you are about to mix a multitrack tape down to a stereo master. On the studio's mixer you have three effects sends and a mute switch per channel and your effects are limited to just one reverb, echo and chorus device.

As you're a fairly hi-tech oriented studio, you're already probably into syncing drum machines and sequencers to tape either with a simple sync-to-tape device or a more flexible SMPTE timecode system.

The mixdown begins. Tape counter positions or timecode readouts have been written down for the various events that are to happen throughout the song. You have a keyboard track which plays all the way through but you've now decided that you want it to play on the verses only and it also needs an effect on it. So you note down the points at which to mute the keyboard channel. The reverb effect you have is spending most of its time processing the drum sound but you want to add echo on the last snare beat of the song as well. Not too difficult, until you remember that it will only sound right if you kill the sound of all the other instruments a fraction of a second before that snare beat. Then you ask yourself, 'can I do that and have I got enough fingers to press all the mutes or do I need a helping hand from somebody else?'.

It all sounds very tricky, but it's the sort of situation you often find yourself in when mixing and there's definitely no way you're going to let the fact that you haven't really got enough effects units, or for that matter hands, stop you producing the results you want. But it's all too often the case that you mess up a mute or you're not fast enough at turning the echo send up and so it's back to the beginning for yet another attempt.

The Keymix avoids that scenario and helps you achieve all the routing and muting of channels and effects with precision, time after time. This leaves you free to concentrate on the subtleties of mixing the overall levels rather than worrying about when to switch the effects on or off.

Now that may not sound particularly stunning, but when you actually mix down with the added semi-automation that the Keymix gives you, creativity seems to start and the struggle of mixing to the pace of the music stops. The improvement is obvious.


The Keymix system is a straightforward mixer that has been broken down into separate sections, each housed in a 19" rack-mount unit.

The KM1 forms the heart of the system and incorporates eight input channels and, as the concept of the mixer is a modular one, it's not surprising to find that the KM2 has been designed as a slave unit that allows you to expand the system in groups of eight input channels. This is done by daisy-chaining KM2 slaves to each other up to a maximum configuration of one KM1 master and three KM2 slave units, which results in a total of 32 input channels.

Within the system you can also add up to four KM3 units, each of which offers eight channels of three-band sweep equalisation (more of that later).

The final system component is the KMR remote control unit. It's here that the control of signal routing/muting from input channels and effects sends takes place, together with the programming and storage of events - in other words, it's the brain of the system!


None of the mixer sections of the Keymix system offer unknown territory to those who have used even the simplest of mixers before. The KM1 master unit is an unassumming 8 into 2 mixer with each channel offering Input Level control and Pan, two Auxiliary (effects) Sends A and B (each is programmed to route the signal from the input channel to a desired Aux Send, but not necessarily the same one), an Aux Return Level with Pan and a single switch which allows Aux Send B to derive its signal from the main input channel as would be normal, or from the Aux Return, so permitting further processing or routing of an already processed sound. Around the back there's a stereo jack insert point on each channel for patching in the KM3 EQ or anything else.

Completing the KM1 input channel are a couple of peak LED indicators (red) to check the signal levels and a couple of mute status LEDs (yellow) to let you know if the channel is on or off. Of particular interest here is the peak LED for the Aux Return. It's nice to see this feature as it helps enormously when setting up return signal levels and keeps the risk of clipping under control. Why don't more mixers have them?

At the right-hand end of the KM1 is the stereo output section and this offers level control for both the main stereo output signal and the headphone monitor. There's a mute switch to knock off the main output but this doesn't affect the headphone feed, so it's useful for setting up mixes before unleashing them onto the main stereo mix. Finally, there's a pair of VU bargraph meters to check the overall signal levels.

Returning to the KM3 equaliser, as mentioned, it offers eight channels of three-band EQ using dual-concentric knobs (sweep range and cut/boost) with good overlapping sweep frequencies that range from 40Hz up to 15kHz across the low, mid and high controls. There's also a handy EQ bypass switch for doing just that.

On the rear is a stereo jack socket marked 'Patch' to allow the KM3 to be linked via one cable directly into the master KM1 unit's insert point. Alternatively, you can use the normal in/out sockets if you wish to patch the equaliser into the system after the signal has passed completely through the KM1.

Well, having dealt with the mixer section, it's time to look at the KMR remote control and see what the Keymix system can actually do.


The KMR forms the central control for programming and storing all the Keymix patch configurations and also provides the means by which MIDI or Sync 24 clock information can be used as part of a sync-to-tape facility which in turn opens up the possibilities of automated mixdown.

Within the KMR software there are four main operating modes and these are divided into write modes (which cover Route and Mute information) and performance modes for MIDI and Sequence data.

Any changes programmed into the KMR are immediately stored in its RAM pack so that you are able to keep a permanent record of your patch configurations for recall at a later date. All the information may be displayed on the KMR's large, back-illuminated LCD readout.

Route Mode

As with any mixer, a flexible routing system is essential if you're going to be allowed maximum creative use. Unlike other mixers, the KMR directly controls the routing via its software rather than using mechanical hardwired switches. This means that all routing is 'soft' and therefore totally programmable.

In programming a channel route, you select which route memory (00 to 99) you want to store the information in, select the mixer channel (1 to 32) and then you decide which Aux Send (1 to 8) you would like to send the signal to. Now this is where the differences between a normal mixer and the Keymix become apparent. Usually you would send a signal from, say, mixer channel 1 out on its Aux Send which may have a reverb unit connected to it. With the Keymix, channel 1 doesn't necessarily have to go to Aux Send 1, it can be routed to Aux Send 5 instead which may have a digital delay connected to it. The beauty of this system is that you are able to programme a route memory so that channel 1 in memory 1 is routed to Aux 1 (reverb), but then for memory 2, channel 1 can be routed to Aux 5 (digital delay) and so on. The benefit is that you can share a small number of effects units amongst all the input channels and no one channel need ever be tied-up to any one effect. That's flexibility for you!

Now if that isn't enough, AHB have in fact provided two Aux Sends (A and B) per channel and each has its own level control on the KM1 mixer. Therefore, not only can you route the signal to different effects at any time, but you can also have the sound in a mixer channel going out to two entirely different destinations via Aux A and B.

Mute Mode

The muting aspect of the KM1 mixer is as flexible as the routing of channel signals. There are two points at which the signal may be muted: at the main input to each channel, and at the Aux Return input. If a mute is selected, a LED next to the relevant Input Level control illuminates to reassure you that there is actually a signal present though you can't hear it.

Programming of mutes is done in the same manner as for routing. You choose a mute patch memory (00 to 99) - from a different set of memories - and select the mixer channel you want to mute. Then entering 0 or 1 in the mute data section switches the channel Input and Aux Return off or on respectively.

Muting combinations of these two points gives you total control over whether you want a sound (channel) in the overall mix, and if so, whether you want to hear it with an effect on or not.

Creatively, this facility could be used to mute any extraneous noises that have leaked onto a vocal track; or to patch a snare sound into a channel, process it through a reverb unit and then control the points at which you want to hear the reverbed snare. There are any number of possible uses where fast muting of channels and effects are required.


The idea of computer-controlled routing and muting has been well applied within the Keymix, however, the inclusion of MIDI really brings the system to life.

Once you have programmed all your routing and muting patches you can move on to the MIDI mode. Here, as with route and mute, there are 100 memories available (00 to 99). When you enter MIDI mode, two sets of information are required - Data 1 and Data 2. Data 1 asks you to specify firstly, which internal patch number (00 to 99) you wish to store the MIDI information in, secondly which MIDI channel (1-16) data is being received on, and thirdly which MIDI program number sent from an external keyboard corresponds to which internal MIDI patch number on the KMR.

Once you have specified all that, you enter Data 2 and tell the KMR which route and mute patches the MIDI data will select eg. pressing program number 8 on a JX-8P synth will select MIDI patch number 8 in the KMR and in turn will select route 8 and mute 8. The result of this action could be that you switch an echo unit into the signal path to fill out the JX-8P's sound. It's worth pointing out that the program, patch, route and mute numbers don't have to be the same; you may wish to select, say, program 4 on the synth and have exactly the same echo effect on it and then combine that with some reverb. It all comes down to how you programme the routing and which MIDI patch number is assigned.

The ability to control which patches are selected and, therefore, when the Keymix is to route and mute signals, means that by using an external MIDI sequencer you can change patches automatically as the music progresses. The whole system could be driven by a master clock (eg. a drum machine) and events such as switching off an echo during the middle of a song could happen exactly when you wanted them to. And, more importantly, because the event is programmed into the KMR's memory, it's repeatable.

Sequencer Mode

This is the final mode and forms the second level of automation within the KMR unit. The idea of external patch changing from a MIDI keyboard as previously described, ties up one of your instruments with the chore of just sending the MIDI program numbers into the KMR whenever a change is required. So, to avoid wasting the capabilities of a valuable instrument, the KMR houses its own event sequencer to allow these changes to be pre-programmed by the user.

In Sequencer mode as in MIDI mode, two sets of data are required after the initial sequence condition has been set. You must first specify which of the 8 clock modes you want to have drive the system. The available choices are:

Manual - ie. step only
Manual step via footswitch
Internal Clock (29-320 bpm)
Sync 24 - where an external Roland-style clock pulse can control the KMR tempo
MIDI - where an external MIDI clock can control the KMR
Internal Clock Record - same as the normal internal clock except that it acts as a free-running, real-time event recorder and remembers an event each time you press the footswitch
Sync 24 Record - same as above but uses an external Sync 24 clock
MIDI Record - uses an external MIDI clock with real-time footswitch programming of event points.

An added bonus of the clock selection is that it converts timing data from Sync 24 clocks to MIDI timing data automatically and it also generates MIDI Song Position Pointers.

Two further sequence conditions need to be set next - the tempo, and the sequence song number ie. which of the 10 sequences you want to programme (0 to 9). In setting the tempo, you're asked to enter a number between 19 and 99 that corresponds to a beats per minute (bpm) value. This is due to the KMR display only being able to handle two-digit numbers. A conversion table is therefore included in the handbook where you'll find that 19 = 29 bpm, 20 = 30 bpm, 21 = 33 bpm and so on. I didn't like this compromise as it also forces you to be satisfied with a tempo resolution of between 1 and 5 bpm when using the KMR internal clock. However, it's not a problem when an external clock is used as the resolution is infinite.

Moving on to further Sequence mode information, Data 1 asks for the sequence step that is to be programmed (step 00-99), the bar number and the fraction of that bar. The best way I found to programme the last two pieces of data is to set the KMR for Internal Clock Record and punch in the tempo. This clock mode pre-supposes that a footswitch is connected, so instead of having to work out which bars and on what beat you want an event to occur, you just press the Start button (a red LED flashes to indicate the tempo) and as the music plays, you hit the footswitch each time you want an event to happen.

Starting from sequence step 0, the first three steps could read like this:

00 04 01
01 08 24
02 15 90

The KMR's sequence mode defaults to a 4/4 beat with 24 ppqn (pulses per quarter note) and the fraction (1-96) defaults to 1 (24 x 4 beats = 96). You can see from the above table that step 02 of the sequence will occur at bar 15, fraction 90 ie. just before the 16th bar.

This is typical of the type of data that you would need to enter if you were going to switch on an Aux Return just prior to a snare beat that you want reverb on. The fraction number is of course directly proportional to the tempo and so when the tempo is slow the point at which you switch the status of a Keymix channel will have to be closer to the event ie. 95 (that's about as close as you'll ever get to the 96th fraction!).

The beauty of using the Internal Clock Record mode is that having tapped in the points where you want events to happen, you can then edit them if you were slightly out in your original timing.

Having programmed the event points you obviously have to programme what you want to happen on those points and this is done in the Data 2 mode. The events we're interested in are, of course, the routing and muting of effects and channels. It's at this point that you need to remember which memories the particular routing/muting configurations you are going to use were stored in, so it's worth keeping a written note of them in the first place. Having made your decision, all that remains is for you to programme into Sequence Data 2 a route and mute number for each sequence step. As with Data 1, you can always edit the information later.

Hopefully you can see that with this degree of flexibility, the Keymix will allow you to home in on any point of a song - right down to a fraction of a beat. Events can be as complex as you like and they'll be executed on the step every time.

The creative application for this sort of facility is quite amazing and can transform a very limited number of effects units into what sounds like dozens. When you start to incorporate the newer MIDI controlled effects such as the Alesis MIDIVERB which enable selection of reverb memories over MIDI, then the automated switching of channels and effects returns by the Keymix will, in combination with MIDI keyboards, a sequencer and drum machine, provide a very powerful music-making environment with unparallelled control over almost every aspect of sound creation and mixing.


The use of sync-to-tape devices is now spreading very rapidly from the top-end studios to 16-track and 8-track users. Other than the obvious application within an electronic music studio, these devices are likewise making an impact on the audio-visual studio.

To fully exploit the potential of its automation facilities, the Keymix really needs to be used in conjunction with a SMPTE-to-MIDI convertor such as the well-established Roland SBX-80, the Fostex 4050 or the marvellous new Bokse SM-9. Any one of these devices will read a SMPTE timecode recorded on a multitrack tape and pass accurate timing information onto the same unit's MIDI output which can then drive a sequencer connected to the Keymix. This system would allow you to run back and forth along the tape with the programmed Keymix events being locked to the exact point at all times.



All inputs unbalanced
Stereo output balanced +4dBv
Frequency response 20Hz to 20kHz
Noise -71dBv (DIN 20kHz B.W.)
Crosstalk better than 60dB
Distortion 0.05% THD


High Frequency +/-15dB across 5kHz to 15kHz sweep
Mid Frequency +/-12dB across 300Hz to 6kHz sweep
Low Frequency +/-15dB across 40Hz to 400Hz sweep
All inputs/outputs unbalanced
Noise -75dBv (DIN 20kHz B.W.)
Maximum output +22dBv


Sync24 in/out


100 Effects send route patches
100 Input mute patches
100 MIDI programs
10 Song sequences
100 Steps per song
Step or Real-time event programming


KMM Instant RAM pack


For the price, the Keymix is most certainly a welcome system. The inclusion of MIDI control is crucial to the development of a functional automated mixdown set-up, and in this case the option of control via MIDI program numbers or MIDI timing data has been well thought out and offers enormous scope.

As with any system, there are negative aspects and the Keymix has a few, though these are mainly concerned with the KMR remote control. Due to the way the KMR has been designed, the LCD will only show a two-digit number for any parameter - probably as a result of the software. It is one thing to introduce a new mixing system to the recording fraternity, but in doing so you must surely make it as easy as possible for people to understand the merits and use of the equipment. Two main points stand out. Firstly, using an arbitrary value to correspond to the real tempo of the built-in sequencer is frustrating, though not the end of the world. Secondly, limiting the MIDI program numbers to 100 means that you have to transfer programs on your keyboards from higher memory numbers in the 101-128 range down to a number between 1 and 100, whilst also having to remember that the Keymix counts from 0 not 1.

The criticisms levelled are centred around the fact that the KMR unit has been squeezed by both software and hardware constraints. The Keymix system, however, is also available in another version without the KMR. This uses the Keymix KMI64 interface and more comprehensive software to run on a Commodore 64 computer. Additional benefits of this larger system include a greater number of mute patches and sequencer event storage, a channel index which lets you name each sound source connected to the KM1 and KM2 units, a further KMS64 interface for drum machine synchronisation, and more...

The final point, and the question you are all probably asking, is where does the Keymix fit into an existing system? Well, it could be used as part of a live keyboard mixing set-up if you wanted, but would perhaps be better suited to those who want an affordable element of automation within the studio. You should have noticed from the photograph by now that there are no faders on the Keymix. This is because the Keymix is not meant to replace a conventional mixer, but rather expand its capabilities. Who knows, maybe AHB have an automated fader option in the pipeline? In the meantime, take a serious look at the Keymix.

Keymix system: KM1 Master with KMR Remote Control and RPS1 Power Supply £1413.04; KM2 Slave £725; KM3 Equaliser £410; KMI64 Interface £130.39; KMS64 Interface £73.91 and KMM RAM Cartridge £35. All prices exclude VAT.

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Publisher: Sound On Sound - SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.

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Sound On Sound - Jul 1986

Donated by: Gavin Livingstone

Gear in this article:

Mixer > Allen & Heath > Keymix

Review by Paul Gilby

Previous article in this issue:

> Totally Musical

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