After a little more experimenting, I found a little workaround for this issue... although it&#39;s still doesn&#39;t exactly shed any light on what&#39;s causing the problem. I figure I&#39;ll post it here to this mailing list, in case someone with more experience might know what&#39;s going on here.<br>
<br>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&#39;d start hearing the crackling sound. The crackling didn&#39;t show up at first, only until I switched instruments. I found that if I disconnected ZynAddSubFX from system in the JACK Connection&#39;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.<br>
<br>Another thing I noticed is that if I turn on &quot;Verbose messages&quot; in JACK, normally I&#39;ll steadily get line after line of messages like this:<br><blockquote style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;" class="gmail_quote">
load = 13.6919 max usecs: 185.000, spare = 1148.000<br></blockquote>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.<br>
<br>Oh well. I&#39;m content with this workaround. I just thought I&#39;d post this info in case it may be helpful for someone else.<br><br><div class="gmail_quote">On Fri, Jun 20, 2008 at 8:03 PM, Peter Lutz &lt;<a href="mailto:peter@gotsomeideas.com">peter@gotsomeideas.com</a>&gt; wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="Ih2E3d">On Fri, Jun 20, 2008 at 6:40 PM, Norval Watson &lt;<a href="mailto:norv2001@yahoo.com.au" target="_blank">norv2001@yahoo.com.au</a>&gt; wrote:<br>
</div><div class="gmail_quote"><div class="Ih2E3d"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;">Are you running a real-time kernel (rt)?</div></div></blockquote></div><div><br>
Yes, I am. It&#39;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&#39;ll get one or two Xruns is
when I switch instruments within ZynAddSubFX. Not sure if that matters.<br><br>In case its helpful, here&#39;s some of my JACK settings:<br>
<blockquote style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;" class="gmail_quote">Realtime: checked<br>
Monitor: checked<br>
H/W Monitor: checked<br>
H/W Meter: checked (I&#39;m not sure why I have these last two boxes checked, does it matter?)<br>
Frames/Period: 64 (I&#39;ve tried 128 too, and that didn&#39;t seem to change anything with ZynAdd)<br>
MIDI Driver: seq<br>
Sample Rate: 48000<br>
Periods/Buffer: 2<br>
Port Maximum: 256<br>
Timeout: 500<br>
</blockquote>
<br>As for ZynAddSubFX settings, here&#39;s some of the relevant ones:<br><blockquote style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;" class="gmail_quote">Sample Rate: 48000<br>

Buffer Size: 256<br>OscilSize: 512<br>PADsynth Interpolation: Linear (fast)<br>Append: checked<br>XML compression level: 3</blockquote><div><br></div></div></div>Any ideas?<br>
</blockquote></div><br>