Opto 2A: Tube Optical Compressor Plugin by Antelope Audio

Antelope Audio describes the Opto 2A as a meticulous model of a tube electro-optical compressor. Its attack time is fixed at an average of 10 ms, which keeps the initial transient response consistent across material.

The release is where the character comes from. Roughly half of the release happens in about 60 ms, and the rest recovers gradually over 1 to 15 seconds before the signal returns to full level. Because the release length responds to the source, a sustained, above-threshold signal recovers more slowly than a brief one. This makes the behavior useful for smoothing vocal and bass performances without a rigid, mechanical feel.

The Opto 2A is positioned mainly for vocals and bass. Antelope Audio notes that the compression ratio varies with the input, which suits performances where the level moves a lot from phrase to phrase.

For vocal tracks, the adaptive release helps keep phrases even while leaving natural dynamics in place. For bass parts, the same behavior can control peaks in lines with uneven note levels. Because the plugin is a model of a specific hardware design, it is best judged by ear on the material you are working on.