Cassette tapes sampled at 22 kHz, 8 bits, mono. My idea was to convert it to the format described at Bruno Viviens site, but it hasn't happened yet.
Before starting to decode the tapes, I had a good look at one of them.
If you compare it to the documented format, it is not so trival to get an objective distinction between a short and a long cycle. What is shown is the last part of the leader (all short cycles), the first bit (highlighted: long-short; a one) and the second bit (short-long; a zero).