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API 2500 Stereo Bus Compressor


The API 2500 Stereo Bus Compressor allows adjustment of sonic qualities to alter the punch and tone of the stereo mix. One of the 2500's notable qualities is its use of API's patented THRUST circuit for a chest-hitting, punchy bottom end. The 19-inch, rack-mountable unit boasts a dual-channel design that can be configured for stereo compression or for use as two separate units via a single compression setting.

Another unique feature of the 2500 is its selectable "old" or "new" compression. The old style uses the "feed back" type of compression found in the API 525, while the new style uses a "feed forward" type in which the compressor side chain is fed directly from the unit input. Additionally, the output stage exhibits an auto-makeup gain button that permits the user to vary the threshold or ratio while automatically maintaining a constant output level. Further, the 2500 ensures fidelity with its fully balanced design with two front panel VU meters showing input, output and gain reduction levels.

Incredibly versatile, highly musical

When you choose API, you know you’re getting legendary sonic character. And with the API 2500, you’ve got a range of character to choose from. To start, the 2500 is equipped with API’s patented Thrust circuit before its RMS detector, which delivers punchy, old-school low end. There are also two types of compression onboard the API 2500 — Old and New. The Old style uses the feedback type of compression in which the detector is placed after the VCA (as found on the classic API 525), while the New style uses a feed-forward type for a faster response typical of many popular modern compressors.

The API 2500 is stereo-ready, but sports a variable link between the left and right channels, so you can independently put the channels to work on your mono sources. Whatever way you use it, you’ll appreciate having API’s auto-makeup gain button on the output stage. It lets you vary the API 2500’s threshold or ratio, while automatically maintaining a consistent output level.


Sidechain input for creative ducking

Every dynamics processor has a sidechain circuit that examines the signal and determines how much the VCA will reduce gain — but not every unit provides access to its sidechain. In compressors without a separate sidechain input, your main input signal is, essentially, compressing itself. With compressors that have a separate sidechain input — like the API 2500 — you can introduce a different signal that determines the compression action on the main signal.

An overt illustration of sidechaining is the “pumping” effect that’s popular in EDM production. A control signal — a bass drum, in this example — is plugged into the sidechain input, triggering the detector and causing the main signal — let's say, a synth bass — to "duck" under each bass drum hit. This clears the way for maximum kick drum impact. Another classic use is for auto-ducking music under a voiceover, as in a radio commercial spot. Sidechaining can be used creatively in many ways, limited only by your imagination!

API — the legendary American pro audio company

No American pro audio company is more iconic than API. Launched in 1968 by Saul Walker, Automated Processes Inc. began building quality consoles for broadcast applications. Soon, the company’s products found favor with recording studios, and a string of industry-leading innovations (including the 500 Series module, the first VCA, computerized console automation, and more) followed. API produced the 2520 amplifier, one of the most famous op-amps in the recording industry, and their consoles and products found homes in such iconic studio facilities as the Hit Factory, Record Plant, Ocean Way, Sunset Sound, and many others.

In fact, there are over 700 vintage API consoles around the globe — many of which are still in use. And the company certainly isn’t resting on its laurels; today’s API products give you the same unbeatable combination of utility, innovation, and great sound. 

API 2500 Stereo Compressor Features:

  • Incorporates API’s famous 2520 discrete op-amp
  • Variable threshold between -20 and +10dBu
  • Selectable Ratio, Attack and Release times
  • Patented Thrust circuit before RMS detector
  • Variable link between left and right channels
  • Choice of Old (feedback) or New (feed-forward) compression
  • Soft, Medium, or Hard Knee for gentle to assertive compression
  • Auto or manual gain make up
  • 1/4" balanced sidechain inputs

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