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

The 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 GM 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 Skype for Mac in the near future. But the the SILK codec has been modularly designed for embedding into silicon; we can expect 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?

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Skype for Windows 4.0 Goes Gold; Improved UI, Audio and Video Performance

Over the past eight months 1.2 million Skype users have participated in the Skype for Windows 4.0 beta program (stage 1, stage 2, stage 3). During this beta period, not only current user feedback was sought but also feedback from new users installing Skype for the first time. The goal was to provide a user interface that was more intuitive while encouraging users to go beyond simply voice calls to experience and use chat and video conversations. Today Skype is announcing the Gold release of Skype 4.0 for Windows. From the download page:

We've built this brand new Skype so you can have the conversations that make a difference to you, every day. It's easy to use, plus step-by-step guides help you get started.

While most of the new features have been revealed during the beta period, Skype's marketing will focus on three key features:

• New user interface; with over 25% of Skype-to-Skype calls involving video this new release has been designed with a focus on improving the video call user experience.
• Improved call quality: Skype 4.0 for Windows incorporates Skype's new SILK codec whose features are discussed in a separate post today. Bottom line is a crisp, crystal clear audio experience, yet only half the network bandwidth of other codecs is required to support a voice call.
• Bandwidth management: a new bandwidth manager has been developed with the goal of improving overall call performance by adapting, in real time, to degraded or low speed network conditions, such as those caused by excessive packet loss and/or jitter.

The new user interface also has taken into account factors that encourage users to explore Skype beyond voice calling. Incorporating beta user feedback Skype has found that the new UI is driving up adoption rates for Instant Messaging, file transfer and video. When you open a contact window launching a voice, chat or video conversation requires a single click on the respective voice ("Call"), chat or video button. The associated text pane tracks not only chat messages but also voice and video call detail information (launch time, end time) as well as file transfer information. And, as in the past with chat, the entire record is all archived on your local PC for future recall.

Other features: You can choose to view your Skype activity in one larger window or in individual "conversation" windows. During a call a drop down menu on the "call audio control bar" provides quick access to making any necessary audio or video settings. Single click buttons allow you to quickly change or add conversation modes to adapt to the context of the conversation. A wizard provides assistance with testing audio and video settings. During their testing they found that these features drove new users to more quickly experience chat and video while there was an increase in usage of these modes by legacy users.

On-the-fly the bandwidth manager can adjust both video and audio transmission by making real time adjustments to parameters such as video resolution, frames-per-second or audio bandwidth. to ensure an ability to maintain a basic level of communication while enduring these conditions. When combined with SILK's reduced network bandwidth requirements, the overall goal is to improve the overall user experience with minimum or no user intervention required.

Two changes;

• The SkypeMe! status button has been removed as a result of its tendency to be used for spamming and other forms of unwanted calls. (Of course you also still have the option to only allow callers in your Contact list to call you.). Along with this Skype has introduced "abuse reporting" which is monitored by Skype personnel for dealing with undesirable calling activity.
• While you can still participate in Public Chat sessions launched or joined from Skype 3.8, there is still no ability to launch or join a Public Chat from Skype 4.0 for Windows. This is my primary complaint about the new user interface. We have had a Skype 4.x Public Chat discussion ongoing since May, 2007; it has provided an interesting dialogue amongst Skype users and Skype personnel, including some feedback on features in Skype 4.0. And it has supported many other informal "water fountain" conversations amongst special interest communities of Skype users. Skype for Windows Product Manager Mike Bartlett claimed yesterday, during an interview, that Skype was reviewing how to embark on "public conversations" in today's messaging world where services such as Twitter and Friend Feed also provide ongoing dialogues. However, Skype Public Chat has its own "space" in terms of user community; it needs to be brought back as soon as possible.

Over the next few weeks, with more experience using Skype 4.0 for Windows we may cover some features in more detail. In the meantime you can download it here. We look forward your feedback in the Comments.

Yesterday Skype went past 16 million concurrent users around 1830 GMT. It will be interesting to monitor both the concurrent user number and Hudson Barton's "real user" indicator as Skype 4.0 for Windows installations grow over the next couple of weeks..

Of course, the best news is that Skype-to-Skype calls (including multi-party calls), chat and video calling remain free. And there are calling plan subscriptions available for low cost calling to landlines worldwide.

From the Release Notes:

• feature: New style when copying and pasting text in an instant message (text quoting)
• featue: Video Call in separate window
• improvement: Skype now creates thumbnails of display pictures
• change: Get more ringtones and custom sounds link removed from options panel
• change: Removed display bandwidth usage option
• change: Dial pad will be opened automatically on call to landlines or mobiles
• change: Increased minimum window size in compact mode

Other Posts:

• Product Manager Mike Bartlett: Skype 4.0 - It's All Yours
  
• Mike Bartlett Discusses Skype 4.0 Beta on Squawk Box
• Skype's videos about the 4.0 beta limited release
• Mike Bartlett Comments on Skype 4.0 User Feedback
• Mike Bartlett on Skype 4.0 Beta 1 Feedback

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Skype 4.0 For Windows Brings A Fresh New User Experience

With the rollout of the new 4.0 version of Skype for Windows, Skype has completely redesigned the user interface of the popular internet telephony and instant messaging platform. Skype has long had a user experience that is very familiar "instant messenger" look and feel, not all that different form other IM clients such as AOL Instant Messenger or Yahoo Messenger.

Redesigned For Usability

In an interview with Mike Bartlett, Director of Windows Product Management for Skype, he told me the new version of Skype was re-built from the ground up to enhance ease-of-use with regards to interacting with your contacts and getting Skype set up to use your microphone and webcam.

Skype version 4 uses a fresh user experience, incorporating more of a conversational point of view. When loading Skype 4.0 for the first time, users might be shocked to be greeted with a client that takes up much more screen real estate than before. The new Skype version is tailored around those who hold open multiple IM conversations, calls, video calls, and file transfers in one horizontally arranged tabbed window. Before this new user experience was integrated into Skype, users were required to manage multiple windows for each open conversation.

Have Your Conversation Your Way

The new Conversation Tabs is aimed at make it easy to manage multiple conversation and IM streams in a single window. By separating the open conversations away in a separate tab than your contact list, Skype has made it very easy to track open communications, whether they are IM conversations, voice calls or video calls. Of course, if you don't like the Conversations view, you can switch to Compact view that will separate each active contact into it's own window, much like the classic Skype client versions.

As you can see in the screenshot, video calling is a major component of the new user interface. A prominently placed video call button is present when conducting an IM conversation. Also, another very useful feature: conversations with new unread messages or actions will flash orange to draw your attention to the new messages, whether they are from an individual or in a group chat.

Also, with a single click on a Skype contact, you reveal the various options. These options before were hidden behind the right-click context menu, as Skype was centered around voice communications in prior versions. The new version helps bring to life the various contact options that have always been available.

Summary

While Skype 4.0 on Windows took a while to get used to, I see the usefulness in the conversational views and refreshed user experience. In fact, I recently went back to a computer that is running an older 3.0 version of Skype and missed the conversational changes in 4.0 Also, being able to see freshly updated conversation items as they happen makes conversation tracking easier.

This post is written by Skype Journal columnist Jason Harris, an internet telephony writer and enthusiast.

To follow Jason further: check his website, follow him on Twitter. Also, you can reach Jason via Skype as harrisja or on his mobile at: +1 503 334 2574.