Ferro-chromium (FeCr or Type III) Compact Cassettes were produced between the mid-1970s and early 1980s, and were an attempt to combine the best aspects of the previous Type I and Type II cassettes. Ferro-chromium tapes combined a layer of ferric oxide with a layer of chromium dioxide superimposed on top, offering the high frequency definition of chrome tape along with the fuller bass of standard ferric tape.
Sony first demonstrated ferro-chrome cassettes as early as 1973, and invited other manufacturers to adopt their ferro-chrome formulation. Other manufacturers that produced ferro-chrome tapes included BASF, Scotch and Philips.
The bias of Type III was somewhere between Type I and Type II, but tape player manufacturers now had to chose whether to add a new setting for ferro-chrome and although some did, it was not commonly adopted. When Type IV metal tape arrived in 1979, it offered a bigger improvement over Type I and II cassettes and tape recorder manufacturers were more willing to offer a metal tape setting on high-end machines.
It appears that there was never an attempt to add identification notches to ferro-chrome tape when these were introduced in 1979, so ferro-chrome cassettes retained the same notches as standard ferric tape.
Sources / Resources
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