SILK: Skype’s New Audio Codec Sets New Performance Standards for Voice Conversations

silklogo180px SILK: Skypes New Audio Codec Sets New Performance Standards for Voice ConversationsThe most recent hotfix release of Skype for Windows 4 Beta 3 had one key new feature:

  • feature: Super Wideband audio codec

The associated Skype Garage post went on to say:

… Starting from this version we’ve included the new Super Wideband Audio codec. This is our second in-house built audio codec especially designed for calls over the internet with superb quality. The Super Wideband Audio codec will help you most on lousy network conditions and when you have lower bandwidth available, although it also improves quality in normal conditions too.

Today Skype for Windows 4.0 Gold release will now allow the entire Skype for Windows user community to take advantage of the SILK codec’s features.

SILK is basically a significant improvement on Skype’s previously acclaimed HD Voice performance. I have now experienced a couple of calls where this SILK codec was available at both ends of the call; it certainly provides a clearer, crisper audio experience. (For those unfamiliar with the term “codec” they are algorithms engineered into the voice communications network for converting audio waveforms into digital streams for transmission over the communications network and then converting them back to an audio waveform at the receiving end.)

Last week I had the opportunity to interview Jonathan Christensen, Skype’s General Manager for Media Platform to learn more details about this “SILK” codec. This codec is the outcome of a three year development process with a focus on:

  • improving the audio bandwidth out to 12,000 KHz
  • providing bandwidth management to deal in real time with degraded  network conditions
  • balancing the codec optimization between voice, music and background noise, each of which can have an impact on the overall user experience
  • overall robustness to provide a more consistent user experience, regardless of network conditions and an individual caller’s voice signature.

While the human ear can hear sounds up to 22 KHz the actual sound produced by human vocal chords has a frequency range of 20 Hz to 14 KHz; however, sounds below 70Hz are not what you would call “pleasant” (as experienced with those “thump, thump” car speakers). Skype’s SILK codec is optimized for the transmission of audio between 70 Hz and 12 KHz. Compare this to the bandwidth of the PSTN’s standard G711 codec of 400 Hz to 3.4KHz; wider band codecs, such as AMR-WB and iSAC cover the range of 50 Hz to 7 or 8 KHz respectively. And, as indicated in both the AMR-WB and iSAC Wikipedia entries, there is a major licensing cost consideration:

AMR-WB has been standardized by a mobile phone manufacturer consortium for future usage in networks such as UMTS. Although its speech quality (similar to Skype, including glitches) makes it likely that older networks will have to gradually be transformed to support wide band, its high legal costs may limit its uptake.

However, in order to deliver on this audio bandwidth, Skype also had to consider getting the voice stream across the Internet. SILK interacts with Skype’s redeveloped (network) bandwidth manager that uses a feedback algorithm to provide “adaptive bandwidth management”. SILK is a “variable bitrate” codec that can scale the bitrate (amount of data being transmitted as voice packets) up and down as necessary. The key network parameters governing this adaptation are packet loss and jitter changes. Fundamentally, to the end user, this means incorporating a level of call robustness that results in improved consistency of call quality, especially for lower speed Internet connections (below 3Mbps) with no user intervention required.

Another factor to be considered are accommodations for differences in perception of audio quality depending on whether there is voice, music or random background noise involved in the audio signal. Suffice it to say that Skype’s engineers have been involved in a balancing act amongst these factors in the development of the SILK codec.

The bottom line is that Skype has set new barriers for voice call quality and and the associated user experience. Since there needs to be SILK at both ends of a call, the number of calls I have experienced with SILK has been limited but, as mentioned above, those I have made had a very crisp, clear audio quality. With Skype’s launch today of Skype for Windows 4 Gold release almost all my Skype-to-Skype calls will be able to achieve this performance level. Going forward expect to see SILK incorporated into ont only Skype for Mac. But the the SILK codec has been modularly designed for embedding into silicon; we can expect some future Skype-enabled hardware platforms to be able to take advantage of SILK’s performance.

And finally note that, in order to keep costs low while improving call quality, Skype has no licensing costs associated with their proprietary codec. Is there a potential for a new Skype revenue stream by licensing this codec to other communications service providers as well as hardware vendors?

About Jim Courtney

Bringing over thirty years' experience in the sales, marketing and management of cutting edge technology businesses.

, , , , , , , , ,

Trackbacks/Pingbacks

  1. My Final Skype Journal Post: Jim Courtney is moving on…. | Voice on the Web - February 16, 2009

    […] for Business, spoke about Skype’s goal to be "Better than a phone…". Today, with the SILK codec, Skype is much better than a phone; since its introduction I cringe politely when I have to go back […]

  2. eComm 2009: Sponsors Accelerating in a Depressed Economy | Voice on the Web - February 16, 2009

    […] SILK: Skype’s New Audio Codec Sets New Performance Standards for Voice Conversations (voiceontheweb.com) […]

  3. Digium Provides Progress Update on Skype for Asterisk | Voice on the Web - February 23, 2009

    […] set only shows support for narrowband audio G.711 and G.729 codecs. Will there be support of Skype’s SILK super wideband audio for calls routed through Skype for Asterisk that are effectively Skype-to-Skype calls once the end […]

  4. Skype for Mac 2.8 Beta 2 with SILK Codec | Voice on the Web - April 9, 2009

    […] Skype’s superwideband audio SILK codec is finally available for beta testing on Skype 2.8 for Mac Beta 2 released yesterday. I did a test call with Dan York yesterday where I was on a Windows PC with Skype for Windows 4.0 which supports SILK while Dan was using the new Skype for Mac 2.8 beta version. His subsequent Tweet, shown above on the right, says it all. I still cringe politely when not on a call with SILK support. […]

  5. Skype at eComm 2009: Royalty Free Licensing of SILK Codec | Voice on the Web - April 9, 2009

    […] the launch of Skype for Windows 4.0, Skype delivered its first client incorporating Skype’s new superwideband SILK codec providing a new user experience in voice calling. For example, Alec Saunders in “Skype 4.0 audio: […]

  6. New GIPS Customer Exemplifies The Voice Engine Market Opportunity | Voice on the Web - April 18, 2009

    […] the future, CommuniGate may elect to investigate Skype’s superwideband SILK voice codec for incorporation into their GIPS Voice Engine; however, as its royalty-free licensing had only […]

  7. Skype 4.1 Beta Launched: Will That Be Video or Desktop Sharing? | Voice on the Web - July 25, 2009

    […] addition to the updates to the audio and video engines (incorporating the SILK codec) , Skype 4.1 restores birthday reminders (if you want to keep your birthday private, simply don’t […]

  8. FREETALK® Everyman for Skype: Not Just Another Headset | Voice on the Web - August 14, 2009

    […] The recent introduction of Skype’s “superwideband” SILK audio codec, supporting a 12KHz audio bandwidth, has set new bars for incorporating HD Voice performance into a headset – both the speakers and the mic. […]

  9. Update Fever at Skype Again | Voice on the Web - September 7, 2009

    […] when launched it was mentioned that the SILK codec was “modularly designed for embedding into silicon”. We have also seen its migration into Skype […]

  10. FreeTalk Freedom Wireless Stereo Headset "2.0" – When You Just Can’t Sit Still During a Skype Call | Voice on the Web - November 20, 2009

    […] supported the various wideband codecs that Skype has provided over the past two years, including the recently released SILKTM codec with its support of 12KHz audio for Skype calls. In fact, when Skype provided me with samples of […]

  11. Coming Real Soon Now: Skype for iPhone over 3G | Voice on the Web - February 3, 2010

    […] high quality audio SILK technology will be embedded in the next version of Skype for iPhone (for both the iPhone and iPod […]

  12. Skype’s SILK Codec: Working Towards Adoption as a Standard | Voice on the Web - March 11, 2010

    […] licensing of the SILK codec. Since then it has been incorporated into all subsequent releases of Skype for Windows 4.x, Skype for Mac 2.8 and Skype for Linux. Recently Skype announced that the SILK codec will be […]

  13. Compact Audio: Yamaha SoundGadget USB Microphone Speaker Opens New Experiences for Road Warriors | Voice on the Web - May 23, 2010

    […] purposes, that the microphone supports Skype calling up to 7Khz – sufficient to take advantage of Skype’s wideband SILK codec feature; however, this limitation is removed for “local” voice or music […]

Leave a Reply