I’ve noticed on some of my older VHS tapes, at the beginning and end of the tape, a faint sound like a telephone being dialed. I don’t hear it on more recent tapes - only ones from the late 80s - early 90s, but maybe that’s just my perception. Is it some sort of time signature thing?
I don’t think I’ve ever heard it on VHS tapes, but I have heard it on audio cassettes and wondered about it. It sounds like some kind of test signal, but why would you need to test your stereo before listening to music?
They are probably test/calibration tones. They are used to check and adjust the equipment used to record and playback the tape. They can also be used to check the performance of a production lot of magnetic tape.
I don’t know the answer. However, my wife and I were watching an old tape last weekend and those tones came on. She asked me about them and I told her I would find out. Good timing.
Some cable channels used to have the “phone tones” as well, especially ESPN. If memory serves me correctly, they were usually played just as the network feed was returning from local commercials.