I wanted to generate audio from the X and Y outputs. There are many voltage-controlled-oscillators that would have worked, but the VGA signal generation only used two of the four NAND schmitt gates in the 74HC4093 so I'm forming two VCOs with the remaining two gates.
The circuits use a rotary switch to change the base frequency by selecting the charge capacitor. A 10k linear potentiometer effects the range in frequency shifts created by the control voltage. The output can be square wave or sawtooth selectable by a switch. The square wave goes through a 1/3 voltage divider to bring its volume levels to the same range as the sawtooth.