How It All Works

Testing testing

Frequency response is absolutely flat in the audio range, THD distortion is at .05% at nominal levels, noise is at -84 dBV. The meters seem to tell the truth just fine, with only slight disagreements with my Loftech when we got into larger amounts of gain reduction - no errors you would notice in normal operation. The low-cut sidechain filter seemed to kick in around 120 Hz. and really reduce the gain reduction below 80 Hz., just like the manual says. The Spectral Phase Refractor™ (SPR) adds increasing phase-shift to low frequencies, so that there seems to be about 90° of phase shift at about 90 Hz., 180° at about 65 Hz. and 270 degrees down around 50 Hz. As far as I could tell, it didn't do anything else.

I have no reasonable way to measure attack and release times, but they sounded pretty reasonable, and the unit behaved very well. Note that at the fastest attack and release times, a hot signal will start to sound grungy. This is not a fault of the compressor, just that it's tracking level fast enough (which is a good capability) to approach audible amplitude modulation. Try compressing pink noise and you'll see what I mean. The High Frequency Expander (HFX) also measures well, doing pretty much exactly what the manual suggested, although in actual use, the maximum expansion sounded like more than 6 dB to my ears.

Audio impressions

I tried the Aphex out on a bunch of different finished recordings, some test signals, basic tracks and barnyard noises. I have two primary impressions. The first is that the unit allows for a great deal of control and precision in manual mode. It is really easy to get the attack and release times sitting just right for a given tempo, so you can let through just enough attack and have just the desired gain reduction for just about any rate of event. For steady, repeating conditions (drum tracks, sequencers, etc.) the manual mode really works well. Selecting "soft-knee" does a lot. The manual says that soft-knee starts the gain reduction slightly below threshold and increases the ratio as the threshold is crossed, smoothly rising to the specified ratio somewhere above threshold. It sure is audibly different than hard-knee, and seems like it would be pretty useful for some applications, particular expressive voices or lead tracks, using a fairly high threshold and low-to-middling ratio. Possibly also for +10 peak limiting.

The second impression I have is that there is more than meets the eye in the "Easyrider®" mode, which at first glance seems to be little more than a La-Z-Boy kind of choice. Because the compressor is looking at the incoming audio signal as criteria for attack, release and ratio settings, the device is actually functioning dynamically, albeit to a limited extent. I wasn't able to suss out the whole algorithm in the available time, but it sounds to me like a fair amount is happening and what's happening is generally good stuff, both in pop music applications and with classical material too. When using Easyrider®, it seems to work best when you very gently tweak the threshold until you get the dynamic and timbral behavior you want. Gut-feel and musical context 'n tempo determine whether to use the fast or slow setting.

The HFX worked really well, especially when substantial gain reduction was occurring. It is possible to easily dial in just the right amount of high-frequency edge or sizzle once compression values were set.

The Spectral Phase Refractor™ "seemed" to change things when I switched it in, but I couldn't hang onto those changes in my mind as time passed. Keep in mind that it is smoothly and incrementally phase-shifting (delaying) low-frequency content, I assume through an all-pass filter, and such phase shift is very hard to hear. However, I can imagine some neat tricks you could do in mixing context, particularly when you link up two 661s in stereo mode. Definitely an extra.