They can make their way into the public's hands in a couple of different ways:
1) The multi-track recordings are deliberately released by an artist who wants to encourage others to remix their music. Sometimes it's just the instrumental. Sometimes it's only the acapella vocals, and other times they release the entire multi-track, or a simplified version of it.
2) There are certain audio tricks that can be applied to separate certain components from a recording like isolating the L or R channels. If you have an instrumental recording, you can use phase cancellation to nullify the instrumental against the full recording end up with just the lead vocals. This technique has it's limitations and isn't always perfect.
3) Box sets for popular albums sometimes deliberately include isolated tracks. The Beach Boys' 'Pet Sounds' box set is a noteworthy in this way.
4) Audio engineers and producers with access to a famous song session or tape reel will copy and leak the entire multi-track recording. This is usually illegal. Nonetheless these are highly sought-after by audio engineers and producers who trade them amongst themselves for their insights into the recording process that they offer.
1) The multi-track recordings are deliberately released by an artist who wants to encourage others to remix their music. Sometimes it's just the instrumental. Sometimes it's only the acapella vocals, and other times they release the entire multi-track, or a simplified version of it.
2) There are certain audio tricks that can be applied to separate certain components from a recording like isolating the L or R channels. If you have an instrumental recording, you can use phase cancellation to nullify the instrumental against the full recording end up with just the lead vocals. This technique has it's limitations and isn't always perfect.
3) Box sets for popular albums sometimes deliberately include isolated tracks. The Beach Boys' 'Pet Sounds' box set is a noteworthy in this way.
4) Audio engineers and producers with access to a famous song session or tape reel will copy and leak the entire multi-track recording. This is usually illegal. Nonetheless these are highly sought-after by audio engineers and producers who trade them amongst themselves for their insights into the recording process that they offer.