anyone know if XM is broadcasting any channels in 5.1-channel surround sound; I just bought a new A/V receiver (XM ready) and new 5.1 speakers, and am wondering if there are any XM channels that are HD 5.1 channel surround?

Before the changes XM Pops and Fine Tuning were in 5.1 surround sound.

Now just SiriusXM Pops in 5.1/HD...

In the nitpicking department, Sirius' version of "5.1" was really just a matrixed surround. You could get the same results on any (stereo) channel by turning on your Pro Logic decoder.

There is a big difference between real 5.1 (like on DVDs) and fake surround.

Why on earth would you want 5.1 radio? So SQ can decrease even more as we give 6 channels of audio to every station? :p

Half the stations on satellite radio (sports, talk, news...) aren't even worthy of half the bandwidth they are currently given.. Sirius already sounds like an AM radio, let's not make it sound like an AM radio from the sixties.

In the nitpicking department, Sirius' version of "5.1" was really just a matrixed surround. You could get the same results on any (stereo) channel by turning on your Pro Logic decoder. There is a big difference between real 5.1 (like on DVDs) and fake surround. Bzzzz. Matrixed surround is not fake. Dolby Pro Logic uses time-domain phasing to create 5 distinct and separate channels, and so too do digital codecs like PAC, MP3, and AAC. There's nothing "fake" about it.

Bzzzz. Matrixed surround is not fake. Dolby Pro Logic uses time-domain phasing to create 5 distinct and separate channels, and so too do digital codecs like PAC, MP3, and AAC. There's nothing "fake" about it.
"5.1" implies discrete, at least to me (and most other people who know the difference.) More nitpicking, but I guess I mis-spoke before. "Surround" could be matrixed, but "5.1" cannot.

"Time-domain phasing"? What is that? It sounds redundant.

Anything that takes two channels (stereo) and derives 5.1 is fake, or not discrete.

As far as I know, there is no discrete 5.1-channel coding on sat radio.

"5.1" implies discrete, at least to me Dolby's matrixed surround *is* discrete. Each channel is kept separate from the other channels. It is not a case of 2 channels becoming 5 (what you call fake). Dolby Pro Logic is a case of 5 separate sounds recorded into 5 separate channels. Not fake. There is a big difference between real 5.1 (like on DVDs) and fake surround. Well if you don't consider Pro Logic discrete, then you should not consider DVD Audio to be "discrete" either. All the channels commingle into a single bitstream. ONE. Not five.

And of course DVDs use compression algorithms, where perceptive coding thinks 5 channels "sound like two to humans", and dumps the other three to save space. The 3rd, 4th, and 5th channels are only recorded as needed, as "difference signals" to the original two. They do not exist discretely.

In some cases even the stereo is not discrete stereo, but a single left channel plus a "difference" to derive the right from the left.

Dolby's matrixed surround *is* discrete.

Ah... NOPE! No it isn't. (At the risk of starting a Monty Python parody...)

Each channel is kept separate from the other channels. It is not a case of 2 channels becoming 5 (what you call fake). Dolby Pro Logic is a case of 5 separate sounds recorded into 5 separate channels. Not fake.

Again, NOPE! Dolby Pro Logic is a decoding scheme that derives surround from stereo by making a few assumptions. Put simply, if something is the same in the left and right channels (and in phase) it will be directed to the center channel output of the decoder. If the signal is the same, but out of phase, it gets directed to the surround output. Left stays left and right stays right.

Pro logic 2 can be a bit more creative in determining whether things are in phase or not, and can create a left surround and right surround. This gets closer to the idea of "5.1" (or at least the "5" part.)

Pro logic encoders exist, but you don't have them at home. (OK, that's not completely true, but it's good enough for now.)

Well if you don't consider Pro Logic discrete, then you should not consider DVD Audio to be "discrete" either. All the channels commingle into a single bitstream. ONE. Not five.

NOPE! Pro logic works on audio signals, not a coded digital bitstream. Maybe you are confusing this with Dolby Digital, which is a bitsream, and is discrete.

DVD-Audio is discrete. Even more, it's numerically lossless

And of course DVDs use compression algorithms, where perceptive coding thinks 5 channels "sound like two to humans", and dumps the other three to save space. The 3rd, 4th, and 5th channels are only recorded as needed, as "difference signals" to the original two. They do not exist discretely.

I take it you do not design perceptual (not perceptive) encoders. True, they only code what the human ear can hear, but it's not because it "sounds like two," and the other channels are not sent as "difference signals."

In some cases even the stereo is not discrete stereo, but a single left channel plus a "difference" to derive the right from the left.

NOPE! (Strike three, you're out!) If stereo is being delivered as two channels, it could be discrete, but not always. Your red and white RCA connections are discrete. Your FM radio isn't. But again, it isn't a left channel and a "difference" to derive the right. It's actually a sum of left and right in one channel, and the difference between left and right on another.

High school algebra will show you that

(L+R)+(L-R)=2L and
(L+R)-(L-R)=2R

That's how you get L and R through a matrix, and it works perfectly. The Pro Logic system isn't completely reversible, so you get artifacts.