Hi I'd like to create a music catalog online of my music, where people can have a preview of few secs, and then can download them to be available offline but always by the same web page, something as spotify. Many thanks

Something like this makes it great for an audio player. http://www.schillmania.com/projects/soundmanager2/

You'll want to add uploads through something like carrierwave, but you'll need to add a processor to it so that you can create a preview version of the track. I'm not sure how you can trim the audio but that shouldn't be too hard. I imagine there is something like imagemagick for audio that you can use.