Automatic recording bias according to signal strength

It is amazing how low noise noise a virgin demagnetised tape is.


AC bias produces noise.


DC bias even more and it is somehow mid bass pitched. So far tried on cassette at the normal low speed. See previous posts.


The sound quality looks very promising (DC bias).


When the signal is large noise is masked anyway by the signal itself.


What if:


A side chain DC signal is created according to signal strength by the usual methods of rectification, RC filtering of the signal itself like used in compressors.


And applied as DC bias to the recording head.


In such a way that when there is no signal input, bias is zero. And the tape has max quietness.


Then as signal is increasing bias is increasing too bringing the BH operating point to the middle of the positive quadrant transfer curve.


This sounds like an expander or gate but how would it sound like?


Using DC bias it seems much easier applying this idea.


An electron tube directly connected to recording head (with all safety precautions) may cooperate with the recording head and electron tube bias will translate to head bias. See previous post.



A way to reverse DC bias direction can be to first saturate the tape by a permanent field erasing head and then applying a DC recording bias shifting the operating point down.


These are possibly bad engineering ideas...


Anyway AC bias can be used too in perhaps a similar line of thought.