First test of Codec 2

I’ve previously mentioned David Rowe’s excellent work on a patent free codec for amateur radio, Codec2, but today is the first time I actually downloaded the code and gave it a shot. You can find the code and the quickstart here:

Codec 2 « Rowetel

My own voice has some fairly low frequencies in it, so I was intrigued to find out how my own voice would do. David’s page mentions that Kristoff, ON1ARF, has a voice where the existing AMBE voice encoder does a much better job, largely because the low frequency encoding of AMBE is much more effective, so I took a short message that I used for some companding experiments I did a while ago, and gave it a try.

The original, as recorded via my iPhone, and downsampled to 8khz using sox.
The same clip after encoding/decoding with codec2.

As you can probably tell, the fidelity isn’t all that stellar with my own voice either. I have nothing to add other than that base observation, but perhaps this will serve as incentive for me to look into this stuff more.

2 thoughts on “First test of Codec 2”

  1. Josh (KD8HRX) Smith

    Mark,
    Very cool stuff – codec2 is perhaps the most important amateur related projects going on right now. It’ll really be nice if it can replace AMBE in a DSTAR like network.

    73 DE KD8RHX

  2. David Rowe

    Hi Mark,

    Thanks for that test, yes Codec 2 sounds a bit rough with your voice. I can here the pitch estimator making errors. Also the level of your source speech is fairly low compared to some other samples.

    All excellent tests. This is what I love about open source DSP development – people stress code in unexpected ways which leads to improvements. This approach also worked very well with Oslec – the open source echo canceller I developed for Asterisk a few years ago.

    I’ll use your sample for some more development in a few weeks. By looking at the internal states of Codec 2 when processing your sample I will hopefully be able to improve it.

    I must also come up with a simulation for SSB and NBFM to use for comparisons. That is the speech quality target for Codec 2, e.g. it’s not meant to aim a MP3 quality. The upper limit would be cell phone quality.

    Cheers,

    David

Comments are closed.