as reported by @sdj on issue #7
update your ffi-coremidi gem to v 0.1.7 and see if this issue is improved.
corrected: update to 0.1.7.
I'm seeing latencies of ~1 second using Mountain Lion and Ruby 1.9.3p327 =/
Odd thing is, I'm seeing shorter latency when using ffi-coremidi directly: https://github.com/arirusso/ffi-coremidi/blob/master/examples/input.rb