[LAD] [ANN] guitarix-0.04.4-1 release

hermann meyer brummer- at web.de
Sat May 23 19:13:18 UTC 2009

Am Samstag, den 23.05.2009, 05:04 -0700 schrieb warjamy at yahoo.com:
> discussion started at LAD about changing the jack server latency from the app called guitarix (like ardour does from its menu JACK -> Latency). Proposed guitarix patch (by me) works nice against jack2 but not against jack1. See below.
> Hermann,
> I quickly ran guitarix in debug mode through gdb. You get a crash at dsp_audio.cpp, line 469. Looks like memory at output[2] and output[3] cannot be accessed. I tried to understand what you attempt to do but this function (mydsp::compute) is way to much for me to understand. It looks like some sort of auto-code ...
> Anyway, output[2] and output[3] are passed in from process() (process callback function). I believe these arrays should correspond to buffers that you receive from jack audio ports 2 and 3. However, at the time we try to change the latency, they are already unregistered because of DSP.setNumOutputs().
> So it looks to me that resetting the jack buffer size on the fly from guitarix badly interacts with how jack1 handled your port deregistration requests. I don't know why it works with jack2. Running guitarix through gdb against jack2, I could see that output[2] and output[3] were still valid memory locations after changing the jack buffer size on the fly. 

This port register/unregister behaviour from jackd/jackd2 brings me a
lot of headage, but on the other hand it's clear that they interact in
different way's, it seems to be a question of time. Can't exactly say
that, but it look to me that jackd2 is a lot faster in handling such a
The port's 2 and 3 used by guitarix for pass the output over a wet/dry
slider to jconv. This way you can mix the output from jconv and guitarix
(to your soundcart or what ever) to your need's.
They are unused when jconv dont run, that meen unregister and fill'd
with sero's.

> This is a bit unfortunate that we get different behaviors when using jack1 or jack2. I hope you'll sort it out, I don't have more time to spend on it. 
> J.
I have run this prob first time when I switch to jackdmp, so I know now
how to handle this. I have a idea and will try it tomorow, let you know
the result. Good point to the ports 2 and 3.
I have the same output from gdb, but line 469 point to outputport_0 so I
dont think on ports 2 and 3.

> PS: by the way, be careful with hardcoded values. On one hand you have gNumOutChans (= 4), on the other you have arrays declared with [4].
That are different variables you talk about, 
float* 	gOutChannel[4]; --> pointers to the jack_port_buffers
int	gNumOutChans;  --> counter for the used output ports


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