Yamaha CS-15 Video Demo Part 2 

. . : ::DUOPHONY on the Yamaha CS15:: : . .
Forgive me if this is a bit long-winded ;)
Unlike synths akin to the ARP Odyssey, which has a built-in duophonic keyboard- a triggering mechanism capable of sending two different voltages to each individual VCO- the Yamaha CS models only send one voltage to both oscillators internally.
To achieve this 'duophony' on the Yamaha requires a second analog synth (another yamaha or a korg synth- for two reasons), or an external controller: a midi keyboard and a MIDI-to-CV converter box. Essentially, you some second voltage source to control the second oscillator, and if desired, a second gate/trigger to control EG1 (and whatever else it's routed to).
For the additional analog synth option you need a yamaha or korg.
This brand is necessary because:
1) the voltage scale (the yammy and the korg are linear, whereas most other brands, like moog, arp and roland are logarithmic: check this out: en.wikipedia.or... (great article)
2) also on that page is the issue of the gate or trigger.
These two brands are the only two in which both the VCO voltage scale and gate/trigger combination resides.
For the converter box"
It's fairly straight forward- I'd recommend one the Kenton products, personally the Pro2000 MkII. This sends a CV to the VCOs and can send a gate/trigger to EG1. The box itself is very nice and can be configured to send any combination of voltage scales and trigger types- I used this setup a lot when I had my SQ|80's sequencer controlling both my Yamaha and a Roland MC-202 (which I'm thankfully now shot of).
Demo of the Yamaha CS-15 analog synthesizer, part 2 of the video demo.
Overview of the envelope generators, VCAs, oscillator glide, high frequency LFO modulation.
The closing sound is the CS15 with some delay and slight reverb. All of the sound within the demo was made using NO effects, other than a simple three band EQ from my Roland KC-550.