This pair of videos, via producertech, take a look at getting started with Rack Extensions in Propellerhead Reason.
The first video, above, is an overview of the Korg Polysix Rack Extension. The movie takes you on a brief tour of the instrument, giving an outline of its controls and synth engine.
Next up is an overview of two of the compressors available in the Reason Rack Extensions range – Audio Damage’s Rough Rider and Softube’s FET Compressor. The video demos how they cope in extreme compression situations, how they differ and their various merits.