An Open-Source Speech Codec at 450 bit/s with Pseudo-Wideband Mode

Most modern digital speech codecs are proprietary and do not give insights into their implementations. “Codec 2” is an open-source codec and opens up the possibility of application-tailored adaptations. In this publication a new 450 bit/ s mode is introduced. It includes a pseudo-wideband mode that can be optionally enabled at the receiver without resulting in a higher bit rate. By sorting the codebook vectors a bit error rate of 10
^-1
is still intelligible. An encoded audio transmission was tested with two low-power Sub-GHz transceivers in the 70 cm amateur radio band achieving a sensitivity of -130 dBm. For proofing the concept, a field test was conducted and compared to a propagation simulation.