Audio Processing in Vista Explained
Some of you know about me and our activities in audio/video compression and HD optical formats such as HD DVD. But probably don’t know about other types of signal processing that my team does at Microsoft. To remedy that , here is high level description of audio processing which is included in Windows Vista.
Some of you know about expensive room correction hardware which in some cases, costs as much as $10,000. Well, in Vista, we have a perceptually tuned version of room correction. Because we don't expect everyone to own an instrumentation microphone, we have designed it so that you can use a cheap cardioid or omnidirectional microphone costing a few dollars to do an excellent job. IF you have a more expensive microphone, you can calibrate your room very accurately. All of this is implemented in in-box Vista software, using less than 5% on 3GHz CPU. Our room correction will equalize frequency response, time delay, and gain between all of your main channels, as well as build a first-reflection-cancellation filter if one or more of your speakers are near a reflective surface. If you do have a high-quality microphone, the room correction system will also flatten the overall frequency response and adjust the subwoofer delay accordingly. All of our adjustments are done as to capture the most obvious problems from the point of view of human hearing, allowing us to do a very effective job with a few machine cycles.
Beyond advanced processing like room correction, we have also added fully configurable Bass Management, Loudness Equalization, Headphone Virtualization for private headphone listening, and channel control tools to fill speakers (for example 5.1) from stereo material, as well as build phantom channels when, for example, your listening setup has no center speaker. In addition, both Headphone Virtualization as well as bass boost are available for laptops, for headphone and laptop speaker use respectively.
For Bass Management, we have provided the tools to set up your system with all large (bass capable), Left and Right large, or no large speakers, with or without a subwoofer. For instance, if you have small speakers and a subwoofer, the bass from all channels will be routed to the subwoofer, and if you have some large speakers and no subwoofer, the subwoofer signal will be routed to the large speakers. We also handle the case where you have some large, some small speakers, and will route the bass accordingly. You can set the crossover point of your system to whatever the loudspeakers require.
In order to explain what Loudness Equalization does, we must first explain some terminology. In the Psychoacoustic Discipline, the term "Loudness" refers to the listener's evaluation of how loud a signal is, and the terms "intensity", "sound pressure" and the like refer to the measured, external to the listener, mechanically determined level. Loudness and intensity are related, but not in a direct fashion, because the response of the outer, middle, and inner ear must be modeled in order to relate the two. Our Loudness Equalization does exactly that, and then equalizes not the intensity, but rather the loudness, of presented signals in order to avoid blasting the listener when switching, for instance, from an analog to a digital TV channel, or from an older, dynamic recording to a modern, highly compressed recording. While this does reduce the dynamic range of the sound, this is often desirable, both in a loud environment where the quiet parts of the music are hard to hear, and in a quiet environment where you want to avoid blasting others with the loud parts of the sound.
Many people (most, if some of my observations on airplanes these days are typical) watch movies on laptops on airplane flights, in airports, at home, work, and so on. In order to provide the full movie experience, we have added Headphone Virtualization which uses Head Related Transfer Functions (which are basically the frequency responses of your head for sound arriving from different directions) to simulate sound arriving not only from the left and right headphone, but rather external to the head, and from front, center, side, and back. In addition we provide artificial reverberation, so that you can chose your desired listening environment, from small to large room. Of course, we also provide this processing on desktop machines so that you can enjoy 5.1, 7.1, and HDTV audio in your headphones on your desktop as well. I suppose I should mention that we also provide a mid-bass boost option for laptop audio, for when you are using those small laptop speakers.
We have added the ability to control the speaker configuration in a very flexible fashion. In addition to the standard configurations of 2.0, 5.1 (with either surround or rear speakers), and 7.1 (with both surround and rear speakers), we offer the ability to separately indicate the presence or absence of the subwoofer (.1) channel, and for the user to indicate that a specific set of speaker/speakers (say side, or rear, or center) is not actually connected. When we detect that a speaker(s) is missing, we will virtualize that channel(s) so that the information in the missing speakers is still presented to the listener in an engaging fashion. Likewise, when we detect that the source material has fewer channels than the listening setup, we provide the ability to "fill speakers" with signal that creates an experience that is more enveloping, and that has a stronger central image and wider listening area.
Finally, for those listeners who do not have multichannel output from their computer, or multichannel inputs into their A/V Receivers, we provide Virtual Surround, a matrixing technology also called LtRt, to provide input to A/V Receiver features that convert 2 Channel sound into multichannel sound inside the A/V Receiver.
All these audio system effects (also referred to as SysFx DSPs) are available on any HD-Audio and USB Audio-equipped computer that uses in-box class drivers. Third party audio drivers that do not use the in-box class drivers will either have similar effects of their own or will re-use the inbox SysFx audio DSPs and expose them through the Control Panel. In short, we provide the functionality offered by a high-end A/V Receiver in the basic Vista in-box software (installed automatically for USB and HD Audio), with performance and functionality that is comparable to the best A/V equipment on the market. If you want to read more on the new Vista™ Home Theatre functionality, please go to page 167, section 4.07 of the Windows Vista Product Guide on http://www.microsoft.com/downloads/...&DisplayLang=en for more information.
Anyway, please let me know what you think of these of features. This is the first time we have put all of this signal processing in an operating system and would be good to know if this is a direction we should continue.
Microsoft (HD DVD insider)
Ask me questions about HD DVD here
Windows Vista Audio processing here