Low cost and easy DRM for audio content - what are the options?

Question

Audio

There is a desire to trade audio content "without intermediaries" - i.e. not through Audible, etc., but by accepting payments on your site and distributing content from there. If everything is more or less clear with payment systems (at least there are a sea of ​​options on hearing, opinions, descriptions of the experience of use), then the question remains with DRM - who can advise a budget and technically simple DRM solution for audio content? Interested in at least marking downloaded MP3s with user data, so that there is no temptation to upload them anywhere;)