[LAU] More jack woes

[Len Ovens]

On Wed, February 13, 2013 5:40 pm, Bob van der Poel wrote:

>> The greatest bugbear of using audacity directly for recording is that it
>> uses
>> portaudio which doesn't create any connections until you actually send
>> it data.
>
> Yeah, I've heard others mention this. Why is it a problem?

Probably means with jack. Part of the reason for using jack is to be able
to change routing and add audio blocks in the middle of the audio signal.
For example:

Sax -> mic->jack->eq->jack->reverb->jack->audacity

So the user starts jack and has the mic sound on capture-1. The user can
hook that up to one of the meter programs to see the signal and set the
the audio card inputs to the right amount below clipping... Or better use
the Audio IFs meters.

Next they try out some eq and decide they want to leave that in. (actually
I normally record dry) so now they have:

Sax->jack->eq->jack->headphones

Anyway they end up with:

Sax -> mic->jack->eq->jack->reverb->jack

And start audacity and try to connect jack to it.... but there is no
audacity ports (actually they would be portaudio ports)... Those ports
don't show up till you hit the record button in audacity... then they show
up, but they are auto connected to the capture channels. The user while
recording (hope they know how to use pause) has to disconnect the
portaudio input ports from the capture ports and reconnect them to the
reverb output ports. Fine now they can record a track.

Having recorded a track (one or two channels as may be) they decide to
record another track. The expectation is that the connections will be the
same... but they aren't. As soon as you stopped recording the portaudio
ports vanish and when you start again they are connected back to the
capture ports instead of what you did before, so the reconnect to reverb
has to be done over again.

The user thinks maybe I can use some session management to do the
connections for me. Only one problem, portaudio renames the ports to a
different name every time it creates them by adding a number as part of
the name.

A good jack aware application opens jack ports as soon as it starts up and
leaves them open for as long as the application remains open unless the
user asks other wise.

-- 
Len Ovens
www.OvenWerks.net