 Production of 16-track machines boomed and the number of studios worldwide using these machines exploded during 1970 and 1971.By the end of 1971, there were at least 21 studios in London using 16-track recorders in conjunction with Dolby Laboratories noise reduction.Artists using Trident at this time also included Genesis and David Bowie as well as Queen who experimented with multitracking extensively most prominently on their albums "Queen II" and "A Night at the Opera".