The spectrum of the noise attached is weird! A peak at 80Hz (almost) and another at 160Hz. Not either UK or US mains.
But even after applying a 200Hz HPF there is still a lot of hiss at about -45dBfs. That's a BAD cassette!
Also attached is scratch test recording using a Sennheiser headset (calm down, only ~20quid and I would not reccy them) Windows recording level was set to 100% and the recording done via a TEKNET USB dongle. The 'silence' is my room at 10am.
I am at a loss atmo to explain the OP's poor results. I can only suggest taking the mics to a different location and with a different PC.
Dave. BLOODY eyes! The peaks are of course 90Hz and 180! Still not power related mind.
But even after applying a 200Hz HPF there is still a lot of hiss at about -45dBfs. That's a BAD cassette!
Also attached is scratch test recording using a Sennheiser headset (calm down, only ~20quid and I would not reccy them) Windows recording level was set to 100% and the recording done via a TEKNET USB dongle. The 'silence' is my room at 10am.
I am at a loss atmo to explain the OP's poor results. I can only suggest taking the mics to a different location and with a different PC.
Dave. BLOODY eyes! The peaks are of course 90Hz and 180! Still not power related mind.