Audio file sharing via the Internet currently uses four common transfer methods: cloud, perishable, direct and FTP. Cloud type transfer is when two users share common storage space on a third-party server, often requiring an invitation from the account holder to the downloader. They offer a few gigabytes of storage for free and more space for a monthly fee. Examples include iCloud for Apple users, Google Drive (15 GB free for Gmail accounts) or Dropbox. As free space is limited, the account holder must clean out transferred content regularly.
Perishable sites, such as hightail.com and wetransfer.com, provide a few gigabytes of free space with a web link that expires in a week or two, which can be distributed to multiple recipients without requiring an invitation or log-in. This is handy for distributing rough takes and mixes to a band, which will automatically expire a week later. Direct transfer is particularly useful on deadline projects where two parties are collaborating live via Skype or Instant Messenger. Select SEND FILE in the chat app menu and your file can be transferred just like the text in your conversation.
FTP (file transfer protocol) takes advantage of server space available to folks with hosted websites. My site is hosted on bluehost.com, which gives me unlimited FTP space at no additional cost, so I don't worry about running out of space or expiring links. I'm able to set up an anonymous FTP account for each regular client with separate passwords. Web browsers have limited FTP functionality, so I recommend getting client server software, like FileZilla.
Preparation of the audio files depends on what kind of production is being done to them and the app used by the recipient. A New York producer may wish a Nashville musician to record an overdub without knowing what recording app they use. The most common method is to record a stereo mix of the backing track at the same sample rate and bit depth of the original session and include a guide track showing an example of where and what to play as a separate track. Both the backing track or stem and the demo track would start at the same time code address a few seconds before the downbeat (preferably with a count off bar) and be placed in the same folder. The musicians overdub file(s) should be returned to the producer at the same sample / bit rate as the source file with the same start mark. Make sure that each file is continuous and, if they have punch-ins or edits, the file must be consolidated.
In Pro Tools, select the region of the overdub track from the start point of the backing track file, hold down the Shift key and click the end of the overdub region. Then select Consolidate from the edit menu (Option-Shift-3). All the edits will be combined in one continuous track from the start point. Make certain you have not cut off any notes and used crossfades at the edit points prior to consolidation. If your recording app does not have a consolidation feature, you can bounce the track in solo from the start point to accomplish the same thing. Always label the folder for each set of files with the sample rate and bit depth and never mix multiple formats together in the same folders.
To send a multi-track session to a mixer, just use the same method with all the files consolidated from the same start point. If you have done some volume rides that you wish to be incorporated into the mix, you can use the same 'bounce in solo' technique to embed the volume rides into the audio file. An alternative method is to export the session as an OMF or AAF session, which can permit sessions generated on one platform to be opened on another. Before using the OMF / AAF method, create a couple of test files into OMF or AAF and open the copies to see what data is included and what is deleted. Then send the test file to the mixer to see what he gets before sending the whole album. If you and the mixer share the same platform (e.g. Pro Tools), you could send a complete session file. Session files usually have a significant amount of unnecessary audio data from either out takes or other titles that make them much larger than necessary. To thin out the data in ProTools, do the following:
Use Save As... in the File menu to make an export version of your session.
Remove the clips from all unnecessary tracks and DELETE those tracks from the TRACKS menu.
After crossfading all your edit points, Consolidate all your tracks from the Edit menu (Option-Shift-3).
Select DELETE UNUSED from the playlist menu to remove all unnecessary playlists.
From the clip menu, Select > Unused, then select Clear Selection. You will be given the option to Remove or Delete. Select Remove, otherwise you will delete all unconsolidated files from your other sessions. If you have a 24-track session and have more than 24 clips, identify the unused clips and remove them from the clip list.
Then select Save a Copy In from the File menu and select Items to Copy > Audio Files and click OK.
In the shown example, the original session had six titles with multiple takes and overdubs totaling almost 22 GB. The isolated session file is about 3.5% of the data size of the original session for efficient upload.
With every upload, it's a good idea to send an email to the recipient that contains the specifications and item count of the files, instructions for what needs doing and contact information in case there are questions or compatibility issues. Request a confirmation from the recipient once they download and open the files.