When learning to mix, as with any skill, practice makes perfect. However, the problem many students and teachers face is that there is a shortage of suitable multitrack material available – type 'multitrack downloads' into Google and much of the stuff you'll turn up will be preprocessed stems or incomplete 'remix packs'. Even where raw multitracks are provided, they're often in a low-quality data-compressed audio format, so they don't respond properly to typical mix processing, or just take ages to download.
In response to this, SOS contributor Mike Senior has created an online download library of more than 50 unprocessed multitrack projects, all of which are free to use for educational purposes. Each project is provided as a simple ZIP archive containing WAV files at 24-bit/44.1kHz resolution, which can easily be imported into practically any DAW system. In addition to the full-length versions, most of the projects are also provided in a shorter excerpted form (usually comprising just the production's final chorus), catering for those with slower internet connections, as well as providing 'bite-sized' assignments for classroom use.
A wide range of musical styles are represented, from Acoustic Folk to Electronica to Death Metal, and MP3 previews alongside each listing allow you to quickly browse through until you find something that appeals to you. Because most of the projects are typical small-studio productions, there are plenty of real-world mixing challenges to be grappled with. Indeed, more than 20 of the projects have been sourced from Mike's own 'Mix Rescue' remixes, so if you need some pointers you can just refer to the relevant article in the SOS back issues archive – there's an article link right by the listing.
The library is continuing to grow, with several new projects being added every month. If you would like to help out with the resource by donating some of your own multitrack projects, then just get in touch with Mike through the site.