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Mark Of The Unicorn 7S

MIDI Mixer

MIDI has been slowly creeping into mixing desks for some time now, but this American mixer goes all the way. Vic Leonard mixes with MIDI.

The power of MIDI allows an unassuming rackmount from the US to be a fully-automated mixing desk - strange but true.

WHERE MIDI AUTOMATION of mixing desks is concerned, MIDI is normally used simply to mute individual channels, and sometimes effects sends on the desk. Of course, much more sophisticated automation is possible. SSL desks, for example, have "total recall", a facility by which all settings on the mixing desk can be recalled at the press of a button - but not via MIDI.

MIDI doesn't (yet) fully accommodate mixing considerations - there are no dedicated controllers for EQ, for example. Even where MIDI controllers do exist, there are often problems with real-time control. MIDI Controllers #7 and #10 control MIDI Volume and Pan respectively but often result in "zipper" noise (audible steps in volume) when altered quickly. Although changes to the MIDI spec are currently being considered by the relevant MIDI authorities, currently the only way to change many parameters is via system exclusive - but bear in mind that you can't intersperse SysEx with other MIDI information except MIDI Clock and other System Real Time commands.

So, how do you get a full MIDI control of your mix? Mark of the Unicorn (renowned for their Performer Mac sequencer) have presented us with one option: the 7s MIDI Mixer.


THE 7S CONSISTS of seven stereo audio inputs, each with trim pot, noise gate, bass and treble EQ, volume and pan. With the exception of the gate threshold and trim, all controls can be configured via MIDI. There are also a pair of mono inputs with MIDI control, although their output is not summed with the stereo outputs but emerges via individual outs. Furthermore, there are two effects sends and returns and a Chain in/out for additional 7s units.

The mixer is a typical 1U-high rackmount with the front panel headings in bright orange, as are the larger rotary controls and logo - it certainly stands out amidst other rackmount equipment. The front panel houses the trim pots, the four effects sends/returns and an LED to show the state of the noise gate for each channel. Gate Threshold, Master Output Level and Headphones Level are controlled by three, larger rotary controls. On/Off - nice to see this on the front panel, not the rear - headphone socket and a pushbutton for setting the MIDI channel of the 7s complete the panel.

The rear panel is socketland. Sixteen mono jacks for seven stereo channels and the main outputs, 16 phono sockets for the effects send/returns, chain in/out and channel 8, and MIDI In and Thru. Admittedly, it's more cost-effective to have the sockets poking through the rear panel rather than bolted to it, but the phono sockets float in a quarter-inch hole and continuous use may result in fractures to the solder connections to the PCB.

Finally there's an 18V DC power in socket - MOTU have had the sense to keep the power supply external to prevent the heat and hum problems associated with internal supplies.

The spec quotes figures of 78dB without noise gate and 90dB with noise gate, which are reasonable, although figures of this nature without any reference information are pretty meaningless. Audio inputs are given as being at line level but this can be anywhere between -20dB and +6dB. If the signal-to-noise figures are measured using a high input level then any system running at a lower level, say the semi-pro level of -10dB, will be much noisier - manufacturers should provide reference figures. Inputs are high impedance (20kOhms) suggesting that the 7s is primarily intended for mixing MIDI instruments.


THE 7S' STEREO inputs suit the current trend of synths sporting stereo outputs. It also allows the 7s to hide a multitude of sins in not having to match the input levels of a pair of mono inputs to create the stereo image - a situation which requires far better resolution than the eight-bit VCAs controlled with MIDI's seven data bytes using interpolation techniques found here. Incoming audio first passes through a pre-amp stage where the trimpot on the front panel lets you set the gain, although in a bit of a haphazard manner. Instead of having a dedicated LED showing the onset of clipping, you have to use the noise gate LED by setting the gate threshold control to three o'clock and rotating the trim control until the gate LED flickers. Unfortunately, there's then no way of knowing whether you're approaching distortion when audio is passing through and the noise gate is being used normally.

The input then passes through the noise gate with the attack and release being controlled only over MIDI. The threshold is the same for all inputs using the gate, and the ability to turn the gate on or off for various inputs is, again, controlled over MIDI only.

Each stereo pair then passes through the EQ stage. No information is given on this, but I'd guess at 100Hz for the bass and 12kHz for the treble - reasonable for mixing MIDI synths. EQ is only available for the stereo pair as a pair - you can't have different tone settings for each side of a stereo pair. Finally, the signal passes through volume (VCA) and pan controls after which the signals are summed for the right- and left-hand main stereo outputs.

It is crucial to have control over EQ, and most budget mixers give a mid-frequency sweep and cut/boost or (preferably) controls for low and high mid. With only two EQ controls, the 7s is best suited to sounds which need little tonal treatment. While limiting, this arrangement should readily lend itself to synths, though perhaps less so to drum machines. The fact that the 7s is MIDI-controlled should not restrict its use to MIDI applications, but a mid-band EQ of some description would have opened up many more doors for the unit.

Channel 8 is odd in that it is made up of a pair of mono inputs with the same controls as for a normal stereo pair, but the output is not summed to the stereo buss. Instead, it's sent out from a pair of dedicated outputs. So you can look at it as being a pair of independent ins/outs.

"With Creator recording, you can switch to the 7s Console, move controls and then switch back to the sequencer with the movements recorded."

There are two Effects Send/Return lines, with front panel, non-MIDI controllable trims for each. Finally, Chain In and Out allow the use of two or more units. This is effectively a send/return circuit without any controls but it could be used as an extra pair of inputs.

There are a total of 20 inputs going to the stereo buss, two inputs going to an independent buss, and a total of eight outputs.


CONTROL OF THE various MIDI-programmable aspects of the 7s is accomplished via MIDI controllers. This method has advantages over SysEx in that it's easier to work with and gives fewer timing problems through shorter messages (three bytes maximum).

However, operating level, pan and EQ for all inputs, effects and so on involves the use of a lot of MIDI controllers. It's possible to achieve this without using Controllers already assigned for other duties, but there is always the possibility of using a currently undefined Controller, which then takes on a duty under a proposal from one of the two MIDI authorities in the USA and Japan. MOTU have used the eight General-Purpose MIDI Controllers, 22 undefined Controllers and the Least Significant Bytes of 16 Continuous Controllers to achieve the 46 Controllers that the 7s needs.

The use of MIDI Controllers means that software can be easily written or adapted to control the 7s. For instance, C-Lab's Realtime MIDI Generator page, Steinberg's MIDI Manager in Cubase and Hollis Research's MIDIman can all be used to control the 7s in real time with their respective sequencers on the Atari ST, and a similar situation occurs with MOTU's Performer. MOTU also supply a program for the Mac and a desk accessory/program for the ST called 7s Console. Hardware devices such as JL Cooper's Fadermaster can also be used, although this only has eight faders available at any one time.

Use of most of the features is obvious, with the possible exception of Smoothing. This controls the speed at which the 7s responds to MIDI data for volume commands, including mute and solo which can be achieved by sending the relevant 0 settings of MIDI Controllers 16 to 23. The higher the Smoothing setting, the smoother the change, but the longer the time necessary to achieve that change. Lower values give a faster response but may mean you can hear the stepping action as a parameter moves between two values.


TO LET YOU take control of the mixer's MIDI functions, "7s Console" is provided. For the Mac, this can either be run as a stand-alone program or in conjunction with a sequencer via the use of Apple's MIDI Manager multitasking environment.

The on-screen image takes the shape of a miniature mixing desk measuring about 75mm by 100mm with 5mm diameter knobs. Apart from the obvious point of having an immediate representation of an item you can recognise, it's difficult to appreciate why it should be in this way - it's too small, you have to make do with very short throw (25mm) faders and also have to move along an imaginary horizontal line to rotate the knobs.

All the MIDI features are here, along with a few extras. "M" mutes the specific channel and is carried out by disabling the Smoothing on all channels, setting the volume for the specific channel to zero and then re-enabling the Smoothing as appropriate. If the Smoothing isn't disabled, the time taken for mutes to occur depends on the current Smoothing value. In a similar fashion, "S" solos the specific channel. This is carried out by again disabling all Smoothing, setting all volumes except the current channel to zero, and then re-enabling Smoothing. This means a total of 30 bytes must be sent (excluding the Smoothing re-enabling) which takes about 10mS. It's a shame that MOTU haven't implemented Running Status for the transmission of MIDI data, as this would have saved nine bytes and so reduced the transmission time to 7mS. As all Controllers operate over the same MIDI channel, there's little excuse for this.

Having set up the various controls, you can then save them as a Scene to be recalled another time. Recall can be achieved by a menu selection, sending a MIDI Program Change to the 7s, or by using the command key and one of the numeric keys for the first nine scenes. One point to note is that a value of zero for MIDI Controller 0 is sent out as the first and last MIDI command for a scene. If this is intentional, it runs the risk of interfering with any MIDI device which responds to MIDI Bank Select (Controller 0) and happens to be on the same MIDI channel as the 7s. This might seem unlikely, but bearing in mind that the Controllers used by the 7s are unlikely to overlap with those used by a synth, it's certainly conceivable.

The Atari ST version differs in several ways. It's provided both as a desk accessory and a program. The DA is large - 107K - which means that you're unlikely to be able to run it with any of the major sequencers on a 1Meg Atari. There's more bad news: if you try running the DA with Cubase, it seems to work the first time you open the accessory, but crashes the second time. However, it appears to work fine with Creator apart from some breakthrough from the bar/beat counter on the Creator screen. The "desk" is slightly bigger - and the knobs can be controlled by moving outwards along the radius of a circle centred at the knob; you aren't restricted to moving horizontally. Why didn't MOTU do this on the Mac version?

"Try a rapid pan and it feels wrong - it's not that it 'steps' across the stereo spectrum; it simply doesn't move in the way a stereo image would."

With Softlink you can have the 7s Console and Creator/Notator in memory at the same time by using the program version of Console. With the sequencer recording, you can switch to 7s Console, move controls and then switch back to the sequencer with the movements recorded. With Steinberg's Switcher equivalent, Cubase/Cubeat and the program version of 7s Console can be resident in memory together, but movements on the Console while the sequencer is in record mode are not recorded.

There are another couple of interesting features. The settings for a scene can be saved to a Standard MIDI File (appears to be format 0), and loaded into a sequencer to re-create that scene. It appears to load at bar 1, beat 1 but can always be moved to where the scene change is needed. Again this feature doesn't appear on the Mac version. Also, you can set a SMPTE time for a scene change to take place, but I couldn't get this to work - I suspect that MIDI Time Code is needed, which wasn't available for the ST I was working with. More to the point, the only program supporting MTC is Cubase, which won't work with the DA. Unfortunately, there was no manual for this DA, or Read Me file on disk. A shame.


THE BIG QUESTION: how well can the 7s perform in a practical situation?

First of all, noise. Without the noise gate in the unit is noisy - certainly more so than other rackmount mixers or budget desks, but you're unlikely to use it without the noise gate in operation. More to the point, most MIDI synths are noisy with a capital N and, for these, the usefulness of the gate cannot be underestimated. It's the equivalent of having a number of single-ended noise reduction units to hand. It would have been nice to have had individual control over the gates for each channel, and I was rather concerned that setting the gate for the noisiest synth would cause transients on a less noisy synth to be lost, but in practice this problem didn't arise.

Using the volume and pan controls isn't difficult with the Console program or via Cubase's MIDI Manager or other sequencer equivalent. You can't program the solo and mute facilities in Cubase, because you can only allocate one MIDI Controller to each control on screen, but you can still set up the volume, pan, EQ, effects and smoothing controls with ease. This certainly would not be so if MOTU had used SysEx for data transfer.

In use, the smoothing control is necessary if levels change rapidly when a signal is being processed as the level changes. That said, you can use a low value for smoothing (4 or 5), giving fast response and little or no extraneous noise. There's always going to be a trade-off between speed of parameter change and the audible effect of those changes taking place, but as long as the changes are not too drastic the audible effect can usually be ignored.

Using scene changes on the 7s Console is a different matter. You need a fair bit of space in a song to send the relevant changes for a scene; it's difficult to estimate but it's probably the best part of half a second. This can't be down to the transfer of MIDI data, so you have to assume that the 7s mixer has to "digest" the data. The changes are certainly noticeable if audio is being processed; a case of mild indigestion, perhaps?

Using the MIDI Manager page on Cubase, it was possible to completely automate a MIDI mixdown for a radio advert I was working on. This included using changes to the smoothing to give a slow(ish) attack feel on a synth I hate programming, and various subtle changes to the EQ. Even without a mid-band EQ control, you can still achieve a degree of subtlety in tone change by using the treble and bass conservatively. Similarly with the pan control - try a rapid pan and it feels wrong. It's not that it "steps" across the stereo spectrum; it simply doesn't move in the way a stereo image would if you controlled it with a rotary knob. You can route the main outputs through channel 8, however, and then have control of the overall level via the MIDI Controllers. It certainly beats trying to do a smooth fade-out of all the audio by turning the front-panel knob.


THE 7s MIDI Mixer uses MIDI technology in a way that's most interesting. By using stereo controls, MOTU have removed the problems of trying to use mono controls through eight-bit VCAs (insufficient resolution for precise control). It offers 22 inputs and 10 outputs, including effects sends and returns, and minimal EQ - certainly on a par with many rackmount mixers of this price. However, the lack of clipping LEDs and the manner of fixing for the phono sockets show some of the hardware corners which have been cut.

It's sometimes interesting to assess equipment along the lines of "if the manufacturer had increased the price by £100, what extra could have been added?". Mid-band EQ? Probably, although there's then a real problem of being able to allocate sufficient MIDI Controllers to run this over MIDI.

Mono inputs? I doubt it. Overcoming the problems in this area would be likely to cost substantially more than a ton.

All in all the 7s is worth considering if you're eager to automate your system beyond basic channel muting. I wouldn't recommend it to anyone as a replacement for a fully-specified mixing desk but I'd be happy to have it patched into my audio patchbay to deal with those noisy synths.

Price £590 including VAT.

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


Music Technology - Nov 1991

Gear in this article:

Mixer > Mark of the Unicorn > 7S

Review by Vic Lennard

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