The idea of marrying MIDI with an audio mixer is by no means new, but AHB's Keymix is the first MIDI mixing system to be made generally available. Is the marriage a successful one?

For this writer, the concept of a MIDI'd mixing desk has seemed a bit of a nebulous one for some while now. I mean, how are MIDI and your typical mixer going to interact in a meaningful way?

The possibilities seem plentiful, but until Allen & Heath Brenell delivered the goods with their Keymix system, I'd yet to see a MIDI mixer work properly, let alone decipher what, precisely, was going on between the interface and the machine it was stuck to the back of. What AHB have opted to do with Keymix (and their CMC24 and CMC32 mixers, incidentally) is to use MIDI to store input muting and effects routing settings for up to 32 input channels, which can then be recalled as patches from a MIDI instrument or sequencer, or as events recorded into Keymix's internal sequencer.

Keymix has applications both in the studio and on stage, but it's in the former setting that it will most likely find its home. Mixdown automation in some form or other is becoming an increasingly common feature in studios nowadays, and in a studio which makes regular use of MIDI instruments and sequencing, this is the sort of role that Keymix will assume.

With Keymix slaved to a MIDI sequencer, which is in turn slaved to a master SMPTE timecode track on tape, you have a very precise means of controlling the muting and effects routing of an entire MIDI instrument setup (which of course can include synths, samplers and drum machines).

Keymix isn't intended to replace a standard mixing desk, but rather to take on (by effectively automating) some of the tasks that the engineer is presented with on mixdown.

AHB have designed Keymix as a modular 19" rack-mounting system, consisting of the KM1 eight-channel master mixer, KM2 eight-channel slave mixer, and the KM3 equaliser which offers eight discrete channels of three-band equalisation.

The maximum configuration consists of one KM1 master, three KM2 slaves daisy-chained via multi-way connectors, and four KM3 equalisers which are patched into the mixers, making a total of 32 input channels with equalisation for each channel. But Keymix's modular format allows you to start with just the master mixer and build up the system as and when required, which is no bad thing in this day and age.

The designers have provided two alternative options for controlling the routing/muting of signals: the KMR dedicated remote controller and the KMI64 computer interface. Both of these plug into the KM1 master mixer. The KMI64 consists of cartridge-based software which runs on that old workhorse, the Commodore 64. But more on these later. First, let's look at the mixer and EQ units in more detail.

The KM1 master mixer unit consists of eight input channel blocks, each with two inputs feeding a master stereo mix output. Each block consists of the main channel input, two auxiliary send controls labelled A and B, and an effects return input. On the front panel are dual concentric controls governing level and pan of the main input and return input in the stereo mix, together with peak and mute LED indicators for each input (the latter is handy for seeing at a glance what channels are muted), and dual concentric controls for the level of sends A and B. There's also a pushbutton control for determining whether auxiliary send B will derive its input signal from the main channel input or the return input, giving you the possibility of switching two outboard effects units into the signal path. The auxiliary sends for each channel are of two types: mono send and return jacks (A) and a stereo insert jack (B).

The master output section consists of two (L/R) balanced XLR sockets which can be used for feeding a front-of-house mixer or a main PA system when used live, stereo and mono output jacks, and a headphone jack.

The XLR signal output is independent of Keymix's master level controls, but usefully, it can be muted at the touch of a button along with the stereo and mono outputs, allowing for headphone-only monitoring at strategic moments. There are also separate level controls for the stereo/mono outputs and the headphone output.

The KM2 mixer is essentially the same as the KM1, the only difference being that as the main stereo output is fed into the KM1, there are no XLR outputs. However, the mono and stereo monitor outputs and headphone output are available for independent monitoring of any KM2 slave, and the output muting has been retained, allowing instant muting of any KM2.

"Background: The KM3 equaliser has been designed to fit within the Keymix system so that each input channel can be given its own three-band EQ, but the unit can be used with any mixing console."

The KM3 equaliser has been designed to fit within the Keymix system so that each Keymix input channel can be given its own three-band equalisation, but the unit can equally well be used with any other mixing console. Dual concentric pots are used for frequency sweeping and cut/boost control in each of low, mid and high ranges, covering a total range of 40Hz to 15kHz. Once again, a peak level LED has been included for each channel. There's also an EQ Bypass switch for each channel, which is handy for making comparisons when setting up a sound.

Rear panel connections consist of mono in/out and stereo jacks for each channel, affording the maximum flexibility when patching the unit into either Keymix or another console.

With the help of the KMR or KMI64, you can define route/mute settings for all input channels and then group these settings into patches which can be called up remotely from a MIDI sequencer track or a MIDI instrument (KMR only), or else entered as events in an internal sequencer which can be set to run according to its own internal clock, an external MIDI clock (KMR only), a Sync 24 input, or tape sync (KMI64 only).

Each control option has its own advantages. KMR's is primarily that it allows you to incorporate Keymix into a SMPTE timecode-based system - which will obviously be appealing to some studios. The most likely chain to accomplish this is MIDI sequencer slaved to SMPTE timecode track on tape (via a SMPTE-to-MIDI converter) and Keymix slaved to sequencer (either through direct synchronisation or by patch selection from a sequencer track).

In contrast, the KMI64 interface option (in conjunction with AHB's KMS64 sync interface) is strictly non-MIDI. What it does allow you to do is record a standard sync track onto tape and slave Keymix's internal sequencer to that. The KMS64 interface also outputs start/stop and 24ppqn clock signals, allowing you to slave a MIDI sequencer to Keymix with the addition of a suitable clock-to-MIDI converter. Then again, slaving Keymix to Sync 24 (which is possible with the KMS interface) and a MIDI sequencer to Keymix (as outlined above) would allow you ultimately to slave the whole setup to a SMPTE timecode track - but without all the advantages that set SMPTE above ordinary tape sync in the first place. You win some, you lose some.

Where the KMI64 option really comes into its own is in the display department. There's simply no comparison between the KMR controller's rather limited LCD and the amount of information conveyed via a computer monitor screen - and in the case of Keymix's multiple routing and muting options, that's an advantage not to be dismissed lightly.

The KMI64 software includes Channel and Send/Return Index pages which allow you to enter (and subsequently see at a glance) which instruments are connected to which inputs, and which effects units are connected to which auxiliary sends. You can also adjust, and see on-screen, the muting and routing settings for all 32 inputs. This ready accessibility (and consequent easy comprehension) of information really is invaluable, so it's a shame AHB haven't combined the visual superiority of the KMI64 option with the MIDI advantages of the KMR option.

By now, though, you're probably wondering what all this muting and routing business is all about. Essentially, Keymix allows you to decide for each input channel block (up to the full 32) whether you want the input signal muted or not (and if so whether at the channel or return stage) and to what effect(s) you want the input signal routed. Complete 32-channel settings can be stored as patches and recalled in an instant. The KMR controller can store 100 mute and 100 route patches, while the KMI64 can store a staggering 1024 mute patches, but only 56 route patches.

Routing requires some further explanation. Normally with a mixer, the effects send or insert is hard-wired, so that channel 1 is always routed to whichever effect you've plugged into the channel 1 send or insert. Not so with Keymix, because although this may at first seem to be the case (each Keymix input channel block has its own effect send/return and insert sockets), the routing of audio signals within each KM mixer unit is actually governed by software. This means you can decide you want the signal on input channel 1 to go not to the reverb unit connected to the channel 1 aux, but to the DDL connected to the channel 7 aux. Routings can only be accomplished to effects connected within each eight-channel mixer, a consequence of making Keymix modular in design.

Once you have your mute and route patches set up, you need to be able to access them in real time. There are two ways to do this with the KMR controller: via MIDI or with the internal sequencer. For MIDI access, you can group pairs of route and mute patches into MIDI patches, which can in turn be set to respond to any incoming MIDI patch number between 0 and 99. The remaining possible 28 patches seem to have been dismissed simply because AHB haven't allowed the KMR to display more than two-digit numbers, which seems a mite unfortunate.

"In Use: AHB have realised that entering event timings as bars and fractions of bars is not a lot of fun, so with the KMR, you can program events 'on the fly' by means of a footswitch."

You can of course call up Keymix's patches in real time from a MIDI keyboard, or record them into a sequencer track for subsequent playback. When using a sequencer in this way, editing facilities are determined by what your sequencer is capable of - and you have to dedicate a sequencer track to Keymix, which could leave you short on tracks, The advantage of this approach, though, is that the structure of your 'Keymix' track can conform to that of the other tracks.

AHB have given Keymix an internal event sequencer and a healthy variety of clocking modes. Thus, for instance, you can enter your patch changes into the internal sequencer, which can then be slaved to a MIDI sequencer (or you can do things the other way round if you want). This way, you free a MIDI sequencer track which might well be needed for something else (like sending patch changes to a reverb unit that you've got connected up to Keymix). KMR will send or read MIDI song position pointers as required by the sync mode, allowing it and other devices to be kept in sync at all times.

The KMR controller also has Sync 24 In and Out sockets, allowing you to slave a non-MIDI drum machine to either the KMR's internal sequencer or to a MIDI sequencer; alternatively, if you're feeling really perverse you can slave KMR and a MIDI sequencer to a non-MIDI drum machine.

The KMR controller's internal sequencer allows you to enter up to 10 'songs' at a time, each with up to 100 events; alternatively, you can chain up to 10 songs together to give you a greater number of events. An event in this context signals a new route and mute patch, and is entered together with timing information which specifies the bar (0-99) and the fraction of a bar (in 96th-notes). This tends to suggest 100 4/4 bars, which may not be enough for everyone's liking, but like I say, you can chain songs together to get a greater number of bars.

KM1's internal event sequencer (which lies in the Commodore 64's memory) allows for a single sequence of 2048 events and the use of time signatures other than 4/4, but it also has a lesser timing resolution (eighth-notes).

If you're using the internal sequencer as master, you're limited to one tempo for each song (or just one tempo overall in KM1's case), which again might not be flexible enough for everyone's requirements. Slaving KMS to a MIDI sequencer might be a better bet here - sequencers such as Steinberg's Pro 16 and C-Lab's SuperTrack allow you to define a different tempo for each 16-track pattern.

Quite rightly, AHB have realised that entering event timings as bars and fractions of bars is not a lot of fun, so with the KMR, you can program events 'on the fly' by means of a footswitch - and this can be done regardless of whether the internal, MIDI or Sync 24 clock is the master. Of course, you then have to go back and enter what patches you want to call up for each event, but life is still a lot easier than it might have been.

And making life easier is (or at least should be) the name of the game with a system such as Keymix, whose main task is to facilitate automated mixdown in a studio. On the whole Keymix has been well thought-out, but it's a shame AHB haven't seen fit to combine the advantages of the KMR and KMI controller options into one controller. Anyone who's prepared to pay upwards of £1500 for just the basic eight-channel mixer will probably not want to avail themselves of the KMI's sync-to-tape, but will be only too happy to take advantage of the quicker operation that the KMI option provides.

As for the MIDI side of Keymix, it provides an effective means of integrating the system's automation features into a broader MIDI sequencing and SMPTE-controlled recording setup. And Keymix's own muting and routing capabilities are further enhanced by the rapid switching of effects settings that's possible nowadays using MIDI control from a sequencer.

Just how AHB's offering will compare with others - such as the forthcoming MIDI mixers from Akai and Toa - remains to be seen, though Akai's mixer should make more settings programmable and will work out a fader 'path' between two settings. Fader automation doesn't come into the Keymix scheme of things, and although it's by no means a cut-and-dried case as to whether such a facility is desirable, it's possible (given the modular character of Keymix) that AHB will come up with such an option in the future.

"Conclusion: With Keymix slaved to a MIDI sequencer slaved to a master SMPTE timecode track on tape, you have a precise means of controlling the muting and effects routing of an entire MIDI instrument setup."

Whatever, Keymix is intended more as an adjunct to a standard mixing console, and that's a role which it seems to perform very well. So if you're in a studio that makes regular use of keyboards, drum machines and MIDI sequencing and you want to investigate the affordable mixdown automation, Keymix is definitely worth investigating.