Aphex Aural Exciter - Type B
In 1975 the Aphex Aural Exciter was unleashed upon an unsuspecting studio, broadcast and film industry. Most engineers and producers found that the device gave increased presence, clarity, and a greater perception of 'loudness' without increasing level.
In those days, it was not possible to buy such a unit but the device had to be rented according to the amount of time it was used on each track. A black sealed box with some knobs on was delivered to the studio and there was no way for inquisitive engineers to prise it open and peer at its insides.
In the past few years there have been one or two similar devices on the market at a cost much less than the original, but now Aphex Systems Limited have introduced their Type B low-cost version of the original Exciter.
The Aphex works on the principle of generating, within its circuits, fourth and fifth harmonics of the input signal which are mixed in with the input signal at the output. It is thought by the psycho-acoustic researchers that these harmonics are the minute cues which our subconscious minds interpret as 'presence' or 'realness'. It is claimed that it is these missing cues that the Aphex Aural Exciter re-creates and adds back to the main signal to change the way in which we perceive what we hear. Other conventional types of processors such as equalisers or reverberation, enhance those parts of the signal that are left when these cues are masked by the recording process. The Aphex Aural Exciter replaces these masked sounds.
Because the harmonics generated are derived from the main signal, they are musically related. The harmonic structure of each sound or instrument, therefore, is strengthened, allowing it to stand out from others. This manifests itself in a perceived increase in clarity or treble boost without giving any measurable increase in level.
The main signal going into the Aphex Aural Exciter passes through unchanged. All the processing is done in an outside loop (called a side-chain) and this processed signal is added in very small amounts to the main signal. See Figure 1.
Before the signal in the side-chain reaches the harmonic generator, it goes through a tuneable high-pass filter which removes any unwanted low frequency information. The level of this signal is then metered by a multi-coloured LED before it goes to the harmonic generator. The generated harmonics are then added in with the original signal, and the mix varied by the Mix control.
The unit supplied for review, is a 2-channel stereo device which, of course, can be used as two monos. It comes in its 19" rack-mounted form and is 1U high. At the rear of the unit are ¼" jack sockets for input and output signals of both left and right sides. There is also a switch for adjusting the operating level of the unit to match equipment being run at +4 dBV or -10 dBV, the operating level which is appropriate to most home recording equipment. (More of this later.) Both input channels are of high impedance (47k Ohms) and the outputs are of low impedance (150 Ohms). This means that there should be no difficulty interfacing the Aphex with other equipment. The instructions supplied with the unit give a comprehensive guide to various ways of patching the device. It is designed to operate at line levels and, therefore, there is no input suitable for microphone level.
The controls of the unit are very simple to understand and operate. On the left is the Drive Control which adjusts the amount of gain into the unit. Next to this there is a flashing tri-colour LED which will show mostly green/yellow with occasional flashes of red on peaks. This would indicate a good input level; if the light was consistently green, this would indicate insufficient level into the unit; too much red would indicate overload and possible distortion.
The next control (called Tune) is the adjustment for the hi-pass filter which, as we have said, will roll off any unwanted low frequency information going to the harmonics generator. The tuning of the filter will alter the amount of input level and this will show on the LED. Therefore, it must be used in conjunction with the Drive Control.
The Mix Control adjusts the amount of effect being mixed in with the input signal. As the manufacturers point out and as we found by experimentation, it is easy initially to mix in too much of the device but the in/out switch allows one to make an instant A/B comparison of input and output (original and treated signals).
The day that the Aphex Exciter arrived would seem, in retrospect, to have an element of great 'good luck' attached to it. We were in the process of recording a jingle and the client wanted it to sound "full, yet empty", "dull, yet exciting" and "sparkling, without the music cutting through the voice-over" - perhaps a job for the Aphex, we thought. As we had hoped, by sharpening up the sound, we were able to satisfy the client.
The following day, we were mixing down some old 8-track tapes of a very good and well-known Country musician. These tapes were recorded live and although the music was exciting, no matter how much we EQ'd the individual tracks, they still seemed to lack life. We tried different patterns with our Lexicon Digital Reverb and although this helped, we still could not get the brightness that we wanted. At this point, we were beginning to lack life!
We decided to put the Aphex across the stereo mix outputs of the mixer and add in some of the effect. As I mentioned earlier, it is very easy to talk oneself into overusing the effect and our initial impressions were that the device was making the sound very harsh. By backing up on the mix control and re-adjusting the filter, we were able to make the track spring to life.
We did notice later on in the mix, that on one particular track, where the music was particularly 'jangly', and not completely in time, the Aphex tended to make the sound again very harsh at whatever setting.
This would have been a good time to have used the device to enhance individual tracks rather than the whole mix. Indeed, we found one track where the banjo was very dull in sound and recorded at quite a low level. As no noise reduction had been used, the track was quite 'hissy' and by EQ'ing the banjo, we of course, were bringing up the hiss level. We found that by rolling some of the hiss out of the track, which of course, made the banjo dull, but then processing it through the Aphex unit, we were able to achieve a balance between brightness and tape hiss. This opens up some interesting areas of thought. For instance, what can we do with some of those dull, noisy cassettes that we want to have duplicated to send to record companies?
On our third day as Aphex-excited engineers, we were recording a piece for synthesisers, acoustic guitars and voices. On the acoustic guitars we were using a blend of natural microphone techniques and direct-injected C-ducer signals. When we used a little of the Aphex on these mixes, again, we were able to experience a pleasant sharpness and brightness of sound. We also used the Aphex on some of the synthesiser tracks and on the vocal track and were very pleased with the results.
We eventually learned to be subtle in our applications of the Exciter and found the results to be much more pleasing.
The Aphex Aural Exciter Model B seems to be a very well constructed, simple to use device which has many interesting applications and areas to explore in studio, cassette duplication room and in sound reinforcement operations. It was pleasing to see that the manufacturers had made the device easily compatible with -10dBV operation which is the level of operating that most people in home recording will be using. At the same time, it is easily switch-able for use at the professional level of +4dBV. There are those, of course, whose mixers have been adjusted for the lower level of operating, who have -10dBV for a reading of 0VU at their group outputs but still have +4 dBV across their insert points.
As with all complex pieces of equipment, it is necessary to read the manual and approach the device with sensitivity. We have shown that if the sound is correct at source, it is preferable to use such a device in its creative rather than corrective capacity.
At a price of around £400, this effect will be within the reach of many small studios but possibly out of the reach of many individual home recording enthusiasts. I hope it will not be long before many home recording engineers start forming themselves into clubs and groups where they can share pools of such equipment as the Aphex Aural Exciter Type B.
The Aphex Type B Aural Exciter is distributed in the UK by Atlantex Music Ltd, (Contact Details).
Review by Dave Ward
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