To put it short: SoundCloud is a social network for musicians and professionals in the music business. At least that’s the market the website is aiming for, other users (like me) can also join if they are lucky enough to get an invitation. No other website that I know of gives the user that much control over the music that he is uploading to the SoundCloud website.
It all starts with an upload obviously. Not your usual pick a song and hit a button type of upload though. You do pick a song but can add a wealth of information to the upload including an extensive description, genre, bpm, record label, catalogue number, release data, track number, keywords and even a buy this track link.
Artwork can be added as well and a decision has to be made if the song should be publicly or privately accessible. If the latter is chosen users can be picked from the list of followers and followed or by email. Emails will be send to users with a direct link to the song so that they can access it at the SoundCloud website. Those users have to chose a password for the first time and can use that password to access that song and any other that they are invited to.
