Manual keyframing or Compressor filter?
 

What are the pros and cons of using a compressor filter in FCP to limit audio spikes? I have been keyframing to keep them down for broadcast (between -6and-4db) but it's getting tedious and I just heard about using this filter but I'm sure there is a drawback right?

I would definitely not try to keyframe everything. As you said it's very tedious... and a compressor can help you out a lot.

2- Which version of Final Cut are you using? This is a key piece of information. The older versions kinda suck audio-wise... but you can put the audio into Peak (which is on the FCP CD).
FCP4 is decent.

Ideally:
Add a compressor filter with a soft knee/curve at the top. Typically these filters show you a picture and it will have a curve instead of an angle. They may be called dynamics instead of compressor.
The soft knee sounds better. If you can't hear the difference it doesn't make a big difference though. At gentle amounts of compression it's not a big deal the quality of the compressor you use.

To hear too much compression, push the ratio to 6:1 or higher, push the threshold really far down (i.e. -30dB), and push make-up gain up 20dB or so.

Mess around with all these settings:
Use a gentle ratio like 2:1 ~ 3:1
Threshold something like -12dB
Attack and release something like... around 50ms ish. (This is a really rough figure)
Make-up gain like 2dB
(Sorry these numbers are going to be a little off)

If you want to make the sound really loud while staying broadcast legal, then a higher quality compressor can help you do that... but from your post, it doesn't sound like you'd need one.

A good article on compression:
http://www.dv.com/dv_login.jhtml;jse...questid=180977
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Thanks so much for your well thought response Glenn. I have FCPHD. I guess Peak is around my hard drive somewhere though I havn't used it. I'll try your advice and post back. Thanks.