PC Audio latency and noise

Steve · May 2018

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

Mark K1LSB · May 2018

Steve,

I have observed some objectionable transmitted noise related to what I believe is un-flushed mic buffer that is aggravated when selecting PC audio, but I don't want to muddy the picture with problems unrelated to what you're seeing so could you please expound on exactly what the problem is you're seeing?

Thanks,

Mark K1LSB

PS The reason I haven't posted about my own problem yet is because I've been doing experiments over the past couple of weeks to nail down specifically what the problem is and isn't. I'll either post up about my findings shortly in a separate thread or simply open a Help Desk ticket. It's a rather glaring problem and I've been able to replicate it with SSDR V1 and V2 and a friend has been able to replicate it on his 6600M (I have a 6300), so the problem spans multiple hardware and software platforms. I'm actually surprised no one has mentioned it before.

danparsons · May 2018

I am experiencing the same problem on my 6600M. So far no idea how to fix it. This is only on SmartSDR for Windows, I do not have this problem with the iOS version, or with dogparkSDR on Mac. Only the native FlexRadio Systems-created version has the issue.

danparsons · May 2018

Dragging the panadapter back and forth aggressively seems to exacerbate the issue. (Again, only on Win10 + SmartSDR)

Bill -VA3WTB · May 2018

It sounds to be a byproduct of using the PC for audio. Now you are using the PC processing for audio, an added link. It is the same as using remote in this case.

danparsons · May 2018

I agree, but none of my other remote clients (SmartSDR for iOS; dogparkSDR for macOS; and the front panel of the 6600M is a remote client too) have the problem.

Doug Hall · May 2018

Make sure the sample rate on your Windows playback device is set for 48 kHz and not 44.1 kHz. On my system 44.1 kHz produced occasional clicks and pops in the audio when using PC audio.
73,
Doug K4DSP

Tim - W4TME · May 2018

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.

PC Audio latency and noise

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