Analog encryption algorithms
Some people define "encryption" in such a way as to exclude analog techniques -- there is no such thing as "analog encryption", they would say, because any analog method of obscuring the contents of a transmission is, by their definition, "scrambling", not encryption.

There have been several such scrambling ("analog encryption") techniques, including:

voice scrambling:


some early analog secure voice techniques, as you already mentioned, which added noise (or classic symphony music) from a phonograph at one end, and subtracted the "noise" from an identical, synchronized phonograph at the receiver.
Some analog voice scramblers do frequency inversion
Some analog "rolling code" voice scramblers frequently jump to a new frequency, hopefully faster than any eavesdropper can track, similar to frequency-hopping spread spectrum
Various combinations of the above -- for example, the analog A-3 and the 5B machine built to "decrypt" it which "the speech spectrum was being split into 5 bands, inverted and translated ... the cipher controlling the switching repeated cyclically after 36 sections."
I've heard rumors that some early speech scramblers used an analog vocoder to dissect voice (using a bunch of analog bandpass filters and an analog envelope detector for each one) into a few "control signals", each of which was transmitted on its own (very narrow) analog band (each one independently frequency-hopped, and random gibberish transmitted on unused bands?), and then the received control signals were used to reconstruct an approximation to the original voice.


Some analog "television scrambling" techniques:


Some scrambling systems transmit the visible part of each line exactly the same as normal analog video, but mangle the Horizontal Sync so that standard analog TV receivers can't lock on.
Some scrambling systems invert the black-white luminance of some lines, each line inverted/normal according to a bit from some pseudorandom number generator synchronized with the video signal.
Some scrambling systems invert the red-blue chroma of some lines, each line inverted/normal according to a bit from some pseudorandom number generator synchronized with the video signal.
Several scrambling systems use various combinations of the above.
Videocipher I, Leitch Viewguard, VideoCrypt-S, and Nagravision Syster all scramble video by sending the video scan lines in a scrambled order.
Telefirst ("Tele1st") apparently used some sort of analog scrambling technique (?)
Zenith Z-Tac cable scrambling system apparently used some sort of analog scrambling technique (?)
VideoCrypt I, VideoCrypt II, and Eurocrypt use line cut-and-rotate -- each line of the image is cut into 2 parts and swapped; the exact cutpoint is determined by a pseudo-random sequence generated by a smartcard from a seed value.


All of these systems were developed under severe cost constraints, so they sacrificed some security for lower cost to manufacture legitimate receivers.
So for a long time there was something like an arms race between the "defenders" (pay-per-view broadcasters, military radio manufacturers, etc.) and the "attackers" ( pirate decryption, military codebreakers and cryptanalysts, etc.).