Skype 4.0 (download) became available for free on Tuesday to Windows users. The free desktop VoIP communicator is a worthy final version that brings some key enhancements with video and audio bandwidth, though it leaves behind some of the extra adornments of version 3.8, the last stable build.

Those who have been following the triple release of betas since the summer won’t see more than a few changes. If 4.0 is new to you, however, the developments are more notable.

Skype concentrates on video size, quality, and performance in this version. From version 3.8 to version 4.0, every design change has been made to draw video and IM to the forefront, and for the most part it works. The video window has expanded and calls are easier to start. The classic two-pane interface has consolidated into one, though you can still split them apart if you prefer.

Skype’s beautifully staged marketing shot shows Skype 4.0′s new videotopia.

(Credit: Skype)

As the culmination of the beta series, Skype 4.0 gets a pumped-up video and a completely new audio engine. Compared with other codecs out there, the new audio engine, named Silk, is touted to give Skype superwide-band audio (which operates like broadband), but uses half the bandwidth. Fewer bandwidth demands gives Skypers with dial-up connections (like a lot of people in India and Brazil) a bigger boost, keeping calls from being dropped or mangled beyond recognition.

I’ll attest to the great call quality during my interview with Skype’s London-based product manager. It was clear and the vocal timbre sounded true. Keep in mind that I dialed in from a newish, memory-loaded Asus computer with full broadband support and a set of top-tier headphones. Quality will still depend on your Internet connection and hardware configuration. Using headphones that support ultra-wideband audio will help.

The video stream was similarly good. Though far from the perfection of TV, I noticed fewer jumps and blips and sound syncing that was very close to real-time. Problems that have beset Skype’s video calls in the past–a frozen or choppy image and packetized audio–were largely absent during test calls. According to Skype, that’s thanks to a new back-end addition that sticks a finger in the air of network conditions. As available bandwidth drops, the bandwidth manager tries to salvage audio first.

What my demo call looked like on a Vista set-up.

In choppy conditions, it helps steady the video, too, by lowering the rate of frames per second and by compressing images more heavily. Your friend on the other end may become blocky and the image delayed, but faces should also break up less than in previous versions.

Other new features include abuse reporting if you receive an invite from an unauthorized Skyper, and a light stub installer that pulls down the rest of the application.

Skype, it seems, has also been pulled into a toolbar partnership. Now when you install it, you’ll see that an optional toolbar that comes bundled with Skype 4.0. The free Browser Highlighter includes the ‘Compare on eBay’ tool for Firefox and Internet Explorer. Considering that eBay owns Skype, it’s not a surprising addition, but one I’ll nonetheless pass on every time.

What’s missing

There are two skins in version 4.0, the default light gray and blue combo called Skype ‘Chrome,’ and the classic hue. Skype hinted at more skin support in later versions coming out this year. There aren’t plans at the moment to support third-party skins, but customization, I’ve been assured, will get more attention.

Along these lines are absent customizations that had not been making beta testers happy. If you’ve been holding your breath for greater IM treatment in this release, or birthday reminders, you might breathe again until the next launch.

Those of you shouting about the cessation of public chats will be glad to know that Skype 4.0 for Windows will support those you already have, but it will keep you from adding new ones. Skype representatives told us they’re still playing around with ideas of how to become more Web-oriented. It could as easily look like a reshaped version of chats as it could go in a different direction.

That brings us to Skypecasts, another source of some users’ lamentations. Skypecasts was pulled last September because it just couldn’t grab the hoped-for attention. A similar(-ish) feature will probably be rolled into whatever public chats becomes in future releases.

For now, Skype has retreated to its bread-and-butter position of providing good, clean voice, video, and text chatting. If worldwide Windows users notice consistently improved audio and video quality, that’s not a bad place to be.