There are several methods in play:

1. Folks send BIAB/RB/PTPA project files back and forth. These can be enormous, particularly if there are lots of audio files at play. Probably easiest not to try to do this through upload/download.

2. For quick turn-around of collabs, the best 'product neutral' way of collaborating is to use audio files, preferably loss-less compressed files. Audio files have no dependency on the DAW software being used on either end of the collaboration.

One successful method used in the collabs I mentioned above is to use Monkey's Audio files, which are similar to FLAC, but slightly smaller and the process is entirely without cost - other than upload/download bandwidth. http://www.monkeysaudio.com/

The person that is asynchronously 'adding' to the collaboration uses the sent audio file for cues, play-along, etc., then records their part and saves just their part as it's own Monkey's Audio file back to the person coordinating the project, and that person then integrates it into the overall mix as they see fit.

The reason to use lossless is twofold:

1. The audio quality is not affected by the process.
2. Some report that compression can fiddle with the timing internal to the file.

Other methods items that are critical when doing things this way:

1. The passed audio file must have some type of time reference, handwritten notes, etc. so that when it's used by the recipient, it can be time aligned properly. No 'elimiate silent section' type of stuff that can be common in DAW track render to audio processes. Example of such notes: "Guitar Solo should come in at bar 33, which should be xx:yy:zz in timecode."

2. BPM and/or must be exactly known and likely should not have any variation throughout the song, because it will be very difficult to keep alignment on the receiving end.

This last one can be a sticking point if tempo changes are a feature of the composition, and points back to why sharing the original project files might be a better choice for this particular application.

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