Save track files in new Sound model:

* Consolidate migrations
* Add Sound model. Each sound can belong to a track and contains
  informations about one sound file.

app/controllers/sounds_controller.rb

@@ -0,0 +1,6 @@
+class SoundsController < ApplicationController
+  def show
+    sound = Sound.find params[:id]
+    send_file sound.path, :type => sound.mime_type
+  end
+end

app/controllers/tracks_controller.rb

@@ -8,19 +8,11 @@ class TracksController < ApplicationController
   end
 
   def create
-    @track = Track.new(:name => params[:track][:name])
-    if @track.save_with_file(
-        params[:track][:file],
-        params[:track][:file].content_type
-      )
+    @track = Track.new params[:track]
+    if @track.save
       redirect_to @track
     else
       render :new
     end
   end
-
-  def download
-    track = Track.find params[:id]
-    send_file track.filepath, :type => track.mime_type
-  end
 end