PC Audio latency and noise

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  • Updated 3 months ago
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As anyone noticed any latency or some digital noise (clicks) when selecting PC audio to run Flex audio to PC speaker or PC headphones. I don’t use it very often and this is the first time with V2, but I recalling to working well on V1.

Running Win 7 and V 2.1.33. Just curious if it works fine for other folks before I dive into driver/PC issues.

Thanks
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Steve

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Posted 3 months ago

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Tim - W4TME, Customer Experience Manager

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Official Response
The quality of PC Audio is dependent on several factors that FlexRadio has no control over. 

First is the network connection.  The audio data is compressed by the OPUS codec and transferred from the radio to SmartSDR for Windows running on your PC using the VITA-49 data stream.  Any network delays or latency can cause issues.  If any part of the connection between the radio and SmartSDR is wireless, this too can be a problem because wireless networks provide convenience over network reliability (and the connection is not full duplex and throughput is degraded by each wireless device on the access point). Dropped packets will result in audio dropouts that may sound like "pops" in the recovered audio.  When quickly moving the panadapter back and forth (tuning the panadapter), it generates a lot of additional network traffic between the radio and the PC and that can exacerbate the issue if the network is not performing optimally.

Second, once the audio data is delivered to the PC, the audio data is uncompressed by the OPUS codec on the client and then passed to the Windows sound subsystem.  At this point, the quality is completely dependent on the PC sound card and the hardware drivers that it uses to interface with the PC operating system.  All of these processes take time to complete their processing and create latency.  In addition, when the sound card (and the network interface) are used, there will always be DPC latency (https://helpdesk.flexradio.com/hc/en-us/articles/202118398-What-are-DPCs-and-why-do-they-matter-) and this too creates more delays in processing the audio.

PC Audio works well with no apparent latency or dropped audio packets with a properly performing network and a PC that is also working well.  I test software and issues on an 8-year-old 4 core AMD machine that has very low  DPC latencies (<250 Us) under load and connected to a quality Ethernet Switch (Cisco Small Business).  Using the latest SmartSDR software, I tried to replicate the problem of audio pops by "thrashing" the panadapter back and forth as Dan indicated.  I heard no audio dropouts or other issues related to audio latency using PC Audio.  So I do not think the issues you are experiencing are systemic but more environmental and related to the issues I noted above.
(Edited)