{"id":4408,"date":"2025-12-14T13:50:45","date_gmt":"2025-12-14T13:50:45","guid":{"rendered":"https:\/\/m0aws.co.uk\/?p=4408"},"modified":"2025-12-15T08:03:22","modified_gmt":"2025-12-15T08:03:22","slug":"freedv-audio-routing-with-pihpsdr-and-hermes-lite-2","status":"publish","type":"post","link":"https:\/\/m0aws.co.uk\/?p=4408","title":{"rendered":"FreeDV audio routing with PiHPSDR and Hermes Lite 2"},"content":{"rendered":"\n

I’ve recently been trying out the FreeDV<\/a> RADEv1 digital voice mode on the HF bands with great success. The audio quality is astounding when compared to the normal analog SSB mode. Using only 20w I’ve been surprised how successful I’ve been talking to stations in the UK and Europe as can be seen in my FreeDV Log<\/a>.<\/p>\n\n\n\n

FreeDV has been around for quite a few years with development being funded by an ARDC<\/a> grant and financial sponsorship from the Software Freedom Conservancy.<\/a><\/p>\n\n\n\n

So what is FreeDV<\/em><\/strong>?<\/p>\n\n\n\n

To quote the FreeDV website<\/a>:<\/p>\n\n\n\n

“FreeDV is a suite of digital voice modes for HF radio. Our flagship mode is the Radio Autoencoder (RADE)<\/a>. You can run RADE using a free GUI application for Windows, Linux and macOS that allows any SSB radio to be used for high quality digital voice.<\/em>“<\/p>\n\n\n\n

And the most important part:<\/p>\n\n\n\n

“All software is open source, released under the (a) GNU Lesser Public License version 2.1 (GUI and legacy FreeDV modes) and two-clause BSD license (RADE).<\/em>“<\/p>\n\n\n\n

\"FreeDV<\/a>
FreeDV running under KDE-Plasma on Kubuntu PC<\/figcaption><\/figure>\n\n\n\n

Looking at the digital voice (DV) community in the HAM Radio world, it’s stuffed full with proprietary DV modes from small software houses and black box transceiver manufacturers with no real OpenSource<\/a> alternatives, until now.<\/p>\n\n\n\n

Installing FreeDV is pretty simple regardless of which operating system (O\/S) you use. Being a Linux<\/a> user I grabbed the AppImage from the website<\/a> and set about reading up on how it works and how it is configured.<\/p>\n\n\n\n

I decided to take the two sound card approach since I have 2 USB sound cards connected to my shack Kubuntu Linux<\/a> PC.<\/p>\n\n\n\n

Configuring the audio routing isn’t straight forward as both the receive and transmit audio to\/from the radio needs to be routed via the FreeDV app. To make this even more complicated I am using my Hermes Lite 2 SDR transceiver<\/a> and PiHPSDR<\/a> software, a complete OpenSource\/OpenHardware <\/em><\/strong>Amateur Radio Station.<\/p>\n\n\n\n

\"M0AWS<\/a>
M0AWS FreeDV and PiHPSDR Audio Routing Diagram<\/figcaption><\/figure>\n\n\n\n

Trying to clearly describe the audio routing using words alone would be impossible and very confusing so, I put together the diagram above.<\/p>\n\n\n\n

Using two USB sound cards I’ve configured the system such that USB Sound Card 1 (an old Griffin iMic USB sound device) handles just the audio from\/to the headphones and microphone. All the audio at this point in the system is analogue.<\/p>\n\n\n\n

The second USB sound card, a cheap Plug and Play (PNP) USB audio device from Amazon, handles all the digitised signals from\/to FreeDV and PiHPSDR.<\/p>\n\n\n\n

Taking this 2 sound card approach keeps confusion to a minimum and separates the analogue and digital components of the audio routing.<\/p>\n\n\n\n

So, how does this translate to the FreeDV and PiHPSDR audio settings?<\/p>\n\n\n\n

Transmit Audio Chain<\/h2>\n\n\n\n

FreeDV Transmit Audio Settings<\/h3>\n\n\n\n

Starting at the beginning of the transmit audio chain, let’s look at the transmit<\/em><\/strong> audio settings in FreeDV<\/em><\/strong>.<\/p>\n\n\n\n

Looking at the FreeDV Transmit<\/em><\/strong> audio settings screenshot below we can see that the
Input From Microphone to Computer<\/em><\/strong> device is set to:<\/p>\n\n\n\n

alsa_input.usb-Griffin_Technology_Inc_iMic_USB_audio_system-00.analog-stereo<\/code><\/pre>\n\n\n\n
This is the microphone connection on the iMic USB device (USB Sound Card 1) and is the analogue transmit audio<\/em><\/strong> input to FreeDV<\/em><\/strong>.<\/p>\n\n\n\n
The Output From Computer to Radio<\/em><\/strong> device is set to:<\/p>\n\n\n\n
alsa_output.usb-0c76_USB_PnP_Audio_Device-00.analog-stereo<\/code><\/pre>\n\n\n\n
This is the digitised audio output<\/em><\/strong> from FreeDV<\/em><\/strong> (via USB Sound Card 2) to PiHPSDR<\/em><\/strong> and is used as the transmit audio that is sent to the Hermes Lite 2 transceiver.<\/p>\n\n\n\n
\"FreeDV<\/a>
FreeDV Transmit Audio Settings<\/figcaption><\/figure>\n\n\n\n
PiHPSDR Transmit Audio Setting<\/h3>\n\n\n\n
To complete the transmit<\/em><\/strong> audio path we next need to look at the PiHPSDR<\/em><\/strong> transmit audio setting.<\/p>\n\n\n\n
\"PiHPSDR<\/a>
PiHPSDR Transmit Audio Settings<\/figcaption><\/figure>\n\n\n\n
As can be seen in the screenshot above, the Local Microphone<\/em><\/strong> device in PiHPSDR<\/em><\/strong> is set to the Monitor of USB PnP Audio Device Analogue Stereo<\/em><\/strong>.<\/p>\n\n\n\n
This effectively routes the digitised output<\/em><\/strong> audio from FreeDV<\/em><\/strong> (Output From Computer to Radio device) to the Input audio of PiHPSDR.<\/p>\n\n\n\n
The reason for using the Monitor<\/em><\/strong> audio feed is because FreeDV does not recognise the Mic Input<\/em><\/strong> in PiHPSDR<\/em><\/strong> as a valid output device for FreeDV to use, hence we just need to monitor the FreeDV output device and use it as our input audio device in PiHPSDR.<\/p>\n\n\n\n
This completes the transmit<\/em><\/strong> audio chain.<\/p>\n\n\n\n
Receive Audio Chain<\/h2>\n\n\n\n
PiHPSDR Receive Audio Setting<\/h3>\n\n\n\n
Starting at the beginning of the receive audio chain we first look at the PiHPSDR receive audio setting.<\/p>\n\n\n\n
\"PiHPSDR<\/a>
PiHPSDR Receive Audio Setting<\/figcaption><\/figure>\n\n\n\n
In the screenshot above we can see that the receive audio output from PiHPSDR<\/em><\/strong> is set to
USB PnP Audio Device Analogue Stereo<\/em><\/strong> (USB Sound Card2). This is the DX station’s digitised audio as received by the Hermes Lite 2.<\/p>\n\n\n\n
FreeDV Receive Audio Settings<\/h3>\n\n\n\n
Next let’s look at the receive<\/em><\/strong> audio setting in FreeDV<\/em><\/strong>.<\/p>\n\n\n\n
\"FreeDV<\/a>
FreeDV Receive Audio Settings<\/figcaption><\/figure>\n\n\n\n
The Input To Computer from Radio<\/em><\/strong> device is set to the monitor<\/em><\/strong> of the 
USB PnP Audio Output  Device<\/em><\/strong>:<\/p>\n\n\n\n
alsa_output_usb_0c76_USB_PnP_Audio_Device-00.analog-stereo.monitor<\/code><\/pre>\n\n\n\n
This effectively routes the digitised<\/em><\/strong> audio output from the  PiHPSDR<\/em><\/strong> receiver to the digitised audio input of FreeDV<\/em><\/strong>.<\/p>\n\n\n\n
Once again we have to use the monitor<\/em><\/strong> of the USB PnP Audio Output device as FreeDV does not recognise the PiHPSDR output as a valid input device.<\/p>\n\n\n\n
Next, the Output From Computer To Speaker\/Headphones<\/em><\/strong> device is set to:<\/p>\n\n\n\n
alsa_output.usb-Griffin_Technology_Inc_iMic_USB_audio_system-00.analog-stereo<\/code><\/pre>\n\n\n\n
This is the analogue audio output on the iMic USB Sound card (Sound Card 1) that routes the analogue audio to the headphones and completes the receive<\/em><\/strong> audio chain.<\/p>\n\n\n\n
Summary<\/h2>\n\n\n\n
The audio routing required by FreeDV can appear very daunting when first attempting to configure it on the Linux platform but, hopefully the diagram and screenshots above will help in understanding the complete end-to-end audio chain that is required to make this mode work.<\/p>\n\n\n\n
PiHPSDR can of course be replaced by your black box radio CODEC entries that will appear in the device lists shown above if you have your radio connected via USB. The config is basically the same but, just uses a different device instead of USB sound card 2 shown in the diagram above.<\/p>\n\n\n\n
I hope this article is useful to those wanting to try FreeDV on the Linux platform and I look forward to hearing you on RADEv1.<\/p>\n\n\n\n
More soon …<\/p>\n","protected":false},"excerpt":{"rendered":"
I’ve recently been trying out the FreeDV RADEv1 digital voice mode on the HF bands with great success. The audio quality is astounding when compared to the normal analog SSB mode. Using only 20w I’ve been surprised how successful I’ve been talking to stations in the UK and Europe as can be seen in my … <\/p>\n
Continue reading “FreeDV audio routing with PiHPSDR and Hermes Lite 2”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[54,58,132,163,535,20,329,534,334,42,532,4,536,399,455,407,409,410,171,38,456,309,310,538,135,400,134,170,345,533,443,5,539,537,258,215],"tags":[],"class_list":["post-4408","post","type-post","status-publish","format-standard","hentry","category-audio","category-audio-codec","category-debian","category-devices","category-digil","category-digitalmodes","category-digitalvoice","category-digiu","category-dv","category-dx","category-freedv","category-ham-radio","category-headphones","category-hermeslite2","category-hfbands","category-hl2","category-kde","category-kde-plasma","category-kubuntu","category-linux","category-linuxmint","category-mic","category-microphone","category-openhardware","category-opensource","category-pihpsdr","category-projects","category-pulse-audio","category-pulseaudio","category-radev1","category-receiver","category-sdr","category-soundcard","category-speaker","category-ssb","category-ubuntu"],"_links":{"self":[{"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/4408","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4408"}],"version-history":[{"count":67,"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/4408\/revisions"}],"predecessor-version":[{"id":4486,"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/4408\/revisions\/4486"}],"wp:attachment":[{"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4408"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4408"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/m0aws.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4408"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}