Overview

The Aphex 661 is a neat 1-rack-unit mono compressor with a couple of interesting wrinkles. I've had chance now to run it through its paces and use it on a variety of recordings. To cut to the chase, it works really well and merits your serious consideration. At $749, it isn't cheap but offers a substantial variety of features and capabilities that go well beyond the feature set found in most cheaper units.

Features

The Tube

A central feature of the 661 is its use of a vacuum tube. Without a schematic, I don't know quite how they use it - the manual suggests they've dropped the voltage supply usually required for tubes and done some other things to integrate it into an otherwise solid state design.

Whatever. It all sounds fine, although, frankly, I couldn't hear any "tube-like" quality, nor did I measure any badnesses pertaining to the tube. Noise, frequency response and transient response all were excellent. Distortion was also very good, although with more second harmonic than usual (ca. 65 dB down or .05%). Maybe that second harmonic presence is what leads to the "tube" sound. Intuitively, such "even-order" harmonics should make the sound a little fuller, but there really isn't much of it. In any case, the Aphex is a fine compressor and has a pretty fair bag o' tricks. Let's look at what it'll do.

The Front

First, there are the standard input level, output level and threshold level pots, plus a bypass switch (hardwired, with a default to bypass if power is lost or turned off - thank you Aphex!). Next, a weird little circuit you can switch in called (I'm not making this up) a Spectral Phase Refractor™ that, according to the manual, "corrects time smear - adding clarity and depth." Man, I love these things!

Getting further into it, the unit allows two different modes of operation. To use the first mode, called "Easyrider®," you select "Auto" and the compressor selects attack 'n release times 'n ratio, based on both the threshold and a short-term history of the audio signal passing through the unit. You can further select "Fast" or "Slow" Easyrider® to change the response speed of the algorithm.

In manual control mode, you get two choices of "knees" (Hard and Soft), plus a good range of ratio, attack and release times.

In the side chain (which is accessible for external processing), a high-pass filter (cutting off below 80 Hz.) is available to minimize LF pumping effects. Handy.

A really nice extra feature is a cool little dynamic equalizer/expander that works only on compressed high-frequencies (got that?). It is an upward expander that adds back high-frequency stuff that the compressor gain reduced It doesn't work when the signal is below the threshold. What a fine idea!

What else? A switched input/output level meter and a gain reduction meter. More switching to permit the compressor to be linked to another compressor and either function as a slave to that unit or in stereo. This is a handy and welcome, if subtle, distinction. It resolves the question of exactly whose sidechain is the VCA going to respond to, anyway? In slave mode, the Aphex ignores its own control signal and responds to the patched link. In stereo mode, the two control signals are summed and that common signal is sent to both compressors. Nice. Solves a bunch of tweaky and annoying little control problems.

The Back

On the back the gzintas and gzoutas are available in both XLR and 1/4" TRS (tip-ring-sleeve) format. Further, the buffer amps are set up so that when you unbalance the signal there is no 6 dB loss. Thanks! Also, thanks for a +4 dBu/-10 dBV switch. You can patch the sucker into and out of most anything, with a minimum of hassle.

Sidechain and link patching is via unbalanced 1/4" phone plugs. Sidechain level is at -10 dbV. Also, it's buffered, so you don't lose audio if your sidechain patch should short out.

All very pro, very serviceable, very user-friendly. Nice-nice. Thanks, Aphex!