Codec2: GNU Low-bitrate Speech Codec

Low bandwidth speech compression is a desirable concept for amateur radio enthusiasts. Unfortunately there isn’t a great open-source option out there, but that’s changing with the low-bitrate speech compression package called Codec2. It manages to transmit and decode at 2550 bits per second with results comparable to proprietary solutions like MELP and very near the initial goal of 2400 bit/s. [David Rowe], who spearheads the project, has been simulating communications using a Linux box and has posted audio snippets at the first link above for comparison. They’re looking for feedback and testing so if you interested give them a helping hand.

[Thanks Robomo]

11 thoughts on “Codec2: GNU Low-bitrate Speech Codec

  1. This is great and exactly what we need. There’s been talk on the mailing-list that ended up with support in freeswitch for this codec. I hope they can eventually figure out a modification for the dstar modules for the radios that take them to allow this codec to run in a real radio at some point.

  2. Sounds pretty good, I wish them luck.

    Regarding the radios; The UT118 plugs into a socket which has a I2C(?) control from the radio’s CPU and insert lines to the RX/TX audio.

    If someone really wanted to they could produce an alternative plug in module to support any new codecs they wanted.

    Also the DStar protocol has a byte allocated in the data frame for CODEC version. One could (ab)use this to indicate an alternate CODEC.

  3. @Ugly American, Doc Oct:

    My understanding is that the problem with Speex isn’t so much that it’s not good at low bitrates, it’s more about the error handling. The way I understood it, Speex was designed for VoIP. And with VoIP, your error correction is going to be for missing packets. With codec2 (and ham radio codecs in general), you’ll want something that can correct for missing/incorrect bits. There’s no guarantee (hell, it’s pretty unlikely) that the entire packet will arrive intact.

  4. Another example of a hams advancing the radio art.

    Nobody tell @osgeld. If he found out that Dave Rowe was not a grumpy old man with a preoccupation with kids walking on his lawn, he might self-destruct.

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