When I worked in CBS's tape facility we used a 500Hz tone to set levels every morning on our tape duplicators. As a newby I had to run each tape through a computer dedicated for reading levels and EQ. Daily for over a year I listened, tested and set levels on 150 cassette and 20 8-Track duplicators.

I also performed EQ on our QA and A/B test rooms weekly. I would know a 500Hz tone. I would also know 1KHz, 2KHz, 6.3KHz, 10KHz, 12KHz and 16KHz (standard test frequencies on TEAC test tapes).

Our A/B test engineer had a better ear than I. I was the tech responsible for her hardware. Once she said her 500Hz level test tape was distorted. I couldn't hear it, but when tested it had 2% distortion. Normal spec was +/- .5%.

Most of us listen for pleasure. From my experience those who listen more critically, don't enjoy the music as much. With tape it was very difficult, there's so much that can go wrong bias distortion, scrape flutter, sibilance, wow. Knowing what to listen for at times spoiled the music for me. My condolences to reviewers who's job it is to find fault in different designs. They're always comparing to a reference and finding differences. In the case of tapes, ignorance is bliss.