Subject: Re: [LAU] midi capture of external hardware over usb

From: Gabriel M. Beddingfield <gabriel@...> · Date: Sunday, December 20, 2009 - 5:09 am

On Sat, 19 Dec 2009, David Adler wrote:
> Some things I unfortunately don't know:

quoted text> 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?"

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