MP2 patents?

I am curious what patents Sisvel thinks it owns on MPEG 1 Audio Layer 2 (MP2). After all, it is surprisingly similar to MASCAM, which was publicly documented in "Low bit-rate coding of high-quality audio signals. An introduction to the MASCAM system" by G. Thiele, G. Stoll and M. Link, published in EBU Technical Review, no. 230, pp. 158-181, August 1988. This should be old enough that most patents on MP2 should be expired.