Remote Audio Codec

Paul Christensen, W9AC

Looking to determine the type of audio CODEC being used with SSDR's remote audio mode.  Remote audio isn't as clear as main headphone audio, presumably because the main headphone feed is sourced from the DAC. 

Whether through Maestro, K6TU's app, or SSDR loaded on a tablet PC and accessed over LAN, audio sounds dirty with a noise component.  It's subtle for sure, but there nevertheless.   

Possibly at some point in the distant future we can have a choice in CODECs, much like the RemoteRig product where one of several different CODEC options can be selected to best work with the connection rate.

Paul, W9AC   

  

Jim Gilliam

I have noticed when I use a CODEC with my Flex 3000/5000 for remote operating like RemAud, the audio is considerably cleaner than that of the Flex SmartSDR remote audio.

Jim, k6QE

Tim - W4TME

OPUS https://www.opus-codec.org/

Paul Christensen, W9AC

Thanks Tim.  It seems like scaling is inactive? Over LAN, it should scale closer to the audiophile rates shown below but of course subject to latency concerns with higher rates.  Are sample and bit rates fixed at the moment?

"Opus can scale from low bitrate narrowband speech to very high quality stereo music. Supported features are:

• Bitrates from 6 kb/s to 510 kb/s
• Sampling rates from 8 kHz (narrowband) to 48 kHz (fullband)
• Frame sizes from 2.5 ms to 60 ms
• Support for both constant bitrate (CBR) and variable bitrate (VBR)
• Audio bandwidth from narrowband to fullband"

Tim - W4TME

There seems to be a bug in that part of the OPUS code.  We are looking into it as it will become important in SSDR v2.0

Varistor

While the codec is important to know, it is more important to know what use cases and design requirements have been assumed to select and configure the codec. These will be dramatically different between LAN and WAN use. Also, it would be great if the use has the ability to select fixed vs. variable bit rate, mono vs. stereo, etc.

For example, you don't really need anything beyond 8 kbps VBR mono for CW, while you would need a lot more for ESSB or FM.