low level high pitched background sound on recordings

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.



Sometimes you can drag-select a portion of the show with very low volume or background noise and there will be nothing to cover up the whistle. Also make sure plot spectrum “size” setting is cranked up. A low size setting turns the spectrum display into sloppy mush. But don’t go too high, because a single tone will turn into a graphic needle.

The other thing I would try is capturing a problem tape at the more normal 44100, 16-bit, Stereo and see if the problem goes away or changes. That’s the sound standard for Audio CD.


You can also try [u]Noise Reduction[/u] but listen carefully to the results because there can be side-effects and “the cure can be worse than the disease”, especially when the noise is bad.

…This kind of noise usually gets into the interface’s analog electronics through the USB power. A different computer may have a quieter (or noisier) power supply and/or a different audio interface may be more (or less) immune to power supply noise. Of course, audio interfaces with their own separate power supply don’t have this problem but most USB audio interfaces are USB powered.