[Jack-Devel] How does --hwmon work?

David Kastrup dak at gnu.org
Thu May 4 11:17:46 CEST 2017

David Kastrup <dak at gnu.org> writes:

> Ralf Mardorf <ralf.mardorf at alice-dsl.net> writes:

>> If you are using hdspmixer you don't need it
> I was not talking about using hdspmixer.

To expound slightly on that: hdspmixer is not integrated into Ardour,
and as opposed to its Windows/MacOSX software counterpart (Totalmix), it
does not offer Midi automation.

I am currently in the process of Frankensteining a Roland FR1b "virtual
accordion" with soft- and hardware Midi expanders, and the Roland only
has a single Midi connector that is either in- or output.  So when the
registration calls for the Roland to be silent, I have to access the
mixer programmatically.

Since I don't want the software to be tied to a particular soundcard, a
more generic interface that _does_ use hardware monitoring/mixing of
some kind internally when available would seem like the best fit.

But it's not clear to me where which stuff is being done and whether,
say, using jack_mix_box for the Roland sound control will magically buy
me "zero-latency" monitoring or not.

It really depends on what --hwmon does and what interfaces of Jack are
involved.  I can find zilch information on that in the documentation of
either software, the manual pages are vague and terribly outdated and
"just read the source code", while being a possible last resort, seems
like I might be missing something here.  And if I am missing it, maybe
it warrants better visibility so that others in a similar situation
might find it easier?

Many ALSA cards have some sort of hardware mixer, and a whole lot of
them are shakier in full-duplex mode and would benefit from a hardware
monitoring solution where applicable.

So I don't think this is an "esoteric uses" only question.

> The question was what effects jackd --hwmon and/or the Ardour
> monitoring option "via Audio Driver" (discovered after the initial
> question was already posed but very likely related) have.
> Also the question was where information about supported cards and the
> used API to Jack were to be found since the manual page describing the
> options represented the status as of 2003 AD.

David Kastrup

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