Part 1 "The Audio Prism Story," by Glen Clark: http://www.thebdr.net/articles/audio/pr ... oPrism.pdf
Part 2 "The Era of Multiband Processing," by Jim Somich with Barry Mishkind: http://www.thebdr.net/articles/audio/pr ... -hist2.pdf
Part 3 "Digital Processing Starts Making Noise," by Jim Somich with Barry Mishkind: http://www.thebdr.net/articles/audio/pr ... -hist3.pdf
Part 4 "WCRB and the Classical Music Wars," by Grady Moates http://www.thebdr.net/articles/audio/pr ... lAudio.pdf
I found some interesting quotes in these articles
You see, there is a lot more magic in the Audio Prism than Glen talked about in his article last month. His control voltage side-chain is a work of art: there are four comparator “trip points,” creating five operational “level windows” for
the audio: [1] too low to do anything with, so do not do anything 'cause it is probably noise, [2] high enough to probably be useful program material, but not high enough to be competitive, so bring it up, [3] right where it needs to be, [4] too high, so bring it down, and [5] way too high, grab it quickly and YANK it down – but release it quickly when the momentary overload has passed. Most other processors of the day only had [2] and [4] worked out, so Glen‟s side-chain was already perfect for classical music.
Another magical thing about the Audio Prism is the musical way that attack and release times were controlled. Up until the Audio Prism, time constants were quite variable, because they were usually derived directly from the peak level of the audio envelope. Glen‟s approach was different – all of the bands in an Audio Prism used the same attack and release time constants. Also the timing was developed with current sources/sinks driving capacitors, for a very smooth, musical gain change.