Attenuated Vocals on songs

I have been trying to dump all of my old cassettes via Audacity 1.2.6 to multiple external hard drives (Iomega 1.0 TB and 1.5 TB) and I have run into a a number of songs where the vocals have been suppressed so that the background music overrides them.

This happens when I am dumping one side of a tape and one or two songs are degraded while all other songs are perfectly ok. The tapes being affected are Time/Life series which were created in 1988. The tapes are in excellent condition are where created using Dolby B noise reduction systems.

Is this something that can be seen often, perhaps some kind of copy protection? I know that many VHS video recordings have been made with a minimal amplitude sync signal which goes below minimums needed for a VCR to sync when a copy is made.

I have processed six tapes thus far with 9 songs ending up as unusable. I was using two different recorder/reproducer units and they occurred on both. One recorder is a Grace Digital Audio device that incorporates the tape to USB system. This unit has built in speakers so I can monitor the music as it is being played while the other is a simply player that I can listed to using headsets (Koss 4AA Titanium). The affected songs sound great but something is happening during the transfer via USB process. I’m pretty confused here. Any suggestions out there??

Possibly distortion is uncorrected preemphasis of the Dolby B encoding (which boosts higher frequencies).

Playback without noise reduction produces a noticeably brighter sound

Could try deemphasis equalization similar to Dolby B*, (i.e. attenuate frequencies above 1KHz, a.k.a. cut treble),

[* dynamic expansion of higher frequencies would be necessary to properly deemphasize Dolby NR recordings]

Ok, I’ll give the cutting of the treble in equalization a try and see what happens/ Thanks