So...wondering about the Polk XM tuner

tugboat · October 2005

Okay, some will remember the discussion on MP3s and how they are not up to SDA standards. I agree with this, but was just wondering how the XM tuner from Polk is viewed. Now if I'm wrong, please correct me. Isn't XM just another form of MP3? From what I've been able to learn, XM is a fixed bit rate and Sirius is a variable bit rate digital transmission of compressed music, etc. What I haven't been able to find is the type and extent of compression used by both. I'm sure the bit rate is on the low side as listening to XM with my Alpine unit in my truck lacks depth and detail and don't get me started on bass. Okay, so if I'm not wrong about the loss of detail from compression, then how can the XM tuner from Polk stand its ground? They boast having Burr-Brown DACs, etc. My Denon 5803A has Burr-Brown DACS, but no matter how good they are, they can't convert crap into gold. Am I missing something here, or am I on the mark?

The only thing I do know is that XM on my 1.2TLs sounds "okay," but the Sirius channels on Dish Network sound better (even if it's nothing to write home about). I lend that to the variable bit rate over the fixed for XM.

Thanks!

danger boy · October 2005

I don't know about bit rates and MP3's etc. all i know is that i highly doubt anything can compare to having Redbook CD in your high end CD player. it's the least processed way to hear good sound. Even with the best satellite signal and XM or Sirius tuner.. it's still processed and or compressed thru the signal from whereever it originated.

That's why i have little interest in satellite music.

FYI, Polk considers their XRt-12 XM tuner to be a "reference" tuner.

jdhdiggs · October 2005

THe Polk Tuner does offer better sound than the other units. Check in the electronics section for more details on all the specifics of XM. I have no issues with it's sound quality. Is it CD? Nope, but its a lot closer than most MP3's I've ever heard.

ohskigod · October 2005

I dont know the technology specs and the numbers, I concur with james though, its not CD quality, but I can say with absolute certainty that the Polk tuner smokes the bejesus out of the Delphi Skyfi I was using through my theater system.
I use it for an easy music source during parties and whatnot, since I dont have a multi CD player. Also, I'm a huge Opie and Anthony fan.

tugboat · October 2005

Was/am certain that satellite radio is nowhere near CD quality. I only have it in my truck for long drives, etc. I can see the Polk XM tuner be reference quality if the data stream was uncompressed/unaltered audio from a CD or master. Since it's not, the Polk unit can walk all over the competition with quality DACs, but it's reign ends there. I'm assuming (again) that any unit (mobile or not) with a digital out would sound as good or better being decoded by the higher end Burr-Brown DACs in my Denon.

So, basically, the XM unit from polk is making sure you hear the best possible audio even if that isn't much.

madmax · October 2005

tugboat wrote:

So, basically, the XM unit from polk is making sure you hear the best possible audio even if that isn't much.

It really isn't that bad of a sound. It doesn't have any obvious defects and artifacts like I've heard from mp3's. The bass is large and open. It is a step down from CD but not even close to the poor level of mp3's. I've compared it to my Sony XM and it beats the pants off of it and the Sony is better than most of the current XM's.
madmax

nadams · October 2005

The XM unit from Polk uses better components, because it doesn't have to take size into consideration. When you look at the components inside, you can see where they wouldn't be able to fit inside a Roady2 or Skyfi tuner.

Yes, there's a lot of empty space in the case, but they wanted it to look like the rest of your components in the rack...

madmax · October 2005

The grey box towards the right is the XM module. That thing wouldn't even fit in my sony... The reception is better too.
madmax

jcaut · October 2005

Let me start out by saying that I have XM in my GM vehicle, but it plays through the factory Bose POS stereo. Needless to say, it doesn't sound good on any source, but CD's still sound WAY better than anything I've ever heard on XM. I attribute that mostly to the quality of the hardware involved, (in other words the CD section probably uses better parts than the XM tuner) but it's bound to have something to do with XM being compressed as well.

I haven't heard the Polk tuner, but I'm sure it's capable of squeezing almost all the sound quality you can get out of the XM signal. Polk feels that XM is here to stay and they want to provide a high-quality component with which to receive it. They consider it a "reference" XM tuner because it's way better than any other XM tuners currently available. It's still limited by the quality of the compression scheme, however.

I read somewhere --I can't remember the source and I have no idea if it was correct-- that XM uses a lossy compression similar to mp3, at a constant bitrate of 96kbps. Sirius was said to use a variable bitrate scheme that averages about 84kbps. As I said, I don't know if that's true or not, but assuming that it is, I can't really see how it would be possible for either format to sound better than, say, a well encoded mp3 at 160kbps or higher. While there are some codecs that do better than mp3 at low bitrates, 96 is awfully low.

And speaking of mp3's: While it's true that there are tons of really horrible-sounding mp3's floating around "out there", the mp3's that I make myself, for my own use, don't sound bad at all. I encode with LAME 3.90 with the 'preset-standard', which is high-quality, variable bitrate scheme that produces files with an average bitrate near 224kbps. I'm not arguing that they're CD quality and I don't use them for serious listening, but when played back on good equipment, I'm hard pressed to tell them from the CD.

Jason

heiney9 · October 2005

Both satellite radio and digital cable music is compressed in very much the same manner as MP3's. The band width just isn't there yet for full blown cd resolution. Or if it is they aren't bothering to transmit full cd quality. So to answer your question yes XM is very much like MP3. However the better the receiver the better the sound. From what I've heard the Polk tuner is among the better ones. I listen to digital cable music channels as background music sometimes and it's not too bad.

H9

heiney9 · October 2005

jcaut wrote:

I read somewhere --I can't remember the source and I have no idea if it was correct-- that XM uses a lossy compression similar to mp3, at a constant bitrate of 96kbps. Sirius was said to use a variable bitrate scheme that averages about 84kbps. As I said, I don't know if that's true or not, but assuming that it is, I can't really see how it would be possible for either format to sound better than, say, a well encoded mp3 at 160kbps or higher. While there are some codecs that do better than mp3 at low bitrates, 96 is awfully low.

Jason

96 kbps is pretty bad if that's what they are using. A normal .cda or .wav file (cd quality) is 1411 kbps just to give an idea of the difference. I do listen to MP3's on a portable and I have some on my computer for the computer rig and I always encode @ 320 kbps. This is adequate to enjoy the music but certainly could never be mistaken for cd quality.

H9

So...wondering about the Polk XM tuner

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