Make a project that contains the clips that make up your audio track that you want.
Then, to save the audio, use SHARE/EXPORT USING QUICKTIME.
Choose Sound to AIFF.
You will have an AIFF file that can be used in other iMovie Projects, GarageBand, Logic Pro, or played in iTunes. If you want you can use iTunes to convert it to AAC or MP3.
i got a pretty healthy track of a concert riff off my dslr vid, but i'd like to polish up the tones a little bit. The upper tones need some separation; they sound a bit tinny. i was going to try this in garage band (dont have) or amadeus which i do have. and then reattach the track to the vid. thank you.
OK Here is how I would approach this.
1) Create an AIFF file, as I mentioned above.
2) Edit the AIFF file in GarageBand or Amadeus
3) Drag the AIFF file into iTunes.
Note: You could also put the AIFF file in any folder and drag it into iMovie from there, but if you ever move it, your project will get a yellow triangle for missing media. So better to put it into iTunes where you are not tempted to move it around.
4) Open iMovie and open this project. Go to the Music Browser and drag the music track into your project. Drop it on top of the first clip in the project. (Do not drop it in the background of the project, or above or below the first clip. You want the audio track to show as a ribbon attached under the video, not as a solid background.)
5) If you are lucky, it may line up with your video. More likely, you will have to adjust it so it syncs with your video. The easiest way to do this is to leave your regular audio which is attached to the video clips active. Then turn on the waveforms so you see a visual of the wave forms. Now you can drag the new AIFF track to the left or right so that it lines up precisely with the raw DSLR waveforms. In addition to the wave forms, you can use your ears so that it is lined up correctly.
6) After the AIFF track is lined up wtth the video track, you will want to select the video track and open the Inspector to the audio tab. Set the volume to zero. This way, you will not hear the original audio, just the audio from your new track.
Hope that makes sense.
Steve - just a little extra information for you to add to AppleMan's excellent advice.
In order to show more detail in the timeline, it's a good idea to adjust the clip thumbnail slider to the far left position. This will show clip thumbnails of 1/2 (half) a second duration. The slider can be adjusted to show a range of durations up to just one thumbnail per clip (the far right or ALL position). So, for example, at the minimum (half second) position, for a 5 second clip you will see 10 thumbnails.
Doing this expands the timeline, showing greater detail in the audio waveforms and allowing you to line up the audio more easily.
The thumbnail slider is located just below the Projects window. There is also a slider under the Events window that can be used to show more (or less) thumbnails per Event clip.
Drop it on top of the first clip in the project. (Do not drop it in the background of the project, or above or below the first clip. You want the audio track to show as a ribbon attached under the video, not as a solid background.)
It never shows as a ribbon, only as a solid green line. But everything works as you suggested.