API 527 Review

API''s latest 500 Series module, the 527 compressor ($895), incorporates various features from other VCA-type compressors found in its product line
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The API 527 compressor includes output, threshold, ratio, attack, and release controls, all with detents for easy recall.

API''s latest 500 Series module, the 527 compressor ($895), incorporates various features from other VCA-type compressors found in its product line—most notably the 225L compressor and 2500 stereo bus compressor. Unless you happen to own an API console, you''ll need a compatible rack frame to use the 527, such as API''s 500VPR 10-slot rack or the 6-slot 500-6B Lunchbox.

First designed by API in the late ''60s, 500 Series modules have small 1.5x5.25-inch faceplates, so the 527''s controls are compact yet ergonomic, and they display API''s signature knob shape and color scheme. Continuous controls are output, threshold, ratio, attack, and release, and all have detents for easy recall. A switch determines whether the LED shows output level or gain reduction. The odd thing about the meter is that gain reduction is shown backward; that is, all 10 LEDs are illuminated when there is no reduction happening, and they sequentially turn off to indicate the amount of reduction, from 1.5dB to 23dB. Another switch allows linking the sidechains of multiple units, although a hardware modification is necessary for that.

A Type switch determines whether the VCA functions in feed-back (Old) or feed-forward (New) mode. Simply put, New is generally more transparent while Old yields more of a distinctively compressed sound. Another toggle determines the knee shape (hard or soft). Again, soft is more transparent while hard clamps down on your signal more, providing the sound of heavy compression, even at lower gain-reduction settings. Yet another switch turns on the patented Thrust circuit, which is a filter inserted into the compressor''s sidechain designed to account for the way low-end energy triggers compression more heavily than high-end energy. It''s not a completely unique concept, yet the shape of the 527''s filter accounts for a different sound than that of other compressors with sidechain filtering, which simply reduce the amount of low-end energy in the detection circuit. The 527''s Thrust filter starts around 1kHz, so more of the low-mid components of your signal pass through uncompressed. The remaining features are an overload LED and a hard-bypass switch, which glows when the compression circuit is active.

With only a single 527 for testing, I couldn''t do stereo drum bus tests through the compressor, so I set up a mono drum submix for some parallel compression. Blending the compressed signal back in with my drum mix thickened up the sound considerably, especially with the Thrust engaged. Cymbals and snare settled into a really nice space—overall, the drums went from sounding like a recording to sounding like a record. On kick drum, the 527 was extremely adept at sculpting the transient of the signal. I could achieve a pillowy, cushioned sound by setting the ratio to 8:1, keeping the attack and release in the middle of their range, using the Old type and soft knee, and engaging the Thrust circuit. Backing off the ratio a bit, slowing down the attack, and switching to New/Hard/No Thrust resulted in a much punchier, more forward sound, appropriate for the sound of the song. I had similarly versatile and effective results on the snare.

On bass guitar, the 527 was highly flexible and useful. I generally preferred the Old setting as it thickened the sound while tightening up the low-mids in a really pleasing way. I assume API''s proprietary transformer had something to do with that. Guitars sounded thicker and meatier through the 527, too, with wayward transients kept in check. I also used the 527 quite a bit on vocals, in both the tracking and mix stage. For tracking, I tended to keep it in New mode with a soft knee to help prevent any discernible compression artifacts; in this mode, the 527 was quite transparent. During mixdown, I altered the settings to match the song''s tempo and character, often opting for the more extreme settings. Speaking of which, a quirk of the 527 is that the auto-makeup gain makes your signal seem louder the higher you turn up either your ratio or threshold controls, so as you approach full limiting, your output control often needs to be backed off from unity—the opposite of most compressors.

I''ve come to really love this compressor during the months I''ve been using it. It''s well-built and versatile—transparent enough when I want it to be, but also able to provide a sound of its own when pushed a little bit. Little wonder, as the 527 uses the same 2510 and 2520 discrete op amps and output transformer that have given API''s products their heralded sound for decades. I''m hooked—API''s not getting this one back.

Overall rating (1 through 5): 5