API 527 Compressor/Limiter - 500 Series (Discontinued)


90 out of 100. Incorporating 20+ ratings and reviews.

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API 527 Compressor/Limiter - 500 Series

Gearank Recommendation

The API 527 appeared on our recommended list for 500 Series Compressors from May 2017 until December 2020 when it had been out-ranked by other compressors.

Rating Source Highlights

Website Source *Rating Value
Sound On Sound Hugh Robjohns 96/100
Mix Barry Rudolph 95/100
*Displayed values are prior to the Gearank Algorithm's adjustments it makes when evaluating the source.


The API 527 is a VCA-based compressor / limiter that is modeled on API's 225L single channel compressor.

This single channel module features a flexible "feed forward" (NEW) and "feed back" (OLD) gain reduction methods that provide you a choice of using the "old way" or "new way" of compression. The "old way" shows how classic compressors are using the gain control circuit while the "new way" provides a newer VCA type compressor that relies on RMS detectors for the gain control voltage.

This module offers options for achieving uncompressed sounds or hard knee for limiting by using the "SOFT"/"HARD" switch for an "over-easy" type compression. Its attack, threshold and decay settings provide a wide range of control over compression. Using its patented Thrust switch allows frequency dependent side chain control.

This compressor uses both 2510 and 2520 discrete Op-amps that gives it API's signature sound.

The 527 is a great choice to use as a compressor rather than a limiter. It's also a great choice if you are looking for a simple yet versatile compressor for tracking vocals and instruments.


  • Controls: Threshold, Ratio, Attack, Release, Output, Thrust, Knee, Type (Old, New), Link, Meter
  • Input/Output Impedance: 160K Ohm/ 85 Ohm
  • Maximum Input Levels/Output Levels: +26dBu
  • Attack: 1 ms to 25 ms
  • Release: 0.3s to 3s
  • Ratio: 1:1 to 1:Infinity
  • Threshold: +10dBu to -20dBu
  • Power Requirement: +/- 15-18VDC
Although this was previously on our recommended list, there are now more highly rated options available which you can see in our guide to The Best 500 Series Compressors.