On the face of it, the Audio Logic MT44 gate doesn't appear to be substantially different from most other gates on the market, but appearances can be deceptive...

Audio Logic is the name given to the professional range of products manufactured by Dod of Salt Lake City fame. They build a wide range of studio equipment, most of which are effects and signal processors. This 4-channel gate works on the expander principle rather than as a conventional gate. Most importantly though, it has an extra control output which generates a positive going pulse whenever the input exceeds the threshold, and the duration of that pulse is identical to the time for which the threshold is exceeded, and is independent of the release time control setting. This control pulse may be used to trigger samplers, sequencers and the like and, though many such devices specify a 12v trigger, most will work well enough from 5v.

But not to put the cart before the horse, I'll start at the beginning and look at the way the thing is put together.

Construction

This unit is finished in black with white and red screening and looks tastefully functional rather than overtly flashy. The overall standard of construction is good, with fibre glass circuit boards being used throughout. DBX voltage controlled amplifier chips are used to minimise noise and distortion.

One great disappointment though, was the amount of mechanical hum generated by the mains transformer. This didn't pollute the audio output but created an immense racket which drowned out any real hum which may have crept onto the recording. This criticism has been levelled at other units from this company and, as they are a reputable US manufacturer, I can only assume that this fault doesn't show up on their 110v, 60Hz domestic models and that they are unaware of the problem.

Let's move on. The controls are all located on the front panel and all the sockets are as you might expect, around the back. Apart from the self-explanatory mains switch, the control layout is simple, each of the four channels being identical. Unlike most gates aimed at the professional market, this one has no attack control, presumably because the expander action makes it less prone to clicking when used on sounds with a slowish attack than a conventionally designed gate.

What it does have is a Threshold, a Release and a Ratio control, this latter controlling the amount of attenuation that occurs when the gate is closed (0 to 100dB). This means that you don't necessarily have to use the gate to switch a sound on or off but that you can use it to turn the signal down by a pre-determined amount if this is more appropriate. The release range is from 50mS to 4.7S.

The threshold action is indicated by a red LED and a 3-way toggle switch allows you to trigger the gate via the main signal input or the rear panel Key input, or to choose bypass mode.

"One great disappointment though, was the amount of mechanical hum generated by the mains transformer."

Looking more closely at the rear panel connections, we see that there are four for each gate and all of them are jacks. The input is a stereo jack wired for balanced use but it works just as well with an unbalanced input and accepts signals up to +18dBv with an input impedance of 80KΩ; the output is also balanced. The others are unbalanced jacks, these being Control Out and Key In.

The Key input allows a signal other than the main input to trigger the gate and this is a regular feature on most gates. The Control output we have mentioned previously, and this is a sensible and useful addition that most other manufacturers have seen fit to omit, despite the fact that it is neither a complex or expensive addition.

The output level may be up to +17dBv with an impedance of 600Ω which makes the unit fully compatible with professional studio standards. However, there's sufficient range to allow the unit to work quite happily at the semi-pro operating level of -10dBv.

Operation

I am always a bit wary of gates with no attack control but this one gave no cause for concern. It cut in fast enough not to corrupt the leading edge of even sharp drum sounds (unless the threshold was set much too high), and sounds with a slower attack didn't seem to suffer unduly either. Release worked normally and with a sensible range as did the Ratio control. Generally though, I would use the Ratio control only for creating special effects and set the attenuation to maximum for straightforward clean-up jobs. A sudden drop in level is often just as obtrusive as a sudden cut-off so there is little to be gained by using the ratio control in this way. Of course you may want to keep the background sounds but just reduce the level, an example being an instrument in a live room where you want to reduce but not eliminate the ambience. In this instance the Ratio control is most useful.

The unit is generally easy to use and gives first class results. It tackles any gating problem from cutting out unwanted spill to shortening the decay on drum sounds and is also handy for modifying the envelope of samples; the only thing you can't really use it for is gating reverb as there is no hold time control. This should not however put you off, after all, when did you last see a digital reverb unit with no gated effect already built in?

So far it all seems pretty ordinary, and in many ways it is. However, there are potential problems that show up on even the best designed gates so lets take a closer look.

"Also the control output is such a useful and logical addition that other manufacturers are doing themselves a disservice by leaving it out of their models."

First we have control signal breakthrough. Put a strong signal into the key input of a typical gate with no input signal present and the chances are that you will hear a slight click as the gate opens and you may even hear some of the signal breaking through onto the output. Doing such a test on this gate you do get a little of this type of breakthrough but only if you turn the gain up to a ridiculous amount. I would say that in this respect, the Audio Logic design performs better than most.

Another evil is clicking when the gate is triggered by the input itself but again, this proved not to be a problem, and I've already pointed out that the gate doesn't mess up fast transients which is a vital consideration, especially when treating drums.

The expander action is fairly sharp so in use, the MT44 behaves very like a conventional gate. I think that this mode of operation was decided on so that fewer controls could be used without compromising the performance. If so this has paid off.

Before continuing, it is worth exploring the Control output facility a little more thoroughly. As mentioned, this gives a positive going, 5v pulse useful for triggering external equipment. It's important to remember that the Decay and Ratio controls have no affect on this output pulse's length or amplitude. This Control pulse may be used to trigger samplers, synths or sequencers but, if the trigger pulse is too long, you might be plagued by retriggering. If triggering the gate from a drum sound on tape, for instance, this is not likely to be a problem because the drum sound will be short enough. Other sources, however, may need attention. You can of course shorten the trigger pulse by setting a higher threshold but this could give problems if the level of the sound you are triggering from varies unduly.

Summary

Good gates are indispensable for keeping tracks quiet when no wanted signal is present or for removing annoying crosstalk between passages of music, and to be offered four in one box for little more than the usual cost of two is more than a little tempting. Also the control output is such a useful and logical addition that other manufacturers are doing themselves a disservice by leaving it out of their models. There are occasions on which an attack control would have been handy but for general clean-up work, its absence didn't cause any problems.

My only reservation concerns the aforementioned transformer hum which was worse than a Sumo wrestler's jockstrap in a power station, so do insist on hearing your prospective purchase plugged in before signing over any cash. If by any chance they're all like that, my guess is that Audio Logic will put things right pretty smartly as soon as they read this review. In all other respects it is a very fine and uncomplicated set of gates and at a very attractive price.

The Audio Logic MT44 costs £359.99 including VAT.

Further details are available from: Rhino Music Spares, (Contact Details).