Research into sound tracks

I must have a soundtrack or soundtracks in my teaser trailer because music is a big part. Music can add to the atmosphere and the tension. Any soundtracks I use must be from copyright free services. I have looked through many different soundtracks on the website http://www.freeplaymusic.com/ and tried many different sounds to see which one fitted the video the best. I decided that I didn't want just one soundtrack I thought that a variety would have more of an effect. 

     Listening to other soundtracks on trailers, obviously most of them use songs that are well known, or in the charts or suited for the film etc, but I noticed that the pace and type of song had to change so the audience can really feel the atmosphere. I decided that the way to do this was to use a different soundtrack for either the character or the situation. Since I added the soundtracks to my trailer it has made a big difference and I am happy with the final effect. I also used the website http://www.freesound.org/ to get the digital sound at the end of our trailer.