[LAU] Sanity check needed: Fons's Auto Wah on 64-bit system and CPU usage?

Arnold Krille arnold at arnoldarts.de
Thu Jan 14 04:20:57 EST 2010


On Thursday 14 January 2010 02:38:04 Ken Restivo wrote:
> Turns out that on my Core2Duo, JACK RACK running Fons's auto-wah plugin
>  sucks up 6% CPU even if there is no sound going through it.
> 
> I asked Fons about it; he can't duplicate the problem since he doesn't have
>  a 64-bit system. Hell, I can't even duplicate it on my 32-bit system; it's
>  64-bit dependent.
> 
> I looked at the output with Bitmeter at Fons' suggestion, and it seems
>  there are no denormals, inf's, or nans-- just a very small -230dB DC
>  offset in the code (probably to avoid denormals).
> 
> The CPU usage ramps up before any signal is fed into the plugin. It runs
>  normally when there is signal, but then it keeps sucking up CPU
>  afterwards. I'm feeding it from fluidsynth, and bitmeter says that it
>  isn't sending anthing at all during silent moments.
> 
> It doesn't run away to 99% CPU (or 50% on a Core2Duo), like it would if
>  there were a denormal. But still, why is it using up CPU when there's no
>  signal? That seems odd. And why only on my 64-bit machine? FWIW, the
>  64-bit and 32-bit machines I have are even running the same kernel and
>  RT-patch versions (2.6.26.8-rt12).

Here is a shot:

Maybe the 64bit is better at calculation and -230dB are not yet good enough to 
avoid denormals. What if you change that code to add a bit more offset?

Or use it in an ardour session for testing and try the different denormal modes 
of ardour to see if one helps...

Have fun,

Arnold
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