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Vista audio enhancements revealed

9/7/2006 7:57:50 AM, by Jeremy Reimer



Much of the hype surrounding Windows Vista has been concerned with its graphics: the new, DirectX-powered Windows Presentation Foundation (WPF) graphics engine, and the translucent Aero Glass visual themes laid on top of it. Visuals are perhaps the easiest feature to sell a new operating system with, and Vista has pulled out all the stops in this area. However, until now very little attention has been paid to the audio improvements in Windows Vista. Let's take a look!
Loudness equalization

One annoying feature of watching broadcast television that everyone is familiar with is the fact that different channels have their volume tuned to different levels, and commercials have volumes louder than any of the programs. This leads to constant fine-tuning of the volume control in order to achieve an acceptable sound balance.

Some high-definition televisions already come with volume-leveling controls built-in, but these only work if you are using the television's speakers—most people with HDTVs will be using their sound systems to listen to the audio feed instead. Windows Vista will maintain a relatively constant perceived volume while playing different audio files or sources. Some applications—such as Apple's iTunes—already implement volume-leveling technology, but that must be applied to a single music file at a time. Vista's system works in real-time, analyzing both long-term and short-term fluctuations in sound volume in order to apply a constant equalization. This feature can be turned off if desired in the Control Panel.

Loudness equalization in Windows Vista

Another neat feature in Vista is that, for the first time, different audio sources can be manually adjusted for different volume levels. This is extremely handy if, for example, one wants to watch a recorded episode of Battlestar Galactica on Windows Media Center while simultaneously listening to the free audio commentary podcast by creator Ron Moore. Vista will allow one source to be turned down in volume while the other is cranked up.
Bass management

Many sound systems come with a large subwoofer speaker to play low frequencies that aren't handled very well by the smaller main speakers. For those without a subwoofer, Vista adds a utility called "Reverse Bass Management," where low frequency and bass sounds are channeled from the small speakers to the largest speakers available, such as the midrange Front Left and Front Right speakers. The frequency to trigger this crossover can be adjusted manually, and Vista will also make adjustments based on the size of the room (several options are available in the control panel dialog box).
Speaker fill

Speaker fill is a technique that is used when there are more speakers available than channels in the source music. In other words, if you have a music file that was recorded in stereo with only two channels, Speaker fill will synthesize additional channels and direct them to the appropriate speakers. It works by manipulating the channel sound in subtle ways—such as adding small delays or applying a filter—and then channeling the appropriate frequency levels to the appropriate speakers.
Room correction

Room correction is a feature found in extremely high-end audio hardware, which finds a "sweet spot" for the listener in any particular room. It performs this magic by using a microphone to calibrate all areas of a room, including adding a first-reflection cancellation filter if one or more of the speakers are near a flat surface. The microphone is placed in the location where the user would like to sit, and then a calibration wizard is run to figure out the distance, frequency, response, and overall gain of each loudspeaker in the sound system. Optionally, if a high-quality microphone is used, the system will add correction for relative frequency response differences coming from each speaker. According to Microsoft, room correction takes up less than five percent of CPU time on a 3 GHz processor.

Speaker phantoming

Speaker phantoming is a technique that will automatically detect if a particular speaker is turned off or not functioning, and compensate by splitting the sound from that speaker and distributing it to adjacent speakers. A typical example would be moving sound data from a missing center speaker to the left and right channels.
Surround headphones and bass boost for laptops

Many people prefer to watch movies or listen to music on the go, and a laptop with headphones is one way of doing just that. Vista adds virtualized surround sound for headphones, using a technology called Headphone Related Transfer Function (HRTF). HRTF uses digital signal processing to synthesize sounds that mimic the ear's natural response to sounds in a real-world environment, such as the tiny delay that sound takes getting from one ear to another. This allows for sounds to appear to move around in a virtual three-dimensional space while using headphones.
Microphone arrays

This last feature is rather esoteric, and requires specific hardware to support it. Basically it allows multiple microphones to be placed in a laptop, LCD display, or Tablet PC, with the goal of improved speech recognition. The microphones can be arranged in any pattern, but an evenly-spaced single line fits well with the hardware. The extra microphones allow for improved acoustic echo cancellation and noise suppression, making it easier for speech recognition software to hear the user accurately, as well as making voice communications more clear.

Any one of these technologies by itself is interesting, but when bundled together in a complete package, it represents a significant investment by Microsoft in enhancing the audio capabilities of the operating system. A new audio engine architecture has been built for Vista, with most of the advanced features living in user space, with only the audio driver itself still in kernel mode. This should help with stability and keep the system going even if one of the advanced features runs into a problem or a bug.

Microsoft is clearly serious about the battle for the living room, and with the inclusion of these new features makes a strong case for the inclusion of Windows Media Center as part of a high-end audio and video setup. Audiophiles should find plenty to rejoice about!

For more information, we point you to product manager Nick White's report on Microsoft's TechNet blog.