Here's the lowdown on what happens in SoCal. Or at least my experiences of what took place...
1. Do not go to a CHP or Sherrif's station for a visual inspection!! You will be mocked and derided by the fine officers of our state.

Both the officers and deputies I respectfully encountered, somewhat pretended not to know of what I was inquiring about!! It was like divining tea leafs or something to get them to give me the correct info. (Officer/deputy: "Oh, so that is what you're asking about! Why didn't you say so sooner!?!? *smirk smirk!*

) And I was not asking patrol officers but public asisstance officers based at the stations to deal with the citizens of their region.
2. Call 1-800-622-7733 to set up an appiontment with a state referee station. The two closest to me were at El Camino city college (Torrance) and LA Trade Tech (near USC off of the 110 fwy in Los Angeles).
3. When you go to the ref. make sure you have your: registration, citation, & driver's lic. The guys at the ref. station said that the majority of cars who's owners elect to try to pass the decibel test with their aftermarket catbacks FAIL!! So keep that in mind as you weigh your options. Overall it's about a 5-10 minute procedure if all goes well & you're the only car there. They'll also ask you to pop your hood and will visually inspect your engine bay. For example they looked at, and jotted down the CARB numbers off of my intake and header. Luckily I was in compliance with the laws in that regard and I had no worries.
4. Once you've been signed off by the refs. head off to the court that's listed on your citation. Again, when you go to court make sure you have your CDL, original citation, documents from the ref. station (sticker and paperwork), etc. You might be able to send the paperwork in via USPS but I don't have the details on that method. Supposedly Tuesday afternoon are the slowest day of the week at the courthouse. Don't ask me why, but I inquired and was given that info. by a couple baliffs.
Once I went to court I was lucky enough to be spied out by a traffic court judge. He was able to pull my citation number and have it assigned to his courtroom. I was out of there in under an hour. People who were there before me were still waiting in the line for the clerk's window when I left the building.

Also make sure to bring a lot of quarters!!! The judge actually did me a solid and gave me $0.25 to run out and jam into my meter.
The ref. station was free of charge, and the citation was dismissed by the judge ($0.00) so basically I lost no money, but I did take a day off of work to get everything taken care of.