First of all,

do not make the mistake by trying to build a generator for audio-purpose. The quality of such a generator MUST be very good to get some meaningfull results.

Evenso a generator based on a microcontroller seems to be easy, but don't forget the timing! Different software paths must be equal to get a normal signal layout.

To hatem :

Wire the CLK of the counter to a NE555 timer circuit.
The output of the counter must be fitted into the EPROM/FLASH. If you use D7 as a RESET for the counter, you'll be able to implement different patterns into ONE EPROM.

The databus D0..D6 must be wired to the DA. The output can be filtered to get some Analog signal. This is the most easiest way to build a 'random' signal generator.
Output signal selection can be done with the remaining Address-lines of the EPROM. Use a rotary switch and a 8to3 decoder to get a selection for 8 different signals.

By making the CLK (NE555) adjustable, you get a frequency 'random' generator.

The version with a microcontroller can do exactly the same but needs more engineering.

Have fun.

If you put your email-address on this forum, I'd be glad to help you out with your design.