This afternoon at eComm 2009, Skype will formally announce that it is making its in-house developed SILK wideband voice codec available royalty-free. Yes, free, for incorporation into any third-party application or device.

By offering SILK broadly in a very “open way, royalty free” to any third party developer, Skype thinks it can “unlock one of the major obstacles in the migration from narrowband video,” said Skype GM Jonathan Christensen.

SILK is designed as an Internet-specific speech codec able to work with variable bit rates. At its highest “superwideband” rates, it samples at 24 kHz, providing 12 kHz effective voice. It’s designed to be scalable from 6 Kbps to 40 Kbps with very low delay, low CPU and memory consumption, and it’s designed to be “very robust” for jitter and packet loss. The codec is written in fixed-point ANSI C, so it can run on basically any platform.

In comparison, the traditional PSTN delivers voice at an “effective bandwidth” of around 3 kHz – sometimes a lot less when you move to mobile phones and/or transcoding involved for long-distance transport. More recent “traditional wideband” codecs provide around 7 kHz effective bandwidth, with Skype’s earlier codec delivering 8 kHz effective using 16 kHz sampling.

Christensen said SILK had been independently tested against other various popular codecs with “very favorable” results. Using MOS scores, SILK performed better than other codecs at various bit rates and every percentage of package loss.