Why does XM radio sound so bad?

[Jeff]

I have recently purchased a Benchmark DAC1. The purpose of this purchase was two fold. The first to provide better resolution for 2 channel enjoyment via my CD player.

The second, was much better resolution of XM radio via my DirectTV satellite. Listening to XM radio by using the dac's in my receiver or those found in the DirectTV reciever isn't very satifying. I had hoped the Benchmark
would provide near the playback quality as my cd player.

Connecting the DAC1 via the optical out from my dish receiver, the conclusion was immediate. Something is just not right in the world of XM radio. MY pre/pro tells me I'm receiving a 24 bit signal,bitrate of 2304 kbps at 48khz. This is much more information than my cd player provides, yet my cd player make XM seem like a pooly compressed MP3.

Any thoughts?

Jeff

[Kevin D]

Xm is poorly compressed Mp3! They have to fit a lot of channels into a small bandwidth and the results are obvious. I'm sure dish and directv could offer better sound then the normal tuners, but it seems they get the signal after it's been processed.

Kevin D.

[jim777]

XM radio (and Sirius) is very low bitrate audio, somewhere around a 32-48kbps (can't know for 100% sure, they won't say!!). At least it's enhanced AAC+, not MP3. Ah, and there is also reason to believe the audio is modified to compress more and sound "better". Both services want to maximize the number of channels, not the quality..

[Jeff]

Jim, that's interesting your understanding of the bitrate is 32-48 kbps. When I play it on my Sony, it tells me it's 2,304 kbps. This is what's confusing. When you look at just the numbers I'm receiving, one would think I'm receiving a high resolution XM feed.

I'm sure there are more pre/pros out there which tell the bit rate as well as the kbps. Perhaps my Sony is wrong. Although on dvd's and cd's it appears to be providing the correct information.

I can certainly understand them wanting to fit as many channels into their service as possible.

Thanks, Jeff

[jim777]

That must be like a 128kbps stereo 44.1kHz MP3 that, once decoded, is 2*16*44100 = 1,411,200bps... The resolution of the decoded bitstream and the bitstream itself don't have the same bitrate (otherwise it wouldn't be called compression).

BTW most cable companies will then call that CD quality, my cable company says that it's 1.4Mbps video stream is DVD quality..

[Jeff]

That’s technical jargon isn’t it? Hmmmm….

I will default to your wisdom.

Do you think what Kevin D said mades sence? I'm thinking it does. It's likely already compressed before it gets to DirectTV. I have well over 400 stations from Directtv. Correct me if I'm wrong, but doesn't video take up more space than audio. Given the number of channels directtv has, you would think it's not a space problem.

Here's another idea. Do you think there was an agreement with the record companies not to produce a cd quality stream? This would prevent bootleggers from producing and marketing music obtained by XM or Serrus.

Jeff

[jim777]

I use Illico (digital cable) and they compress audio too much even if audio bitrate is small compared to video. Old 192kbps MP2 (MPEG-1 layer II, not even MP3!) on average.

I guess DirectTV does something similar.

This gives you an idea of channel bitrates. To give you an idea, a DVD is 8Mbps max.

http://illico2.tripod.com/NumMtl200611.html

So much for "DVD quality"...

[Kevin P]

Jim, that's interesting your understanding of the bitrate is 32-48 kbps. When I play it on my Sony, it tells me it's 2,304 kbps. This is what's confusing. When you look at just the numbers I'm receiving, one would think I'm receiving a high resolution XM feed.

The "2,304 kbps" your receiver reports is after the bitstream is decompressed back into a raw PCM bitstream. What actually comes off the satellite is 32-48 kbps. The satellite box decodes (and decompresses) this before passing it along. But of course, the damage has been done, and that 2,304 kbps signal sounds like garbage.

It's kind of like downsizing a JPEG from 2048x1536 to 320x240, and then upsizing back to 2048x1536. The end result will look nothing like the original.

[Kevin D]

Just because I'm bored. Here's Kevin's example:

1: Is the original CD
2: is the CD in the XM stream
3: Is the CD back to CD 'quality' after the tuner, DAC, etc..

[Ovation]

Very effective visual aid.

[Jeff]

Thanks Kevin. A picture is worth a thousand words.

I assume this is your HT set up.

[Kevin D]

Thanks Kevin. A picture is worth a thousand words.

I assume this is your HT set up.

hehe... Not quite.. That's a customer's house. I think the wood in that room costs more then my system..


Kevin D.

[Chris D]

Wow, Kevin, I like that room!

On the original topic, yes, I'm disappointed with satellite radio. Having a digital source, it has the capability of being high-def and/or multichannel, but doesn't? Why? Because J6P wants 5,000 channels of music, not high-quality sound!

[PewterTA]

/rant_on

A lot of it has to do with .mp3 and even more importantly the introduction of the mainstream "iPod."

Most people want quantity over quality. ..and in some ways, I can agree to that way of thinking. If I'm not sitting and critically listening to things an iTunes file sounds good to me (along with the music channels on my digital cable) as long as I'm doing something else, reading, cleaning, working, etc. So what do I want, as many different songs to listen to ask I can get. However, if I am paying for something to listen to/download and it's going to cost me equal amounts to buying a CD, then I want the quality of the CD!! Course I'd really like better than CD quality since most single songs uncompressed are over 1 or 2GB...but I'm a realist on that part...

Anyways,

This is where people need to get educated though. We shouldn't have to stand for quality loss! To me, none of these "digitally broadcast music things" should be anything less than 256Kb compression. You should get as close to CD quality as you can (yes 320Kb ideally) and it still takes very little space to transmit. Yet people don't care that they are actually getting ripped off by the entertainment industry all for the sake of convience...

I don't know about you, but it p(*&$es me off that iTunes is going to start selling "HD" quality files...all the while it's only at 256/320KB. I say this is pathetic, there's nothing "HD" about the whole d&$#ed thing!

Course maybe that's why I don't pay for iTunes and am happy that I don't have to pay extra for the digital music channels. ...and you'll never see me with xm/sirius. I won't pay for poor quality.

/rant_off

[Ovation]

If I get sat radio, it will only be for my car and it will be for sports and news channels (NPR and the like). The music will be a bonus and, as far as I'm concerned, in the car, SQ is an iffy proposition if it isn't Lexus-quiet in there (and in my 10 year old Pathfinder, it ain't all that quiet).

Just my 2 cents