I slowed down my audio by 10% to sync up with video shot at another time. I was wondering what filters to use to best mimic the original sound. It's bassier than normal, and I'm trying out High Pass filter and such. I am using FCP but have access to Soundtrack Pro, if there's a filter in that I need. Anyone know what to use?
It sounds as though you slowed down the sample playback speed for the clip, lowering the pitch in the proccess. 10% slowdown is a significant change, and will undoubtedly sound "off." Unfortunately, no amount of EQ or High-pass filterring will restore the clip to its original pitch, since you've already changed the entire harmonic structure. My advice is to go back to the original recording and try a different tactic.
Try using a different time correction plugin. Look for time compression/expansion plugins that will allow you to change the length of a clip without alterring the pitch. I'm not that familiar with the plugins available for FCP or STP, so I can't reccomend a specific plugin.
The standard audiosuite plugins are comes bundled with ProTools and ProTools LE include a time manipulation plugin that will leave the pitch unaffected. The algorythm used isn't exactly the best out there, though, and excessive stretching will give you noticeable artifacting.
Since even high-end timbase correction tools will eventually introduce artifacting, if the sequence is short enough you may be further ahead simply rebuilding the track. Use the pitch-shifted version as a guide, and book some time for ADR, foley, and effects editing.