I believe the term "x-class" comes from the fact that these ugens can
produce i-rate, k-rate, or a-rate data without having to have a separate
name (with appropriate beginning letter) for each rate.  This notation
is used elsewhere in the manual for the naming of formal arguments which
can take values at any of the three rates; e.g., the "xamp" and "xcps"
arguments of "oscil".

				David Kirsh

David Boothe wrote:
> 
> ...
> BTW, where does the term "x-class noise generators" come from?
> 
> -David.
>