Hi there,
Does anyone have some advice that they might be able to share with me regarding how to go about correcting digital audio of both singing and speaking, (The audio was originally on cassette tape, which are amateur recordings, circa 1980’s) I have a mix of audios that need sorting out. Some seem ok, but other audios sound a bit chipmunk like, I suspect the tapes (which, for a long time were stored in a warm house) have deteriorated, somehow stretching the tape or whatever so that the play back output seems quicker, than was originally produced. I notice that Audacity has, in the effects menu, correction tools for Speed, Pitch and Tempo, but which is the 1 to use and how to go about this task?? I really have no idea?
I look forward to hearing back from you
Kind Regards Gin
On the more recent versions of Audacity you can vary the speed as it plays until it sounds right.
see … https ://manual.audacityteam.org/man/play_at_speed_toolbar.html
Then apply that experimentally-derived speed value to change speed
Now the bad news: if it’s tape the speed of the recording & playback may not be constant
then you need deep pockets … https://youtu.be/qqK6wgsh3QA?t=107
There were some dictation machines that recoded at half-speed. Of course, they’d play-back at double speed on a normal cassette player. But that’s not “a bit” chipmunk, it’s full-chipmunk! 
And, there were “Portastudios” that recorded 4-tracks at double-speed.
Otherwise the standard was 1-7/8 inches-per-second.