Function tape_saturation 

pub fn tape_saturation(x: f64, level: f64) -> f64

Tape magnetic hysteresis saturation.

Models the Jiles-Atherton hysteresis curve simplified to a modified tanh. Tape doesn’t clip sharply — it saturates asymptotically. The saturation “knee” is softer than transistor or op-amp clipping.

level is the input amplitude at which the tape reaches ~90% saturation. Typical values: 0.6-0.8 for different tape formulations.