Stem Mastering is when you send me two separate audio files of your music, which allows me to run your tracks individually through an SSL Sigma Mixing desk, giving your intruments more separation & clarity that only manifests when using real analogue summing. This addon is suited: - if you're not sure your mix is 100%, and you want me to get up to 2 audio parts like your Percussion and Instrumental, or Music and Vocals sounding awesome and sitting perfectly in balance with each other just like the top songs of the genre your aming for. - if you're not happy with the tone of your intruments, or there are sounds in there that you dont want, like harshness or boominess, and need me to treat. - if you just want the magic of the SSL Sigma Mixing Desk. 2 Track Stem Mastering is perfect for when you want that extra separation and clarity between your percussion and intruments. For example, in your production, you can't quite get the percussion to have "that impact" that your after. Another example of 2 Track Stem Mastering is processing an intrumental track, and a vocal track. Producing perfect vocals that sit in your music is often the most important and dificult thing to achieve.