Captured on a rather slow computer back in 2004. The method itself did not use more than about 5% CPU.

AJ Sporka, SH Kurniawan, P Slavík: Whistling User Interface (U3I). 8th ERCIM International Workshop "User Interfaces For All", LCNS 3196, pp. 472 -- 478, Springer-Verlag Berlin Heidelberg, Vienna, June 2004.