MP3 and 3D Audio, Perfect Together.

By Richard Menta- 8/22/99

Do you know why you have two ears? For the same reason you have two eyes, depth perception. Humans see and hear in stereo, each eye or ear processing the same information at a slightly different angle and combining them to define distance and location. This improves fidelity and that is why our audio systems have two speakers instead of one - better sound.

Still, home stereo isn't spatial. While you can perceive sound from left to right, all the sound is in the front and you do not sense sounds from fore to aft. If you could add that ability, sound quality would increase significantly. Since most MP3 listeners rely on the modest speakers that came with their computers, they, in particular, would benefit greatly from such an improvement. Enter 3D audio.


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3D audio has been marketed to home PC's for years, but more as a gimmick with limited purpose. With the growth of MP3 music and the knowledge that computer systems are subbing for home audio systems, several companies are attempting to leverage this technology for this new music audience. The good news is they succeed in improving sound quality for the growing PC audiophile market.

So how does 3D audio work?

Using a technique similar to that employed in 3D movies - the speakers target each ear individually the way colored 3D glasses target each eye - 3D audio promises to deliver 360 directional sound. It does this by mimicking how the ears distingish sound to create that fore to aft perception.

Let us look at how humans can localize sound using only two ears.

A sound generated in space creates a sound wave that reaches the ears of the listener. If the sound is to the left, it reaches the listener's left ear a split second before the right ear, thus creating a slight delay between when both ears receive the signal. In addition, the sound to the right ear will be slightly altered because the head itself blocks or "shadows" some of the sound reaching it.

Both ear signals are then subjected to a complicated filtering process where the brain uses these delays and shadows to estimate the location of the sound source. 3D audio works by copying these delays and shadows - the left ear signals coming from the left speaker, the right ear signal from the right speaker - and fooling the brain into believing sounds are coming from the side or even the rear of the listener.

In theory, and under ideal conditions, the listener could hear a cello to their right, the violins to their left, the percussion section behind them, and the singer in front of them, and all with only two speakers.

Limitations

There are limitations to this technology. First, the listener must sit or stand directly between the two speakers. While this is not how most people listen to their home stereo systems, it is exactly the way we listen to our PC systems which is why products like WaveSurround and QSound, both shareware, are trying to leverage the technology for computers.

Second, there is the issue of crosstalk. This is when the right ear picks up some of the signal coming from the left speaker and vice versa, confusing the brain and diminishing the intended effect. (headphones are the ideal medium for 3D sound because they isolate each individual ear to its respected source). To reduce this effect, a digital filter called a crosstalk canceller is employed.

The third, and greatest limitation, is that human heads and ears are all different sizes and shapes. This means each individual has a different set of directional cues which limit the full effect that can be achieved.

WaveSurround, by Human Machine Interfaces, is a plug-in for WinAmp and works around these limitations very well. To start, the software doesn't try to separate individual instruments, a process that would require programming within the original music files themselves. Instead they do something clever.

Ask any audiophile and they will tell you the optimal placement for speakers are usually several feet apart. Computer speakers, on the other hand, are often only separated by several inches, the width of a monitor.

In effect, the result is not much different from that of just having a single speaker in front, and much of the advantages of stereo are lost.

What if technology could simulate speaker placement?

Virtual Speaker Placement.

Using 3D audio, WaveSurround allows the listener to adjust the sound in a way that virtually move the speakers. This is a lot less demanding technically than attempting to separate instruments, and is more practical to the limitations of the theory. The software uses a simple interface, with a graphic of a head surrounded by two moveable speakers and a slide bar.

I sit down - centered between my modest computer speakers - open WinAmp and activate the WaveSurround plug-in. Frank Sinatra's Just the Way You Look Tonight is our test song.

I slide the bar to the top, placing the graphic display of the speakers all the way in front. The sound eminating from my real speakers sound almost the same, though Frank's vocal does come over slightly stronger from the center.

I move the graphic speakers near 90 degrees, to the side and just slightly in front of the ears of the head. This simulates speakers that are maybe four or five feet apart and whose fore/aft position is closer to optimal. I close my eyes.

After a half second delay, the 3D audio kicks in and a surprisingly significant change occurs. I truly got the sensation that the my real speakers had indeed moved. This neat trick of audio ventriloquism was quite successful in its simulation of a more ideal speaker placement. Most important, the quality of the sound improved.

Assuming I don't just have the ideal ears for this technology, WaveSurround did a wonderful job at compensating for the unique directional cues of the individual. The music fidelity improved by a good margin, more than I expected frankly, and I felt the difference. Of course, I lose the effect anytime I stand up or move my chair away from the center of my speakers, but my normal clattering on the keyboards usually keeps me well within the physical area I need to be for WaveSurround to do its job. The end result was impressive.

Recommendations:

Because it is free, there is no excuse for WaveSurround plug-in not residing on all WinAmp users machines. The improvement in sound fidelity is significant and while it does have its limitations to where the listener must park themselves, it is well within reason, especially for those of us who are chained to our PC's and simply like a little good music in the background while we toil away. If that describes you, go to Human Machine Interfaces site and download it now. Your ears will thank you.

Copyright 1999 MP3 Newswire. All rights reserved.

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