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Aphex Easyrider 106

4-Channel Compressor By David Mellor
Published July 1994

By simplifying the control setup of the Model 106, Aphex have squeezed four channels of compression into a 1U rackmount — making it easier to use without apparently sacrificing functionality. David Mellor's got a ticket to ride...

Assuming that you want to edge your studio further up towards the professional bracket, one of the most important items on your shopping list should be a compressor. Did I say compressor in the singular? Any quality pro studio would have a selection of compressors on offer, from the ubiquitous Drawmer DL221, which finds a home in many studios up and down the land (including mine), to hideously expensive vacuum‑tube compressors that may be noisier and more distorting than solid state designs, but provide that certain something that can't be found elsewhere.

Every compressor has its own personality, and engineers tend to have favourite models that they turn to again and again. The Drawmer DL221 is, in my opinion, a good, everyday, value‑for‑money compressor. It sounds pretty good, has all the controls you need, and falls in the right price bracket. But just because everyone else has one, that doesn't mean that you have to have one too. There are alternatives, and the Aphex Model 106 may just fulfil your requirements perfectly.


What we're faced with in the Aphex Model 106 is a compressor with a reduced control set. The panel space that has been saved by omitting some of the standard functions has been usefully employed by providing an extra pair of channels — yes, this is a four‑channel compressor in 1U of rack space! A pair of these units could compress the entire output of your Fostex R8, Alesis ADAT or Tascam DA‑88, and with the appropriate amount of taste and decency applied, your mixes could sound a whole lot more professional for it. But hang on a minute, I said that some of the controls you would normally find on a compressor are missing. Doesn't this mean that you won't be able to control the compression effect properly? Not really, because although you won't have such precise control as with compressors like the Drawmer DL221, Aphex have distilled the essential functions of a compressor down to a very small set of controls. Where a full‑spec compressor would have five rotary controls and at least one switch per channel (Threshold, Ratio, Attack, Release, Gain, Bypass switch), the Aphex Model 106 has Drive, Output, Fast/slow, and On/off controls — a grand total of only two rotary controls per channel, but, as we shall see, they do the job.

Like any decent compressor, the Model 106 has a gain reduction meter for each channel. A gain reduction meter is vital to see the amount of compression that is taking place from moment to moment, and also to judge how quickly the gain reduction is changing. Also vital is a stereo link switch, and the Model 106 has one per pair of channels, as it should. When compressing stereo signals, it is essential that both channels have an identical amount of gain reduction applied, otherwise a loud signal in one channel would lead to gain reduction in that channel only, and the sound would momentarily swing towards the other side of the stereo image. If you have a compressor by you and you haven't really considered this before, try compressing a stereo signal and listen carefully to the stereo image with the stereo link switched out. You'll soon want to switch it back in again! I should mention for the benefit of power users of compression that the Model 106 doesn't have an external side chain input, so if you want to do fancy de‑essing, you'll have to go back to the old Drawmer DL221. (You may be able to achieve reasonable de‑essing with the 106 by linking channels and using one effectively as the side chain input, but you'll need to know what you're doing, and I can't promise that this unit is ideal for the purpose).

Soft Knee

In order to reduce the number of controls on the 106, Aphex have gone for a form of 'soft knee' compression. In case you thought that soft knee was some kind of ailment acquired from doing too much Cossack dancing, I'll set the record straight with the aid of Figure 1. The graphs show the relationship between the input and output levels of a conventional hard knee compressor, like the Drawmer DL221, a soft knee compressor like the Drawmer LX20, and the Aphex Easyrider system. The knee, as I think you will see, refers to the transition between the uncompressed signal which is below the compressor's threshold, and the compressed signal when the input rises above the threshold level. Below the threshold, if the input rises by 1dB then the output also rises by 1dB. At a 2:1 ratio, when the signal is above the threshold, the input will need to rise by 2dB to make the output level go up 1dB. In a hard knee compressor, there is no stage in between no compression and some compression. It's either compressed or not, and with high compression ratios this transition can be obvious to the trained ear. I would say that hard knee compression is really only entirely suitable when you are using ratios of 10:1 or 20:1 and you want to make the compression effect as obvious as possible, which sometimes is exactly right for the sound you are trying to create. Most of the time, you'll be trying to compress unobtrusively, which is where soft knee compression comes into its own, because now there is no hard and fast transition point — compression eases in gradually as the signal rises further above the threshold.

The Aphex Easyrider method is like soft knee compression, but, rather than the ratio approaching the selected value more closely as the signal level rises, the ratio continues to increase as the signal rises in level. The Model 106's compression ratio starts at an extremely gentle 1.1:1 just above the threshold, and extends up to 5:1 at 20dB of gain reduction, which is the most gain reduction you would ever want to use in normal circumstances. Already this is telling you something about the Aphex Model 106. It isn't as controllable as other, more fully‑featured compressors, since you can't set the ratio, and the ratio only ever goes up to 5:1 at high levels of gain reduction, rather than the 20:1 that you would normally expect. Of course, the trade off is between price, ease of operation, and the two extra channels you get on this unit.

Rather than the conventional ratio and threshold controls one normally expects, this compressor has a Drive control, which combines both of these functions. You can almost consider it a 'more' control: want more compression? Just increase the amount of Drive. Apart from this, the only control you have over the compression effect is the process speed control, which is a button offering a choice of Fast or Slow. The Speed control seems to work on attack and release simultaneously. On other compressors, 'Attack' would set the time it takes for the compressor to react once the signal has risen above the threshold level. 'Release' or 'Decay' would set the time it takes for the amount of gain reduction to return to zero once the signal has dropped back below the threshold. Although for precise work two separate controls are necessary, it's amazing how well you can get along without them. I couldn't achieve the exaggerated compression effect that I often like to use, however, which involves very short release times, but I wouldn't have expected to on this unit. I'd say that if all you're after is some reliable level control and you want to give your fader fingers a rest, use the Slow setting. If you want a vocal to punch through the mix with nice clear consonants, use Fast.

A pair of these units could compress the entire output of your Fostex R8, Alesis ADAT or Tascam DA‑88, and with the appropriate amount of taste and decency applied, your mixes could sound a whole lot more professional for it.

It's worth mentioning one feature in particular of the Aphex Model 106 in some detail — such an important feature that if it were not present I would not consider the 106 to be a serious machine. Which feature am I talking about? The gain reduction meter, of course, since gain reduction is the essence of compression.

The 106's meter consists of a column of 10 LEDs for each channel. I suppose it is moderately sensible that the zero indication is at the top of the column and maximum is at the bottom, but it seems a little odd at first. There are simple rules to bear in mind (but not always to obey!) when setting a compressor: the first is that the more gain reduction LEDs you see illuminated, and the faster the bargraph changes, the stronger the compression effect you're getting. The second rule applies to conventional compressors with separate ratio and threshold controls, and it is that while signal is present (i.e. not during any gaps) there should occasionally be times when there is no gain reduction occurring. If this is not the case, you'll find that the initial transients where the signal rises above the threshold will be distorted. With the Model 106 there will be times when you have to disobey this rule, in order to achieve the maximum 5:1 ratio that the Easyrider method of compression allows. The only way to do this is to increase the drive control, and you may find your transients sounding slightly squashed. Life is full of compromises and this is just another one you will have to consider.

In Conclusion

The sound of a compressor is everything, and an Aphex compressor ought to sound pretty good, considering that this has been one of their main lines of business for a number of years, and also that Aphex are well known for their VCAs (voltage controlled amplifiers). I can confirm that the sound of the 106 is good. You won't be troubled by excessive noise, because noise is kept to a very reasonable level, considering that one of the side effects of compression is always to increase the amount of noise present. Frequency response and distortion are fine, and I didn't detect any specific problems.

I think it is necessary to consider the Model 106 on its merits as it stands, and not on how it could have been if it were mounted in a larger box with more controls, probably at five times the price. What it sets out to do, it does well, and after testing it with several instrumental and vocal sources, and complete stereo mixes too, I can confirm that you will be a lot better off with this unit than without it. You might eventually wish for greater control, and will perhaps save up for another unit with fewer channels but more knobs. But you'll still have the Aphex Model 106 in the rack for general compression duties, controlling those wayward levels and smoothing the path towards that elusive perfect mix.

Pro And Semi‑Pro

These are common terms which nowadays have no relevance to the way you earn your living. Once upon a time, all equipment worked on the basis that a good signal level was around about a volt. 0.775 volts was given the appellation 0dBu, and +4dBu, four decibels above 0.775V, became known as standard operating level. Then some bright spark came along and said "Let's have another operating level for amateurs and people who haven't quite made it in the business yet; a tenth of a volt should be good enough for them" — so we have an alternative operating level of ‑10dBV or 10dB below one volt. The +4dBu level is better, because it means that the musical signals are pushing the electrons in the wires back and forth to a much greater degree than they would tend to vibrate of their own accord, and so the signal‑to‑noise ratio can be better (sensitivity to interference is also reduced).

Unfortunately, these two operating levels exist side by side and it is now virtually impossible to build up a system where all equipment is designed for the same operating level. Fortunately, Aphex have provided a switch on each channel to set the operating level to +4dBu or ‑10dBV. Consult the manual for your mixing console and set the appropriate level for best results. If you have the wrong setting, the result won't be disastrous, but you may find the range of the controls insufficient, or you may run close to clipping.



  • Servo balanced
  • Balanced 15kΩ (‑10dBV mode)
  • 66kΩ (+4dBu mode)
  • Unbalanced 7.5kΩ (‑10dBV mode)
  • 33kΩ (+4dBu mode)
  • Nominal operating level +4dBu switchable to ‑10dBV
  • Maximum input level +29dBu (+4dBu mode, minimum Drive)
  • +14dBu (‑10dBV mode, minimum Drive)


  • Pseudo balanced, transformerless
  • Balanced 56Ω
  • Unbalanced 132Ω
  • Maximum output level +22dBu (+4dBu mode)
  • +10dBu (‑10dBV mode)
  • THD below threshold 0.005%
  • THD fast process 1kHz 0.06%
  • THD slow process 1kHz 0.02%
  • Hum & noise +4dBu ‑75dBu (Drive & Output at 12 o'clock)
  • Hum & noise ‑10dBV ‑86dBV (Drive & Output at 12 o'clock)
  • Crosstalk 20kHz ‑76dBu worst case
  • Frequency response 3Hz to 54kHz (+0, ‑3dB)


  • Easy to operate.
  • Four channels of compression in 1U of rack space.
  • Switchable for pro and semi pro levels.
  • Sounds good.


  • It does what it sets out to do very well so none, except — yet another external power supply.


The Model 106 is well thought out, compact, especially for a four‑channel device, and capable of a very nice sound. A good choice as a first or supplementary compressor.