Some may find this of interest.

[Deleted User]

I know this won't be very interesting to the majority of readers, but it might have some value in general terms. It certainly contradicted some things I thought were true about magnetic tape recording, especially it's early history. As Rod Serling used to say, "Submitted for your approval":
https://ethw.org/Some_Popular_Misconceptions_About_Magnetic_Recording_History_and_Theory

[Deleted User]

One of the things I found very personally interesting was number 2, "we think we understand how AC bias works". The reason I say personally was because a long time ago when I just became interested in audio in general and was trying to learn everything I could about it I read somewhere (maybe Audio Magazine) about how tape recorders work. The section on AC bias became my first audio related puzzle to try and understand. During the recording process the sounds you are trying to copy are mixed with a very high modulating frequency (usually four times the upper frequency limit of the tape recorder). So, if at one split second the tone you wish is 440Hz this gets mixed with 80,000Hz and fed to the recording head. This is done to reduce distortion. The 80,000Hz is filtered in the playback and everybody's happy, voila. But I had the hardest time trying to understand how and why this happened or was needed. I'd look at the graphs and the illustrations and sort of figure out how things worked. But it's nice to read that I wasn't alone, lots of people have been trying to figure that one out (20 page explanation!).

mhardy6647

Well, I guess the one thing I "knew" about AC bias was the tendency to get heterodyne products ("birdies") from the bias oscillator and the 19 kHz FM pilot signal
Other than that -- well... I'll read the article. Thanks!