Interesting topic.
I have gone through, and worn out, several cassette decks in my lifetime (so far). Most of them were equipped with Dolby B. Mostly, I recorded my tapes with Dolby B on, and played them back with the Dolby turned off. This made the recordings sound "brighter". In retrospect, I was probably making up for the poor quality of the speakers in my cars.

I never bothered with DBX, except to play back vinyl records. I had, at various times, a DBX 117 and 119. The 119 was more linear, but they otherwise worked very similarly. I used the "expand" function to increase the dynamic range of the playback. At the time, it gave my vinyl albums a "similar" dynamic range to the CDs that had just become so popular.

Backtracking a bit... Something that helped the fidelity of cassettes was the introduction of CrO2 and metal tape coatings. It allowed a much higher level signal to be recorded onto the tape, without saturating the oxide coating. They also needed to be played back with the same setting (I believe it was bias frequency) with which they were recorded, in order to not sound too bright.

The biggest problem that I ever had, personally, with cassettes, is that they were not heat tolerant. If I left my tapes in my car, in the sun, they would tend to "squeal" when played back. (That is, the tape would vibrate or chatter as it moved across the head. At about an 8KHz frequency.) It caused a loud squeal to be reproduced. (If you listened carefully, you could hear the same squeal coming from the tape mechanism itself.) I never found a fix for it, but Maxell UDXL-II tapes seemed to minimize it, while TDK SA tapes were the worst. This only seemed to happen with CrO2 tapes.

[This message has been edited by Raydar (edited 07-17-2022).]