Yamaha @PET RP-U100 personal receiver:
Page 2 A wide variety of algorithms are employed in the virtual audio world, from game-oriented "positional" 3D effects in soundcards to bass enhancement, mono-to-stereo, stereo-to-"virtual surround," and true 3D audio, to name a few. Most of these methods include manipulation of and trading between interaural time delays (ITDs) and interaural intensity differences (IIDs) of sound stimuli arriving at the ears from multiple directions. These values are then combined with techniques such as crosstalk cancellation, equalization, and bass-enhancement methods to achieve the desired illusion.

ITD is the difference in the time of arrival for a given sound at each ear, and IID reflects amplitude differences due to the shading effects of the head. (Sound coming from one side will be attenuated by the head.) Both processes are basic components of the head-related transfer function (HRTF), which models the directional and timbral impacts that the shapes of one's ears, head, and torso have on sound arriving at each ear from many angles.

Though HRTFs vary from person to person, we all have enough in common; algorithms properly applied and fine-tuned can profoundly affect the illusion of a three-dimensional soundscape. Still a ways off, however, are commercially viable products—matched with more computationally efficient and elegant algorithms—with enough DSP horsepower to adapt, transparently and without artifacts, multiple HRTF curves in real-time to account for head and source movements within a listening room of normal size. Hence, processing that includes adjustable HRTF filters is most practical for headphone use or nearfield listening environments, where the variables of room acoustics and speaker-to-listener distances are better defined—such as in a computer-based audio system. In addition, while most virtual 3D techniques are intended for stereo speakers, some methods aim to improve multichannel systems as well.

Inside the Yamaha
The Yamaha receiver is constructed on just four main circuit modules. A large, vertical printed circuit board on the right-hand side carries the output amplifier, this based on a complementary pair of what appear to be bipolar transistors for each channel fastened to a folded aluminum heatsink with quite a large surface area. On the left rear, a large shielded module contains all the digital circuitry, with the tuner circuit on a small board behind it. A board behind the front panel carries all the control circuitry.

Installation
The RP-U100 is truly plug'n'play. When I connected the supplied USB cable to the receiver, my PC informed me that it had found new hardware and was installing the driver software, prompting me to insert the Windows 98 CD-ROM as required. I installed the control and GUI programs from Yamaha's supplied CD-ROM. Once the software is installed, clicking on the Multimedia button in the W98 control panel allows you to tell the RP-U100 what kind of speakers you're using and to set the Yamaha's USB as the default audio port. Sometimes when I booted up the computer there was a glitch, the PC telling me it couldn't find the RP-U100. Reinstalling the drivers fixed this occasional problem, but it left me feeling a little apprehensive.

The RP-U100's GUI provides intuitive control over the receiver's many signal-processing functions.

The GUI is intuitive to use: Click on the facsimiles of the front-panel buttons to operate them. One peculiarity: Click'n'dragging on the image of the volume control allowed me to set a maximum level of only "25," which is the unity gain setting. A safety feature?

Sound quality
I like to listen to our local NPR station in the office, so I hooked up the Yamaha's tuner section to a simple T-aerial fastened to my office window. (You need to use a 300/75 balun adapter for this, as the RP-U100 has only a 75 ohm unbalanced FM input.) Audio quality was fine; only with the weakest stations did I suffer from birdies or hiss.

Fed digital audio from an external CD transport, the Yamaha put out surprisingly robust sound. Despite its modest footprint, this is no wimpy, sonically compromised piece of kit. Obviously, with speakers on the far ends of my desk, I don't need hundreds of watts. But I had no problem rocking out to levels that forced my fellow office denizens to shut their doors—and mine. The sound was also sweet in the highs, though perhaps a little laid-back in the midrange.

Driving the receiver's digital input with the S/PDIF data output of my computer soundcard (a CardD Deluxe from Digital Audio Labs) and using WAV files of my own recordings as source material gave results no different from what I had experienced with CDs. MP3s downloaded from the Web, and those I'd made from CD tracks with the Fraunhofer encoder, also sounded excellent. However, changing to the USB connection for computer audio was disappointing: music acquired a slight grain. This was not a problem with computer games; the lushly ambient Riven soundtrack came over just fine, and benefited from the Yamaha's soundfield processing. Treating W98's sound messages with the Church algorithm was also a satisfying, if unnecessary, experience.