Dave Ward of Gateway Studio takes a look at this new device that can enhance your home recordings.

One of the brightest days in every month is the day on which some new piece of recording equipment arrives on the studio doorstep for review. This month was no exception and it is my delight to tell you about the wonders of the new Stereo Stimulator from Studio Technologies Inc. in the USA.

The object of the AN-1 Simulator is to create a stereo soundfield from a mono source which is as near as possible a simulation of the natural sound that would be heard by our two ears.

Theory

When we listen to a sound in a room of any size, we hear not just the direct sound of the instrument or whatever the sound source might be, but we also hear multiple reflections from all of the different surfaces in the room. If these multiple reflections take some time to decay, then we call this reverberation. Earlier reflections are often of such a short duration that they can produce 'out of phase' components which can cause up to + or -20dB of variance away from a flat frequency response.

The very complex ways in which the direct sound and the reflected sound add and subtract are never the same at any two points in the room and the phase cancellations can be measured to show a 'comb filter' effect similar to the effect that we experience when using digital delays and other time-based processors. An extraordinary psycho-acoustic function of our ear-brain continuum is that we do not hear these comb filters as flanging and phasing but rather the brain sorts out the phase cancellations for us and they manifest themselves as space and depth.

If we were to sample a sound source with a coincident pair of microphones we would be able to sample the sound arriving at the two points without losing mono compatibility. When a mono source is fed into the AN-1, the device uses a small amount of time delay which is coupled with random phase generation. This is fed to phase adder/inverter circuits to recreate two coherent points we would find at a stereo pair of microphones. Although the left-right sensation of coincident mics is not present from the AN-1, the depth and space of stereo miking is conveyed which improves the definition and clarity of the sound.

Another way of putting this is to say that the device creates two randomly spaced comb filters, one for each output channel, which are incoherent with respect to each other thus creating the simulation of space experienced by our two ears.

Description

The device comes in an attractive blue metal box which has two detachable side-cheeks which make it suitable for 19" rack mounting. The device is 1U high. On the front of the AN-1 we find from the left, one control marked 'Stereo Width' which does very much what one would expect and stretches the width of the stereo simulation. The next two controls form a modulation section (Depth and Width) which can be switched out of circuit. There is one other switch which sums the two outputs so that one can check for mono compatibility.

At the rear of the unit are three stereo jack sockets, one for input and one each for outputs left and right. For balanced operation, a standard quarter-inch jack plug is used for both inputs and outputs. For use with an unbalanced system, two standard jack plugs can be used and the low side of the balanced line will automatically go to ground.

Operation

The manufacturers point out that unlike many effects devices the AN-1 automatically adds in the correct amount of clean sound with the effected sound to give the maximum space and depth of stereo simulation.

This means that if one uses an auxiliary send on your mixing desk to feed the input of the AN-1 then it will not be necessary to include the clean feed of that channel in the mix. In fact, if one introduces the clean feed into the mix, the depth of the comb filters are changed and the effect of the AN-1 is negated. It is possible, therefore, also to take a clean feed to the AN-1 from a tape return or an insert send without routing that particular track into the mix.

In Use

Hours of fun have been had by the Gateway Studio staff when playing with the AN-1, trying it on all sorts of different instruments and vocal combinations. One of the first things we tried to 'spread' into stereo was the output of a Yamaha DX7 going through many of its presets. We were pleased at the amount of variation we could get using the Width control. Using full width on some of the presets, particularly those very rich in harmonics, we were able to create a very wide stereo picture not unlike that which can be obtained from some digital devices costing many thousands of pounds. This wall-to-wall sound (also most effective on headphones) still retains the element of a true stereo perspective.

Of course, one does not always wish to use this huge stereo width and it's possible to bring the picture to a central image by using the Width control.

Engineers have, of course, for many years been simulating stereo by using varying amounts of delay panned anywhere in the sound spectrum against a clean sound and sometimes this delay has been modulated to simulate the effect of comb filters. Any type of delay can be used for this from the sophistication of the harmoniser to the ultimate amplifier and stereo pair of microphones in the bathroom. This is the first time, however, that I have heard a device which gives me the 'feeling' of stereo space.

Switching in the modulation section brings in a low frequency oscillator applied to the delays of the AN-1 and, depending on the amount of Width control used, many interesting vibrato and chorus effects can be obtained. Of course, the rate of the low frequency oscillator can be changed to vary things from slow chorus effect to a fast warble. The amount of Depth control that can be used will vary with the position of the Width control before the onset of 'de-tuning'.

Wonderful effects were obtained on vocals and backing vocals with the Width control in its maximum position. Very interesting effects can also be obtained on some unlikely instruments like the bass guitar, particularly one that has new strings, with all the upper harmonics that their brightness gives. One engineer that I have spoken to also achieved very interesting results by feeding a mono send to the AN-1, sending its stereo output to two monitor speakers and miking these up in stereo and feeding them back into the mix. Probably not what the manufacturers intended but fascinating all the same.

We also took a rather lack-lustre mono mix of a track and fed it to the AN-1 stereo simulator which added a wonderful stereo perspective to the mix. We then tried taking mono sends from an equally boring stereo mix and seeing what the simulator would do to them and found that our resultant mix was much more interesting than the original.

Conclusion

We have lost count of the number of different applications we have tried with the AN-1 and the different combinations of stereo width control and panning.

Although some of the applications were much more successful than others, we have very quickly become aware of the versatility of this apparently simple device. It will soon become a must for many owners of four and eight-track equipment and I can see that at its reasonable price, many of these devices will also be appearing in the racks of 24-track studios.

The applications in post-production have become very apparent in the work we made it do on mono mixes. Used in conjunction with extra EQ and reverb such applications will become more and more exciting. I recommend everyone to head for their nearest dealer and put it through its paces.

The AN-1 Stereo Simulator retails for £507.15 inclusive of VAT. Details from UK importers Turnkey, (Contact Details).