This is possibly a silly question just out of curiosity.
Bias on magnetic tape recording seems to operate this way as a magnetic material eg demagnetized, demagnetized head laminations, tape is self biased to cutoff [Hellyer].
Yet magnetic tape recording sounds so nice. AC bias effectively shift the operating point to the centre of the H-B characteristic on both positive karts of the X,Y axis and the negative quadrant.
Perhaps a bit like making 2 push pull electron tubes operate in class A (electrons flowing all the time).
Class A operation creates least distortion for small signals and saturation if the larger peaks.
But perhaps the title is a very silly question. We can just bias 2 or even a single ended electron tube or transistor with DC. DC looked as a step function has indinite bandwidth (see Fourier transforms).
Why is AC high frequency bias used on magnetic tape? This is possibly for noise considerations. The noise of a demagnetized tape increase when passed through AC bias. But it should increase even more when passing through DC bias [Hellyer]. Also both quadrants of the H-B magnetization curve are used. Like using a push pull amplifier instead of a single ended one. So maximum output level should be more.
Perhaps DC bias for example by using the head as an output transformer in transistor or electron tube circuits may be investigated in Pleiades experiments. (Attention to any voltage, all safety precision must be strictly followed).
How do signal transformer get away with it? If we look at the magnetising current when a sine wave voltage is applied it looks seriously distorted with crossover distortion. But possibly because exactly the same core carries the magnetic flux to link the secondary there is an exact cancellation and the secondary reproduces in realtime almost at the speed of light a sinewave too.
Do transformers with a bit of DC bias sound better or lower noise?
Reference:
Tape Recorders - Hellyer
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