When you select the “File Sharing – BitTorrent” overlay from the “Add Overlay” toolbar, two extra metric selectors pop up. The third selector from the left allows you to overlay data for individual artist releases. For example, you can view download activity for a particular album.

Select an artist release, and click the “Add overlay” button to add that release to the time series:

The time series now displays the number of downloads for the Aphex Twin album Selected Ambient Works:

If you want to compare multiple releases, simply add more overlays to the time series: