First, a little background:
In the 1970s and 1980s I recorded some live broadcasts over WGBH FM radio, including Boston Symphony Orchestra live performances, via a good (Yamaha T-1) tuner and a good (Advent 201A) cassette deck (long gone). I recently decided to digitize these so I could get rid of the cassettes and my refurbished Sony K707ES cassette deck. I digitized at 88.2/24, feeding cassette output into a LineStreamer+ A/D, into a Windows 10 Audacity 2.3.3, also set to 88.1/24.
Doing that, I am ending up with a low level high pitched background sound on the recording. It is a simple ‘whistle’ like sound. I used the Audacity 2.3.3 Analyze ‘Spectrum plot’, but nothing stood out. I did see a spurious line at the high-end of the spectrum on 1 recording, and I tried to clean it up using the notch filter set to match the line I was seeing. That did remove that spike, but not the low-level background whistle.
Any suggestions how to determine and remove this sound? The good news is that it is only very slightly audible when music actually plays. I’m guessing that the source of this sound was upstream from Audacity.