4 ms·

The 400Hz* spike could be power supply ripple. * https://fcxinc.com/why-the-aviation-industry-operates-on-400-hz-power/ https://fcxinc.com/why-the-aviation-ind

• sidewndr46 3y ago
  You know I didn't think about this at all. But the flight manual mentions multiple power systems in the aircraft and one of them is of course 400 Hz. I wonder if when these recordings were made someone was actually powering up the whole aircraft by running an external APU of some kind?
  • psunavy03 3y ago
    I think the B-58 used an air starter, not an APU.
  • crmd 3y ago
    It could have been recorded in the aircraft (running under its own power or on shore power), or in the shop running off a bench AC power supply. Either way, if the unit's power supply filter capacitors are degraded (which is very likely), then the AC power supply frequency will leak into the audio output. I deal with this nonstop servicing audio amplifiers from the same era as the the B-58.
• duped 3y ago
  It sounds a lot like a whine from an old motor, maybe the one spinning the tape reels. My guess is someone hacked the output to a speaker and stuck a microphone next to it to record, and the hiss/whine comes from the tape machine itself.