This may be common knowledge (I am certainly no expert), but while documenting and examining the many varied communicator chirps in TOS, I discovered that almost all of them are spliced out of a single 10-chirp sequence. This actually makes a lot of sense. The sound is an only slightly modified recording of an owl chirping, and there is so much variety that I can't imagine they would have relied on multiple recording sessions with a wild animal, especially considering the relatively primitive state of audio editing/processing in 1966.
I found a few sequences that were probably spliced from a different segment of the recording, but almost all of them (at least from the first season) originated in that main sequence. I've identified & confirmed 20 unique patterns so far, all from the same source. The chirps pulled from episodes look a little "fuzzy" - this is from background noise, music, talking, etc. Not only to the timings line up, but they're really obviously the same when listening to these segments side-by-side with their corresponding segment from the 10-chirp.
I was fully expecting to have to scrounge for the cleanest clips I could find throughout the series and do a bunch of splicing on a chirp-by-chirp basis just to get close, but nope! The 10-chirp sequence was made available absolutely clean on the licensed "Star Trek Sound Effects" album, and can be downloaded as "
TOS Chirp 1" from TrekCore. This is going to make it way easier than I expected to build a good sounding and accurate "chirp library" for random playback via microcontroller/DFPlayer in my communicator.