Comparing two Opto Compressors

You would think that a specific compressor type will always behave exactly the same from manufacturer to manufacturer……..but that is rarely the case.

In the case of minimum phase designed hardware the circuit path and components used account for the ‘colour’ of the unit. This is why we might choose a Neve over a SSL….simply because one might sound ‘better’ than the other. ‘Better’ being defined as a signature colour. With minimum phase designs the differences from manufacturer to manufacturer are distinct and quite often we base our buying and processing decisions on this distinction.

With digital designs, and in particular linear phase, this distinction doesn’t exist as the topology and build are governed by the process and not the components and circuit path used. Digital components and software driven processing accounts for a linear process that can be measured and replicated. In other words: the same process is duplicated from manufacturer to manufacturer and the results are always the same.

Nowadays, software manufacturers code all manner of minimum phase designed processors and include tools that can flip a processor from one topology to another – FabFilter’s Pro C2 compressor can emulate a number of different topologies at the click of a mouse.

When it comes to compression most software manufacturers make sure to accommodate for all the major topologies – VCA, Vari-MU, Opto and FET are all represented fully and in some cases a single processor will house all these topologies. BUT, would it be correct to assume that an Opto compressor from one manufacturer should behave exactly the same as an Opto compressor from another manufacturer? After all, it is the topology that is replicated therefore all tests should yield identical results……shouldn’t they?

Let us find out in a real world situation by using two Opto compressors from two different manufacturers. But before we jump into the tutorial let us have a quick look at how an Opto compressor works:

Opto (optical) – Uses a  photocell as a detector and a light bulb to determine the gain reduction. Different light sensor types and illumination sources affect the gain reduction in different ways. The time lag between the photo cell and detector makes for a slow attack and release and this makes this type of compressor perfect for processing vocals, performing gentle automatic gain changes and mastering. The most famous opto compressors are the LA-2A and Avalaon AD2044.

In the tutorial I use a drum beat and run it through the Softube CL1B Compressor and the FabFilter Pro C2 compressor making sure to match the settings on both compressors. I will let you be the judge of the results.

Topics covered in this video are:

  • Understanding the differences in Opto Compressor Designs
  • How and when to use them
  • Various Opto Topologies and behaviour
  • Understanding Gains
  • Ceiling and Headroom
  • Coloured and Transparent Compression
  • Working with Ranges
  • Tips and Tricks