[LAU] Crackling in ZynAddSubFX

Peter Lutz peter at gotsomeideas.com
Fri Jun 20 22:36:41 EDT 2008

After a little more experimenting, I found a little workaround for this
issue... although it's still doesn't exactly shed any light on what's
causing the problem. I figure I'll post it here to this mailing list, in
case someone with more experience might know what's going on here.

I noticed that every time I switched to a different instrument in the
ZynAddSubFX instrument bank, I would get an Xrun in JACK. Then I'd start
hearing the crackling sound. The crackling didn't show up at first, only
until I switched instruments. I found that if I disconnected ZynAddSubFX
from system in the JACK Connection's Audio tab and then reconnected it, the
crackling goes away. If I switch to another instrument in ZynAdd, however, I
have to repeat this process otherwise the crackling comes back.

Another thing I noticed is that if I turn on "Verbose messages" in JACK,
normally I'll steadily get line after line of messages like this:

> load = 13.6919 max usecs: 185.000, spare = 1148.000
The load number will increase and the spare will decrease as I play notes.
If I switch instruments in ZynAdd however, I get an Xrun and then the load
number goes way down in the 1.0 - 2.0 range and as I play notes in ZynAdd,
this number is unaffected. Its as if JACK disconnects itself from ZynAdd or
something, despite not giving any indication that it has done so.

Oh well. I'm content with this workaround. I just thought I'd post this info
in case it may be helpful for someone else.

On Fri, Jun 20, 2008 at 8:03 PM, Peter Lutz <peter at gotsomeideas.com> wrote:

> On Fri, Jun 20, 2008 at 6:40 PM, Norval Watson <norv2001 at yahoo.com.au>
> wrote:
>> Are you running a real-time kernel (rt)?
> Yes, I am. It's the default kernel in Ubuntu Studio. I get almost no Xruns
> in JACK too, so as far as I know, its a separate problem. I have noticed
> though that one of the few times I'll get one or two Xruns is when I switch
> instruments within ZynAddSubFX. Not sure if that matters.
> In case its helpful, here's some of my JACK settings:
>> Realtime: checked
>> Monitor: checked
>> H/W Monitor: checked
>> H/W Meter: checked (I'm not sure why I have these last two boxes checked,
>> does it matter?)
>> Frames/Period: 64 (I've tried 128 too, and that didn't seem to change
>> anything with ZynAdd)
>> MIDI Driver: seq
>> Sample Rate: 48000
>> Periods/Buffer: 2
>> Port Maximum: 256
>> Timeout: 500
> As for ZynAddSubFX settings, here's some of the relevant ones:
>> Sample Rate: 48000
>> Buffer Size: 256
>> OscilSize: 512
>> PADsynth Interpolation: Linear (fast)
>> Append: checked
>> XML compression level: 3
> Any ideas?
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