[LAU] midi capture of external hardware over usb

[Gabriel M. Beddingfield]

On Sat, 19 Dec 2009, David Adler wrote:

> Some things I unfortunately don't know:
> Does the realtime remapping introduce timing
> issues apart from a constant offset fore each note?
> How big is the offset?
> Does this depend on the app used?

For a typical jack app (like midixlate), you only have 
latencies for the hardware ports.  (Usually estimated by 
SAMPLES_PER_PERIOD * PERIODS_PER_BUFFER / SAMPLE_RATE, 
e.g. 1024*2/48000 = 42.7 ms.)  I 
think you get 2x that figure if you're doing both input and 
output -- but it might be 1x.

There's no additional latency for the software 
processing.[1] This is the main advertisement for the JACK 
API -- it adds *no* additional latency.[2]

Peace,
Gabriel

[1] That is, unless you have a complicated JACK
     connection graph, or a processor that
     intentionally creates delays.
[2] See http://jackaudio.org/faq "Doesn't use [sic] JACK
     add latency?"