[ardour-users] Ardour2 and LADSPA EQ

[John Rigg]

On Thu, May 03, 2007 at 10:17:11PM +0100, John Rigg wrote:
> Just compiled Ardour 2.0. Looks good so far, but I just noticed
> a problem with LADSPA triple band parametric with shelves. Any
> gain setting on the EQ that is more than a small amount away from zero
> causes some kind of internal feedback in the plugin and the output
> tries to go full scale at some inaudible frequency (not sure if it's
> DC, LF or HF but any of those could be fatal to monitor speakers).
> Luckily I only had headphones plugged in with the volume turned down low.
> Has anyone else tried this plugin?
> 
> The single band parametric works fine BTW. System is Debian Etch amd64.

This is with everything muted except the channel using the plugin,
which has its input disconnected and the outputs sent to
hardware outs 1 & 2 (mono track panned central). It sometimes behaves
correctly for a few seconds then adjusting the gain on any EQ band
triggers the instability, at which point it goes inaudible. At moderate
cut or boost settings it slowly builds, and at large settings the level
indicator shoots up to about 758 dB accompanied by a loud burst of
zipping noises. Then it goes inaudible again (and stays at that
indicated level) until the plugin is bypassed.

While this is happening the DSP indicator stays at its normal level
(between 1 and 2%) and top shows no increase in ardour or jackd's cpu
or memory use.

John