How to route digital control lines to analog switches to isolate from analog?

[azone2]

I have a mixed-signal layout I need to complete. It has an 8-bit micro feeding about 16 analog switches/multiplexers which controls a bunch of analog (audio) circuitry.
I know from past experience that if I'm not careful with the layout, including the placement of the power and ground planes, I can get some some transients coupled into the audio from the leading and trailing edges of the digital control switching.

Analog switches are not ideal since the control lines aren't isolated from the audio since they're just controlling FET switching. However this is a consumer product and relays, opto-isolators and other alternative are not in discussion.
With that being said I'd like to be as careful as possible with the layout. What is the best way to route the control lines?

1) The (32) 0-5V control lines from the micro needs a return path to digital ground I guess, so ideally I'd place the analog switches somewhere near the micro and partition the analog and digital so they each have their partition of the ground plane. However, I can't really do this as....
2) ...the analog switches are spaced out around the PCB because they need to be local to the analog circuits they're controlling, or else the analog routing would be complete chaos.

What are some general guidelines I can follow to get as clean a layout as possible?

 

[marce]

One GND plane, remember signals only travel in loops so isolate the digital and analogue by careful placement.

 

[azone2]

One GND plane, remember signals only travel in loops so isolate the digital and analogue by careful placement.

Thanks. yes as I mentioned I would partition the sections on a single ground plane if possible but as mentioned the analog switches are sprinkled around the PCB as they must be close to the analog circuits they are controlling. Since control lines will be passing over into the analog section I'm wondering what are some guidelines I can follow in this case.

 

[marce]

Its almost impossible to give any hard and fast rules these days on analogue/digital placement and routing, apart from the information from people like Henry Ott:
http://www.hottconsultants.com/
As every job is different and brings its own set of problems. I do design with single ground plane to designs with segmented and isolated grounds. What you could try doing in your case is running the control lines as pseudo diff pairs! without knowing the circuit well it is hard to second guess the best option. Slugging the digital rise time may help as well, slowing it down with a series res next to driving gate.
Sorry I cant be a much further help

 

[azone2]

Thanks for the response. I have thought about slewing the rise time just enough to minimize any audible click. Fortunately in my case the switching is mostly for source selection type stuff and not continuous or fast gating so if I just minimize any potential audible clicking and get it down 50dB or more below signal level it'll be fine.