Some other bits of jank in the VHS spec:
- Because the tape is moving while it's being written, it stretches the signal out on the tape. This is perfectly fine for normal playback. But when the tape is not moving, the signal's now too wide for the playback head, and you can only read about half the picture. That's why your VCR had bars of static whenever you paused (unless you sprung for the four-head model)
- Audio is still recorded linearly, and you can't exactly chuck a linear head in an angled, spinning drum. So you have to put the audio head further away from the tape. And that distance is fixed; changing it means your machine is now playing audio out of sync with the video.
Also, there is an extension to VHS that lets you record audio along the video in the helical area, it's called VHS Hi-Fi and it improves the audio dramatically with the trade-off that any minor video glitches will add pops to the audio. Humans are way more sensitive to gaps in audio than video, after all.
Yes, those gaps are annoying as all get out. Tracking has to be dialed right in to recover the sound properly.
But, once you do that?
It's really great! Frequency response goes almost to zero, and up to 22Khz, and it's flat for most of that range.
One of the albums I recorded had a warp in it. When the actual vinyl was played on a good stereo system it was possible to see the speaker cones actually move in time with the warp. It's essentially a very low frequency signal.
Cassette does not reproduce that. I bet a good reel-to-reel system would.
Hi-Fi VHS reproduced it pretty much bang on perfect!
The best part was being able to add index marks! While recording, one could press a button and get one of those written to the tape. I had several tapes made with music I really like and could access pretty much anything on it quickly.
Fun stuff!!
The beta machines would phase shift the signal 180˚ every other frame when writing, and they use that for noise cancellation. VHS did four frames at 90˚ each, because of patents.
The read heads were on a spinning drum. Beta machines had an L loading system that would grab the tape and wrap it almost all the way around the drum with the read heads, exposing more tape at once to the reading mechanism. VHS had an M loading system that grabbed the tape on either side and pulled it up, covering maybe half of the drum, because of patents.
And supposedly VHS won out because Sony was begging a lot of money for patent licensing. But tape capacity was probably a factor, too.
Certainly this is how the "applesauce" reader works: https://applesaucefdc.com/
https://www.youtube.com/watch?v=KfuARMCyTvg
I'd recommend pretty much all of his video series to anyone in the HN crowd that's at all interested in analog media formats:
Basically every video he does scratches that itch of learning a new thing about the world. The analog video series is indeed especially fantastic (laserdisc, VHS, B&W vs color TV, blu-ray, etc).
Individual magnetic lines of a VHS tape would only describe half a frame and the two halves would be interlaced back together.
Of course sadly so much content is produced at 1080p24 nowadays for that “film” effect it’s rather meaningless for display purposes.
Online of course it tends to be p50 or more commonly p60 (even in 50hz countries). YouTubeers tend to be able to afford more lights and clearer microphones than big budget productions too.
* 30000/1001
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It's a lot like decoding music from vinyl grooves based on a 2D image scan of the vinyl.
I don't remember the precise terms for the various concepts, but hopefully that shows how specific to a given format the reader needs to be.