*Product: API 2500 Bus Compressor Plug-In
*Developers: Universal Audio
*Formats: AAX/AU/RTAS/VST for UAD2 Systems or Apollo Interfaces
*Price: $299 MSRP
*Demo: Fully-functional for 14 days

The scope: After successfully developing plug-in versions of many sought-after hardware compressors, many of us considered that it was only a matter of time until Universal Audio takes the API 2500 Bus Compressor to the UAD-2 and Apollo platforms. Since their release of the API 500 series EQ Collection a few years ago, followed by the UAD API Vision Channel Strip, it was widely expected that the 2500 would come at some point and it has finally happened. Spoilers: it does not disappoint, which should come as no surprise given UA’s track record on the matter! Once again they had the hardware thoroughly analyzed and deployed their famous point-to-point modelling techniques, emulating everything inside the legendary box, including all the transformers and op-amps that makes for a huge part of the trademark API sound. On top of it UA has also introduced two parameters not present in the original hardware to make the plug-in not only an emulation, but a very special version of this highly coveted VCA compressor.

In use: The API 2500 Bus Compressor Plug-In is relatively straightforward to use, with the usual threshold/ratio/attack/release parameters common on other compressors, featuring stepped controls on the attack, release (when set to fixed), ratio and left/right link amount. This is all well-known territory so that once those basic parameters are set it’s time to check the exclusive tricks that the 2500 offers, which are mostly grouped under the “Tone” tile at the center the interface. Here we have API’s patented “Thrust” circuit, which acts on the detector by adding a specialized high-pass filter in the sidechain path to tweak how the compressor responds to each frequency area - the graphs below should provide some good insight. “Thrust” helps on lot on preventing pumping on material that’s heavy on low-frequency content, which is the case with many of today’s popular music genres, and adds a lot of versatility to this compressor - despite not being as comprehensive as current plug-ins in terms of offering a ton of possible tweaks, “Thrust” is a very effective control and delivers great results without requiring a lot of time. Next to tone are three options for the knee (soft/med/hard) and the two tone type options, which switches from a feedback (“old”) to a feedforward (“new”) topology, significantly altering the character of this compressor. Keep in mind that using the feedback options put the output back in the detector path, so if you increase the output gain there will be more compression, which perhaps is what you want since the lovely API tone comes out even more prominently. On feedforward/new mode the signal that feeds the control circuit is tapped before it’s actually compressed, for cleaner and more precise results, while on the feedback/old mode the control circuit gets the signal after the compression, leading to more tone and color. Another trick worth mentioning is the L/R link amount and respective filters. The L/R link control determines if the compression happens independently on left and right channels (IND position) or if both left/right channels are compressed by the a variable amount from 50 to 100% (full stereo link). There are three filter shapes options (highpass, lowpass and bandpass) to prevent a certain frequency region on left or right to trigger the compressor on the opposite side, which is a good both for maintaining the stereo imaging intact or also to slightly alter for a more pronounced stereo effect. It’s important to note that the filters only operates on stereo mode and have no effect if the plug-in is used on a mono channel.

Sound quality: Excellent sound quality through and through, this is definitely an amazing compressor and will handle your bus duties very elegantly. This is quite a versatile compressor that can do both “stealthy” and “in your face” compression beautifully, but one thing that I really like about this plug-in is how it keeps up under extreme circumstances such as high gain reduction and fast attack/release settings, which can be great to reanimate a group of percussive instruments. Compressors often sound hazy and lose definition when pushed too far, but that’s not the case here, the plug-in manages to retain a good part of the envelope’s definition even when abused, which is quite remarkable. It also works really well for that 1-2 dB knock on a buss for glueing things together, but also adding some extra weight and depth to the sound - I think the fact that Universal Audio has modelled the entire signal path with all the electronics has something to do with this. This was quite evident to me when I compared this plug-in to the other emulation of the API 2500, which despite doing a great job on the compressor action does not deliver this “something else” that the UAD version brings to the table. I also enjoyed it a lot as track compressor, since there are mono versions I decided to give it a go on individual channels and it elegantly handles basically anything you throw at it.

Ease of use: Pretty easy to use once you’re acquainted with the controls and with how the compressor reacts. The interface is great, quite big in fact which is good, all controls are readily available, no hidden menus or extra windows so using this plug-in is quite a straightforward process that shouldn’t present any difficulties. I really enjoyed the VU meters, they provide very useful feedback and can be switched to display input, output or gain reduction, all with excellent resolution and very accurate needle action - it’s one of the smoothest meter I’ve seen in this particular aspect. The documentation provided is also of good quality, covering all parameters with sufficient detail over 12 pages of the UA Plug-Ins (.pdf) document. Perhaps the only downside when it comes to ease of use is that it’s not exactly a lightweight plug-in and will require roughly a quarter of a SHARC chip.

Features: Literally nothing to complain here, quite the contrary! UA not only brought all the features from the hardware but they also included two extra controls which are quite cool and I’d even say they’re very decisive. The “mix” (also known as dry/wet) control is very useful, kind of a must-have these days in the sense that people will likely ask for it if it’s not there, so it was wise to include it. The “headroom” knob is far less expected, so it’s a very welcome surprise to have it here as this is a very effective control that allows for greater operational precision and it also enables cool sonic possibilities, both on the transparent side (more headroom) and on the distortion/saturation side (less headroom). Combined these are very handy controls to have and they take a design that’s already very capable to the next level.

Bang for buck: At $299 the investment required is steeper than the average compressor plug-in, not to mention the previous hardware investment, but there’s really nothing average about this one, far from it. It’s the very top of the heap and definitely one of the best software compressors ever made.

Recommended for: Mixing and mastering engineers looking for a versatile compressor that will deliver excellent sounding results under many different circumstances. Fans of the hardware will definitely want to try this one, it’s definitely the best emulation of the API 2500 to date.