The API 527A Compressor/Limiter takes its place alongside the family of API VCA-based compressors, including the 225L compressor and the 529, 2500 and 2500+ stereo bus compressors. Anyone familiar with these units will feel immediately at home with the 527A.

Features common to the line include front-panel selectable “feed forward” (NEW) and “feed-back” (OLD) gain reduction methods, provide a choice of “the old way” or “the new way” of compression, for the highest level of flexibility in signal gain control. The “old fashioned way” or feedback method is what most classic compressors use for the gain control circuit. The "new way" of gain reduction is more typical of newer VCA-type compressors that rely on RMS detectors for the gain control voltage.

There is a “SOFT”/“HARD” knee switch for “over-easy” type compression, resulting in a very natural, uncompressed sound or a typical high-knee type that lends itself to a much more severe limiting effect.

The patented THRUST® function can also be turned on and off via the front panel, applying a filter upstream of the RMS detector circuit that preserves that strong bottom end.

Two or more 527A Compressors/Limiters can be connected via a DC link, allowing multiple units to be combined for stereo and multichannel applications.

The output level remains fairly constant regardless of threshold or ratio control, much like the Ceiling “more/less” control on the API 525 Compressor. This allows for live adjustments without any noticeable gain changes at the program level.

The 527A Compressor/Limiter makes use of the 2510 and 2520 discrete operational amplifiers and exhibits the reliability, long life and signature sound that are characteristic of API products.

Characteristics

• Feed-forward or feed-back compression;
• Hard or soft knee compression;
• Patented THRUST® switch for frequency-dependent sidechain control;
• Continuously variable THRESHOLD control, with 31 retention positions;
• Continuously variable RATIO control, with 31 retention positions;
• Continuously variable ATTACK and RELEASE controls, held in 31 positions;
• Continuously variable retained OUT level control, 31 positions;
• Gain reduction of 10 segments/VU meter (GR/Output);
• Overload LED;
• IN switch with soft and hard relay bypass;
• The audio circuit uses the 2510 and 2520 discrete operational amplifiers.

Specifications

• Processor type: API 500 Series Compressor/Limiter;
• Number of channels: 1;
• Controls: Threshold, Ratio, Attack, Release, Output, Thrust, Knee, Type (Old, New), Link, Meter;
• Limit: +10dB to -20dB;
• Ratio: 1:1 to 1:Infinity;
• Frequency response: 20Hz–20kHz;
• Bypass: hard bypass, soft bypass;
• Module slot size: single.