[clue-tech] Sound problems w/ Jack

[Jim Ockers]

Hi Matt,

I probably can't answer your questions but this is a curious problem.

> Well ...
> 
> I have been itching to plug my (acoustic) guitar into my soundcard and
> try some recording and/or effects. I finally got a pickup for it
> yesterday, and have it plugged in, but not all is well. First of all,
> here's some info on my hardware & software:
> 
>    Sound card: Creative Sound Blaster 16 PCI w/ Ensoniq 1371 chipset
>      Not an outstanding card, but it's fine for everyday use and is
>      supposed to be capable of full duplex and 44100 hz/16 bit.
>    Kernel 2.6.15 (Arch Linux stock kernel)
>    ALSA 1.0.10
>    Jack 0.100.0
> 
> Anyway, what I am currently trying to do is apply some interesting
> effects to my guitar sound using Jack Rack (which is a simple GUI for
> combining LADSPA plugins). But when I turn up the input volumes on the

So I don't know anything about this stuff.  Can you provide the output
of the "listplugins" command?  It supposedly enumerates the LADSPA
plugins on your system.

> mixer, well before I can get any audible guitar sound, I start hearing
> an awful electronic pulse--the exact sound varies according to which
> effects (if any) are enabled in the rack. It may be some kind of
> feedback, though if it is it must be happening inside the computer,
> because the only input is coming from the pickup attached to the guitar
> body, and I am listening with headphones.
> 
> 
> For comparison, here are some other things I've tried:
> 
> Direct recording with
> 
>      $ arecord -f cd -t wav /var/tmp/test.wav
> 
>    Works fine. The recorded guitar sound has good tone and very little
>    noise. The volume is very low, but that's to be expected since I am
>    not using a preamp. Anyway, this appears to demonstrate that there is
>    no problem with my ALSA drivers per se.
> 
> Hydrogen with output to Jack:
> 
>    Works perfectly as usual (I think some of the other Linux audio
>    developers could learn a thing or two from the Hydrogen team).
> 
> Rosegarden with sound via Fluidsynth, outputting to Jack:
> 
>    Something's not quite right here. I had this setup working fine a
>    couple of months ago, but now when I try to play a tune, it just plays
>    the first note ... it seems to be the right frequency and is played
>    with whatever virtual instrument I have selected, but it plays only
>    the first note and holds that indefinitely.

How does it "output" to Jack?  Does it use the LADSPA plugin interface
like /usr/local/lib/ladspa/fluidsynth.so?  Or a unix socket like 
/dev/jack?  Or TCP/IP sockets?  Or an audio cable plugged in a loopback
fasion on your sound card?

> Recording guitar input w/ mhWaveEdit plugged into Jack:
> 
>    Nope. I get an error message saying "This format is not supported by
>    the input driver!" This could be clearer, but presumably "this format"
>    refers to 44100Hz, 16-bit stereo and the input driver is the JACK
>    driver--at least that's how I've configured mhwaveedit. Anyway, I
>    have Jack set to 44100/16, so this is kind of weird.

Can you strace this or ltrace to see what system or library call is
failing?  At what point does it throw that error message? Right when
you start the application? Or right when you configure that plugin
into Jack?  Or as soon as you start feeding audio into your card?

Sorry I'm not more help...

-- 
Jim Ockers, P.Eng. (ockers at ockers.net)
Contact info: please see http://www.ockers.net/
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