[Skimmertalk] CW skimmer audio output stutters under load

bubnikv . bubnikv at gmail.com
Fri Aug 14 05:57:19 EDT 2015

Hello Pete.

Thanks for your response.

> Vojtech, I suggest you write directly to Alex VE3NEA about this.  To my
knowledge, he is the only one who fully understands the internals of CW

I did. He usually responds very quickly and precisely to my technical
details, but this time he seems to be busy.

> I'm wondering, though, whether your 2007 PC may have USB 1.0 ports,
instead of USB 2.0.  If so, that could impose some pretty severe
limitations on throughput.  Can you try it with the laptop's internal sound
components at 48 or 96 KHz, whichever it supports, and see whether you
still have the glitches.

The internal sound card is mono only and it does not even support WDM. The
USB ports support 2.0. I made sure the sound card is the only device on the
computer internal USB hub.

I tried the DPC latency checker tool and found out, that 4ms glitches are
caused by a deferred procedure call of some badly written driver. Then went
on to disable various drivers in the Device Manager one by one. It seems
the WiFi driver and the various VAC drivers were the worst offenders. The
WiFi driver caused latency spikes even with WiFi off.

Now the CW Skimmer audio behaves better, but I still get short drop offs
when I move a mouse or scroll the waterfall. I will try some additional
analysis tools to verify, whether the Intel integrated video driver is the
culprit after I disabled the WiFi driver. I will report to the group.

DPC latency checker:

Latency Monitor:

I may lower the system latency to some extent by tinkering with the
drivers, but it would still be great, if the CW Skimmer software offered an
audio buffer settings to overcome these badly written drivers.

73, Vojtech OK1IAK

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