Codec2 and modem on a raspberry pi?

Encouraged by early success with FreeDV digital voice with codec2 it occurs to me that a great project would be to build the equivalent of these AOR digital voice modems. Looks like they sell for US$449 so to build something functionally equivalent based on a $38 Raspberry Pi is very attractive.

There's an interesting thread on the codec2 mailing list about running codec2 on a raspberry pi.

I imagine AOR are not too pleased about this prospect - if they are watching the road ahead, they would be working to build codec2 right in and they will pick up a potentially interesting early adopter market.

Looks like I'm not alone and ON1ARF is already working on this. Although he's using a pandaboard for decoding at this point.

We are at a fascinating time in Amateur Radio.

Update - audio on Raspberry Pi

Downloading and installing codec2 on the raspberry pi couldn't be simpler:

• sudo apt-get install subversion
• svn co https://freetel.svn.sourceforge.net/svnroot/freetel/codec2-dev codec2-dev
• cd codec2-dev
• ./configure
• make

To get the play utility, install sox:

• sudo apt-get sox

The test that encodes and then decodes out to the rpi's built-in audio works great:

• cd src
• ./c2enc 1400 ../raw/hts1a.raw - | ./c2dec 1400 - - | play -t raw -r 8000 -s -2 -

Next step, where I'm a bit stuck at the moment, is to record audio from an external USB headset. I plugged it in and you can list devices as follows:

• arecord --list-pcms

My USB Headset is a little Sennheiser one, so I get:

$ arecord --list-pcms

null

    Discard all samples (playback) or generate zero samples (capture)

sysdefault:CARD=headset

    Sennheiser USB headset, USB Audio

    Default Audio Device

front:CARD=headset,DEV=0

    Sennheiser USB headset, USB Audio

    Front speakers

surround40:CARD=headset,DEV=0

    Sennheiser USB headset, USB Audio

    4.0 Surround output to Front and Rear speakers

surround41:CARD=headset,DEV=0

    Sennheiser USB headset, USB Audio

    4.1 Surround output to Front, Rear and Subwoofer speakers

surround50:CARD=headset,DEV=0

    Sennheiser USB headset, USB Audio

    5.0 Surround output to Front, Center and Rear speakers

surround51:CARD=headset,DEV=0

    Sennheiser USB headset, USB Audio

    5.1 Surround output to Front, Center, Rear and Subwoofer speakers

surround71:CARD=headset,DEV=0

    Sennheiser USB headset, USB Audio

    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers

iec958:CARD=headset,DEV=0

    Sennheiser USB headset, USB Audio

    IEC958 (S/PDIF) Digital Audio Output

Copy the device name from the list above and use it in arecord and aplay below. To record 10 seconds of audio from the USB headset:

• arecord -D sysdefault:CARD=headset -d 10 test.wav

To play that back to the USB headset:

• aplay -D sysdefault:CARD=headset test.wav

I can hear my voice but it sounds terrible. It would be an abuse of codec2 to use it as input. Any tips would be appreciated!