I think I’ve done something a bit stupid. I upgraded to 2.1.2 from 2.0.2 because I was getting crackling noise on my tracks.
I clicked replace instead of merge and now I can’t see any of my old aup files. Are they gone forever, or is there a way I can find them again? I didn’t back up to my hard drive alas 
I’m using El Capitan 10.11.4
I’ve never been in that situation, but I don’t think replacing the app should delete audio. You did save the project I hope? Have you searched for .aup and .au files?
An Audacity project consists of an aup file and a folder with a lot of au files. The aup file is a text file that tells Audacity how to assemble the short au files.
Once you’ve finished a project, you should export to you favourite audio format. WAV or mp3, fi, as only Audacity can play Audacity projects.
It is possible the update in itself won’t help that problem, but reducing “Audio to buffer” in Recording Preferences will. See this FAQ: http://manual.audacityteam.org/man/faq_playback.html#mac_buffer.
“Replace” (or “Replace all” on older OS X) deletes any files in your existing Audacity folder that are
not in the new installation. For example if you had plug-ins that were not shipped with Audacity, “Replace” would delete them. So if you were keeping AUP files and _data folders in the Audacity folder in /Applications, they are gone I fear. Are you running Time Machine? If so you should have backups of those files and folders.
When merging the Audacity folder, Mac used to offer you “Keep newer” (or “Merge” on older OS X), which did what most people would want - retain any files in your existing Audacity folder that
were not in the new installation, and update files that were in the new installation. This is what our Windows installer of Audacity does.
But now, using the Audacity DMG or ZIP on OS X 10.11.4, so for example dragging the “Audacity” folder to the “Applications” folder inside the DMG, the only option I see is to “Replace” or “Stop” (which simply aborts the merge). If you saw a Merge button, what exactly did you do in order to be offered that choice?
If this is a change in the very latest OS X we’ll have to create some advice about it, and ultimately perhaps consider a proper installer .PKG file for Audacity. And it would help if we set a sensible starting directory for save and export - we have an issue open to address that. In the absence of that, you should change the Audacity save or export directory to somewhere in your own user space such as your Music folder. Don’t save to the Desktop if you are going to save a lot of files, because OS X can slow up with hundreds of files on the Desktop.
What you could do in future is to rename each Audacity installation folder with the Audacity version number, such as “Audacity 2.1.2”. When upgrading, install the “Audacity” folder for the new version then delete the previous installation folder.
Or, in Finder, select the DMG on the left, which shows the DMG contents in the Finder pane on the right. In that pane, double-click the Audacity folder to open it, then select and copy all the individual files and folders. Click Applications on the left of Finder, then on the right, double-click your Audacity folder and paste the files and folders you copied.
Gale
Thanks for your input. I’ve done a fairly comprehensive search for cup and au files and there’s nothing. Most of it doesn’t matter as it’s completed projects and saved in WAV. However, there are some I was working on that do matter… I did save the files in audacity but I hadn’t exported them as I was still working on them.
Gale, I was running Time Machine but of course I’d unplugged the hard drive to use my laptop in the studio and hadn’t re-plugged it between recording and losing the tracks. I couldn’t actually tell you what I did to upgrade… I followed the prompts and hoped for the best! Thanks for your advice on keeping new files… I think the best advice is to remember to back up properly 