Skype will license a high-quality audio codec in its latest VoIP (voice over Internet Protocol) software to any developer or vendor free of charge, the eBay subsidiary announced Tuesday.

The codec, called Silk, can deliver sound quality that captures the full sound of the human voice, according to Jonathan Christensen, Skype's general manager of audio and video. This "super-wideband" codec was introduced with the Skype 4.0 for Windows client, announced last month. Christensen unveiled the licensing program, which is live now, at the eComm conference in Burlingame, California.

The traditional phone system uses a narrow band for voice, from 400Hz to 3,400Hz, that cuts off high and low frequencies. This allows voice to be carried in a standard 64Kb per second (Kbps) channel but has disadvantages, such as blurring the difference between similar sounds such as "f" and "s."

VoIP can be carried on a fatter pipe than 64Kbps, so new codecs have been written to encode and decode voice at higher quality. With Silk, Skype can now reproduce the full range of typical voice frequencies audible to the human ear, from 50Hz to 12,000Hz, Christensen said. This will help callers identify different speakers on conference calls and make calls sound generally warmer, he said. At the same time, the new codec uses 50 percent less network bandwidth than Skype's previous version.

The company is making the codec freely available to third-party developers so they can use it in any device or application, with or without Skype, Christensen said.

"We think this is a way the whole industry can come up to a new standard of voice quality," Christensen said.

Despite the fact that Silk represents "a very significant chunk" of Skype research and development investments, the company is releasing it in order to make its popular peer-to-peer voice application work with a wide range of hardware and software clients, Christensen said. Those could include PC software, headsets, videoconferencing systems, cordless phones and mobile phones. Skype counts among its partners Asustek Computer, Plantronics, Arm, LifeSize and HelloSoft. Plantronics is set to announce on Wednesday a headset with its own sound card, which can use the Silk codec, according to Christensen.

Without a common codec, it would be hard for Skype to make its software work with this range of clients, Christensen said. Coming to agreement on which codec to use, given different licensing requirements, would be too complicated, he said. Silk is intended as an easy one for partners to adopt.

Skype is also moving toward making Silk interoperate with endpoints using SIP (Session Initiation Protocol), the emerging standard for signaling on IP telephony networks. The company is talking with Digium, the distributor of the Asterisk open-source telephony platform, and wants to make deals with other partners like this, Christensen said.

Silk can run on x86 chipsets for Windows, Macintosh and Linux systems, and the software has been run on Arm and MIPS chip platforms, according to Skype.

In addition to Skype 4.0 for Windows, the high-quality codec is available on Macintosh beta version 2.8, with a final Mac version coming in April. Linux is on a similar timeline, Christensen said.