[ddingus]

It can carry frequencies much closer to DC.

The above mentioned FM upgrade to VHS, called HI-Fi VHS I believe, had excellent audio recording capabilities. I used it to archive albums back in the day, and when I play some of the warped ones back today, the speaker cone can be seen moving where it would playing the original vinyl.

[sobriquet9]

But not DC itself. Even if it goes down to 1 Hz, the circuit in question will saturate in a few seconds, or be in saturation when initially turned on and never get to zero as there is no DC feedback.

[ddingus]

Yes, I did not mean to imply otherwise.

The way I have always come to understand this boils down to what modulation actually is. DC is not modulation. Anything above DC can be, or maybe technically is and must be managed or accounted for. Frequency drift might be one example.

DC is basically continuous wave and the signaling, if any is intended, is basically limited to turning the wave on or off, or the wave just being present.

The VCR was basically reproducing very low frequency waves. One could see the cones moving in and out with the rotation of the 33 RPM vinyl.

The only other analog device that did something similar was an old vacuum tube reel to reel running a very high tape speed. And the effect was not as dramatic.

Both of those devices could basically archive a CD respectably. The VCR added about 3db and the reel a bit more that I was not in a position to measure.

The most striking things about that ancient reel to reel device were that it was rack mounted with some other gear, EQ, pre-amp, amp, and some other things, and how much better it could really do when using pretty great tape at crazy speeds. The highs would start to roll off pretty high, 18khz or so. The usual was 10 to 12.

That was a very fun old piece of gear. Left over relic from the 60's available for curious high schoolers to tinker with.