A:a VOCODER ,I think!!
So why don't try to work on a sw version of the most famous and playable of all old vocoders?the Roland Vocoder Plus VP-330!
Some reasons why to choose this model despite the others:
1.Its sound path is simple and may mean cpu friendly
2.At the times the VP was the first vocoder able to render faithfully the pronounce of consonants with a clever use of a noise generator
3.It has a warm,breathing,uncoomon sound,though its vocode palette is not vaste
4.The voice output can be mixed with the internal pads
5.The strings and human voice presets are smooth ,useful and versatile pads,used at the times from electronic to jazzfusion music,and they're still looked forward by a wide range of musicians
6.It was idiot-proof for its few but well targeted controls
So ,give yourself ten minutes to think about it,you would tie my music budget to you! :wink: