isn't larger than the default playback buffer size when
starting Ardour without a previous ~/.config; having
disk_io_chunk_frames larger violates basic design
assumptions and causes phantom underruns in playback
(#4308).
git-svn-id: svn://localhost/ardour2/branches/3.0@10079 d708f5d6-7413-0410-9779-e7cbd77b26cf