The X201 Vocoder was modeled after an ultra rare, ultra pricey (even at the time of its release), Vocoder unit, whose intelligibility has never been surpassed.
Vocoders have created a magical sound for artists like Kraftwerk, Herbie Hancock, Frank Farian (Boney M, Milli Vanilli etc.), Cylon Robots or the unmistakeable voices for the Droids in Battlestar Galactica droids in Star Wars and… Daft Punk (RAM).
The X201 features two Filter Banks, each with 20 different frequency bands to work with. Each Filter Bank can process the incoming signal (usually a voice, but any other signal, including drums, can be processed), or one can use only the internal CARRIER signal. Other vocoders used at the time such as the Roland VP-330 only had 10 frequency bands, it had a very musical sound, but because of the reduced number of frequency bands, it had much less clarity than the X201 does.
You can also use the internal analog Synthesizer as a carrier to input into the vocoder, which immediately gives the X201 its characteristic and recognisable sound. Any other incoming signal at hand can also be used, like an external Synthesizer or another voice etc to drive the vocoder.
The X201 has an exclusive feature called 'Silence Bridging'. It is a Multiband frequency dependent Envelope Follower engine, which will shapes the signal gain according to it's harmonic content. It's very useful for processing percussive or rhythmic sonic material, the Envelope Follower will add consederable contour to the sound.
Usually you input a voice, you do not have to even sing. Then you use the internal synth as the Carrier. You send Midi notes to the Carrier to make your voice 'sing' those notes being played (or chords, because the engine is polyphonic). Et voilà you are vocoding.
There is more. The X201 is full of additional parameters that were not included in the original hardware unit. This makes it much more versatile, and powerful.
XILS also added some vintage analog effects emulations: Chorus, Phaser, Delay and an early ‘digital' reverb unit are all in there. You can also configure and design custom effect routings and different effect chains as well.
Or use the X201 just as a Multi-FX on its own. Use it as a simple Filter Bank/Chorus/Phaser/Delay/Reverb Multi-Effect. Try it on another instrument such as a Rhodes, Clavinet or String Machine patch, and rediscover these vintage organic sounds that require long chains of vintage effects to sound as authentic as possible.