API 527 Compressor/Limiter - 500 Series


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

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API 527 Compressor/Limiter - 500 Series

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.


  • 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


A lot of reviewers praise this compressor for its versatility. It works just as well as a vocal compressor. A lot of users have found its New (feed-forward) and Old (feed-back) setting useful for tracking. As mentioned in a review from the ProSound Network, they tested this compressor and preferred using "the OLD setting on acoustic guitars, strings and less aggressive vocals," which uses the VCA’s output to feed the side chain to work like most classic circuits. A few experts used its patented Thrust feature to their advantage when controlling pumped up dynamics. In Hugh Robjohn's Sound on Sound review, he wrote that even on extreme settings, the sound character of this compressor remains clear and crisp.


A few users have mentioned it doesn't really act as a limiter since it doesn't do heavy limiting.


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.

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.