Memorable German is in mixed choir (8)
I believe the answer is:
historic
'memorable' is the definition.
(I've seen this in another clue)
'german is in mixed choir' is the wordplay.
'german' becomes 'ist' (I can't explain this - if you can you should give a lot more credence to this answer).
'is in' means one lot of letters goes inside another.
'mixed' indicates anagramming the letters.
'choir' is an anagram of 'horic'.
'ist' put within 'horic' is 'HISTORIC'.
Can you help me to learn more?
(Other definitions for historic that I've seen before include "Pertaining to what is important in the past" , "Choir sit (anag.)" , "Momentous, noteworthy" , "sort of present" , "Connecting with old times" .)