[clue-tech] Sound problems w/ Jack

[Matt Gushee]

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
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.

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.


I would greatly appreciate any ideas about how to solve this.

-- 
Matt Gushee

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