No matter how frequetly _ the works of Beethoven always attract a large number of people.

在英语中有些表示时间,条件,方式或者让步等的从句有时可省略一些成分：如果从句的主语和主句的主语一致（或者从句的主语是it）,而且从句谓语中又包含be,那么这个主语和be动词都可以省略.
When (he was) asked how he gained first place,he suddenly
became cheerful.
If (they are) operated by computer in the future,many of the
trains will have no drivers.
Although (it was) sold by a German company for the first time in 1899,aspirin has been around much longer than that.
They looked around the room as if (they were) looking for
something.
The boys will go out to play football whenever (it is) possible.
你的句子No matter how frequetly (the works are) performed,就属于这种情况