Can you really fit 5.1 channels into two and then get the 5.1 back out again without glitches? And does Neural processing have any impact on the sound - especially when you listen to the surround mixes in stereo? Inquiring minds wanted to know.
I started my audition not with an HD Surround receiver but with my trusty Roady 2, a stereo XM receiver. If Neural processing affected the sound quality through a legacy receiver, XM's 6.5 million subscribers would not be amused.
I went to XM Pops and Fine Tuning. The latter is very eclectic, providing a good test bed. For example, I listened to Al Di Meola's "Señor Mouse" from Flesh on Flesh, Steve Howe's "Meridian Strings" from Skyline, and Sting's "Desert Rose" from Brand New Day because I've heard these songs many times in both stereo and surround, and I know exactly what they sound like.
The Neural Surround processing didn't seem to introduce significant artifacts into stereo playback, and stereo reproduction of what were originally surround mixes sounded natural. Since it takes a while to get used to hearing unfamiliar artifacts, I'll reserve my final judgment for a few months. But after a week of listening, I was content that the added surround content didn't significantly degrade stereo playback.
Next, I turned to an Onkyo TX-SR504 receiver ($300), which is XM-ready and equipped with Neural Surround. After plugging an XM Connect-and-Play antenna into a port on the receiver's back panel, I zeroed in on XM Pops and Fine Tuning, listening to surround broadcasts of Mike Oldfield's "Finale" from Tubular Bells 2003, Mussorgsky's Night on Bald Mountain, and the title track from Dire Straits' Brothers in Arms.
Spatially, HD Surround isn't as good as the original mixes - not surprising, given the relatively low bit rates that XM broadcasts with. And on some songs, the fidelity of the surround channels was significantly inferior to that of the front channels, with artifacts that weren't always masked by the front channels. On many songs, though, both the front and surround channels sounded quite good. Either way, surround creates a sense of envelopment that stereo just can't provide. Overall, on most songs, I was happy with XM HD Surround.
There was one serious bug with the three HD Surround receivers I tried - the Onkyo, the Pioneer VSX-816 ($299), and the Yamaha RX-V559 ($450). The fidelity was seriously degraded whenever I listened to regular stereo channels in Neural mode, so I had to turn Neural on and off for surround playback. (XM says HD allows for automatic detection. It's up to receiver makers to employ it to turn the decoder on and off.)
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