Hey everyone, I’m a film sound student diving into analog tape recording. Your collective experience would be incredibly valuable here.
I’ve seen this in countless textbooks: bias + audio drawn as a perfect AM envelope. It made me initially assume the head actually performs modulation (then demodulates on playback). But when I checked the driver circuits (e.g., in a Studer A800), the bias and audio signals are linearly summed before the head. No electronic modulation happens at all.
Still, the magnetic pattern on the tape ends up looking like classic AM. And changing the bias level does affect the final audio amplitude. Could someone explain what’s physically happening in the magnetic domain that creates this AM-like effect—even when the circuit only adds things linearly?
I’ve looked into anhysteretic magnetization and Rossing’s 1981 paper, but I still struggle to map the electrical superposition to the magnetic result.
If there are any recording engineers or physicists here, I would genuinely appreciate a simple explanation. Thanks a lot for reading!!!!!!!