Sorry if this is a redundant post, but I couldn't search for "XM"... string too short for search.

Is anyone else disappointed with the sound quality of XM radio? To me it sounds worse than an MP3. Does anyone know what compression technique they use? It seems like General Motors might be backing them. I wonder if they're using excess bandwidth from Direct TV (Hughes - GM subsidiary) or maybe OnStar (but I think that's cellular based.) My wife wants to activate it after our trial, but I don't think it's worth it since the sound stinks.

Is there another thread somewhere on this issue?

Anyone else have opinions on XM quality? Thanks...ed

 

I'm no audiophile... That being said I have been very happy with the sound quality of XM Radio. There is an obvious quality difference beween generations (ie. 70's vs. Top 20) but that in how they were originally recorded.

All in all, I'm satisfied. I love the variety.

Hope this helps!

 

My wife and I haven't noticed any problems! The sound quality in my opinion is far better than standard radio ....

We're not MP3 people, so I haven't done the compare / contrast to that medium yet.

For us, we activated the service to get the variety of different channels that are available for listening.

 

Some stations (The 70's) have significant compression while others don't. The reason is a mystery to me. My guess is that they are actually digitally broadcasting to the satellite by different channels some with more bandwidth than others thus some need compression more than others. In summary I don't believe the data transmission protocols are standarized among the different stations. The most compressed are FM quality while the uncompressed are CD quality.

 

Never had a problem with any of mine...I find most of the stations to be better than cd quality

 

I agree, the quality is much better than FM on most stations.

The problems I have is that the signal is easily blocked by trees (with or without foliage) over passes and when traveling accross suspension bridges, and when switching stations it takes up to 10 seconds or so for it to come in (sometimes longer), so it is not eash to scan stations at a quick clip like FM. It is almost back to the days of AM reception.

Anyone else notice this, or is it my antenna?

 

I've noticed the same issues with tuning and signal re-acquisition. I'm guessing that the signal actually returns quickly, but the radio has to get enough of the compressed signal before it can start decompressing it.

I guess I'm being overly critical of XM sound quality. I feel that, for a subscription service, I should get exceptional quality. I switched to satellite TV for better reception vs. cable. I guess I should compare XM to FM instead of comparing it to MP3.

 

Here's the XM Radio blurb on their compression technology.

http://www.xmradio.com/newsroom/scre...002_04_18.html

Mike

 

I read that post a while back. They say how great it is compared to other, similar compression technologies in use. However, they never reveal how much actual compression takes place or how the algorithm works. It's kind of like saying 'this car handles better than its competitor'... so vague that it's really meaningless.

 

I have the similar issue. In the city, my signals sometimes are blocked by buildings or trees. I will lose the XM for a couple of seconds, then back, then lose again. However, my XM never delays 10 seconds to pick up signals.

In Boston, sometimes I had the same problem last weekend. But, when traveling to the south(TN,KY,VA), I got pretty good reception there. XM radio seems to have problems to deliver the full coverage from their ground antenna and "Rock" & "Roll" over the sky.

Perhaps, in the summer time, the situation would get worse 'cause the trees are luxuriant.

 

I love XM. So many different stations to choose from. Great digital sound quality, songs I haven't heard in years, musicians who I love but had never heard on the radio before, excellent sports and news stations, amusing comedy stations, etc. etc.

If the technology improves over time, great. If not, its still an amazing medium which provides endless entertainment for $10 a month. I'm in my car at least three hours every day and I love it.

Sometimes the signal gets blocked by overpasses and trees, but its no big deal. No complaints here.

 

I had Xm in my prior vehicle and it is a great service. The sound is much better than FM and close enough to CD. The issue I've found is that it is very flat after listening to DVD-A titles in the TL. It's just a testament to how good the DVD-Audio system is.

 

I wouldn't expect much of that to be revealed. I've found a few web pages that say the bit rate is 64kbps.

Mike

 

I don't think it sounds as good as FM myself; the compression is very noticable. I'm enjoying the DVD-A capabilities of the TL more than anything else about the sound system.

Mike

 

All educated conjecture because the actual methods are XM's proprietary info, but this seems to be a pretty educated guess. Says the bit rate is 48kbps.

http://www.xmxp.com/viewtopic.php?p=47

Mike

 

My buddy had XM in his car for a while. This was when it first came on-line and he did have some issues with the quality. I'm not sure if it was the signal, or the fact that he had XM going through an FM modulator into his regular factory radio.

The volume level would differ pretty badly from station to station, and it did seem to take some time to tune into certain stations.

The actual sound quality wasn't too bad, but it wasn't exactly CD quality (again, this was going through an FM modulator).

 

XM is a "collection" of channels. Each individual channel can (and does) have it's own quality. The technology itself is on par with CD quality. It's just that the underlying platforms may not be up to snuff. What channels do you experience Poor quality on?

 

Compression - It is clear from listening that the compression and the bandwidth vary from station to station. This is done to maximize the number of channels they can broadcast in their defined RF frequency range. Clearly, talk shows do not need full bandwidth, but some music channels seem to be cut down also.

Channel acquisition - It takes a little time to change channels because there has to be enough signal acquired to fill the buffer memory before it can start playing.

Dropouts - The frequency is very high - around 2.3 or 2.5 GHz I think. It is very easy for signals at this frequency to be absorbed by trees or blocked by overpases. It is too bad that the buffer in our radios is not larger - then it could still keep playing during short RF dropouts.

All in all - I feel it is worth it for the variety and relative lack of commercials. It ceretainly sounds better for the most part than broadcast FM. This is too bad also - FM and even AM can sound fantastic, but the broadcasters won't let it.

 

Y'know, I never really pinned it down to specific channels. I listen to The Loft, FRED, Deep Tracks, Bluegrass Junction, XMU, Real Jazz, Watercolors, and a few others I can't recall right now. As I recall, the Jazz stations sound good, but the others are more "muddy".... for lack of a better word. Even though everything seems midrange heavy, lyrics don't seem to stand out like they should. Deep bass in a car with a solid subwoofer like the TL should be strong though it often seems non-existent... like they've rolled off everything below 150 hertz. I don't know... maybe I just expect too much.

 

Do you mean when listening on a table radio? XM is not even as good as a decent MP3 rip at 192 kbps let alone uncompressed .wav.

 

The worst sound quality I've heard on a "music" channel on XM is Disney Radio (115). It's barely better than the quality of the local AM broadcast of the same station.

Mike

 

What I don't like about XM radio, besides the 12 programmable presets Acura gives you, the rest of time you have to use the radio knob. I wish you could cycle thru all the XM channels with using the steering wheel controls.

 

That's the same way the FM (and I presume AM) works too; the steering wheel controls cycle through the presets. That's purely an ELS system thing, not an XM thing.

My preference is for the way it operates. The knobs fall easily enough to hand if I'm looking for something outside of my presets.

Mike

 

All digital audio compression techniques I've heard, including the mpeg's and XM's CT-aacPlus, sound bad at low bit-rate's. Just how bad depends on source material, bit-rate, and the listener. For example, at 192Kbs very few people can hear MP3 compression artifacts but at much lower rates it becomes obvious to almost everyone.

The 48Kbs XM bit-rate mentioned in the link posted earlier is quite low and it is not surprising that many people are bothered by XM compression artifacts. To my ears, complex sounds, such as string ensembles, often have a very unpleasant "phasey distortion" on XM. The distortion is similar to what I hear at low MP3 bit rates but pretty much disappears above about 92-128Kbps.

It is difficult to compare digital XM to analog FM because their distortion artifacts are completely different in cause and nature. If your car is parked in a good signal area with no multipath when tuned to a good FM station, the sound quality is much better to my ears than XM due to the lack of digital compression artifacts. In normal driving situations, however, multipath and varying signal quality will degrade FM considerably and to me, XM is generally superior overall.

In overall sound quality and distortion, I would rate the TL's sources as follows:

1. DVD-A
2. CD (mostly due to 2-channels vs 6)
3. XM
4. Tape (hiss, flutter, drop-outs)
5. FM (typical driving conditions)
6. AM

This does not factor in the convenience and variety of channels that XM offers, however. I just came back from a long trip through California, Nevada, Arizona, New Mexico, and back, and spent at least 90% of the time listening to XM, about 1% to DVD-A, 2% to CD's, maybe 0.1% to AM and the remainder listening to the engine.

 

Some of the information is available on XM's own web site. It is not broadcast from DirecTV satellites, or On-Star. On-Star is really a combination of a cellular phone and a GPS receiver.

On XM's own web site they show two geostationary satellites called 'rock' and 'roll.' This is in contrast to Sirius who I believe use a constellation of orbiting LEO (Low Earth Orbit) satellites in a pretty funky orbit to cover the US, although I could be wrong, it's been a while.

As for the delay, this is somewhat to be expected. Most over the air systems use what is called Forward Error Correction (FEC) combined with Interleaving. The intent is that if there were no interleaving and a large burst of errors occured, the FEC could not correct the entire burst, and data would be uncorrectable. By adding interleaving data is spread out over time, sort of scrambled up. Thus if there is a large burst of errors only small bits of data for each time area get corrupted. Since these are actually small amounts of data after the receiver de-interleaves, the error correction can correct the data with no or minimal loss. The down side is that all of the data needs to be collected into a buffer before it can be deinterleaved adding to an initial delay either on acquisition or signal loss. This is also a design trade-off. The longer the time the data is interleaved, the more effective it is in minimizing errors, however it also adds to delay. It appears XM opted for a large delay to minimize errors. This seems reasonable since except for changing channels, the actual delay is rather transparent since it is one directional. Other systems, for example cellular phones, need to be very cognizant of the delay because it is a duplex (both directions) system and even a few hundred milliseconds of delay can be quite annoying as compared to the seconds of delay apparently on XM streams.

I couldn't find the info on XM's web site quickly for this post, but I seem to recall them bragging about their proprietary compression algorithm in the user agreement. This was probably done both for technical merits, as well as having a unique algorithm that can be protected with IP. This prevents anyone from legally building equipment to capture and decode the data streams. Note also in their user agreement that it states you can not record the content. While this doesn't have much impact on using XM in our TLs, it is yet another dig at hard won consumer recording rights just because the medium is digital instead of analog. The law says you can record broadcasts for personal use. I wonder how this would hold up in court? Having a proprietary codec certainly helps protect the content, at least while still in the digital domain.

As for the quality, I doubt it is "better than CD" since the original source for the most part was probably CD or worse. It doesn't get better than the source with compression, it only gets worse. I haven't had my TL long enough to really evaluate it. I've only had it a few days, and most of the time I've been in the car it has been with the family where I really couldn't crank up the tunes. From what I've heard so far it sounds better than most FM stations, but not as good as a CD, or even a high bit rate MP3 (>128 kbps). I really, really wish Acura would have included MP3 decoding. It's pretty sad when you can get a DVD player or portable CD player for less than $30 than will decode MP3 from a CD, but this very high end audio system will not. HUGE mistake Acura!

 

Hi, guys,

You can easily see how XM radio and Sirius radio work in this link.

XM Satellite Radio & Sirius Satellite Radio

XM's Rock & Roll almost stick by where they're (West coast and East coast). But Sirius' satellites are not.

 

edmiller9999,

Have you tried the ESL SS sound improvements I suggested in this "Improving your ELS Sound System" thread? I did some testing of the ELS SS with a Sound Pressure Level Meter, and posted the results.

It may help a lot, depending on what your complaints with the XM sound quality are. No guarantees, of course!

If you haven't tried it yet, give it a shot and let us know if you think it makes things better.

¿GotJazz?

 

I'm unhappy with XM sound quality as well. So much so that I would not be subscribing after the trial 90 days run out. It's not just that I expected better sound (although I did), it's that the quality and tone are tremendously inconsistent from channel to channel. That is some stations sound like there is too much base, some don't.

My radio is set for best quality of sound from CDs and I don't want to tinker with settings every time I switch to XM, and every time I switch from one XM station to the next. There is no such issue with FM stations.

 

I must be the only one to not care about the fidelity of the XM stations. Once I started listening to the comedy channels (150 and 151) I was hooked.

I was surpised that while going through the longest tunnel, in Minneapolis, I never lost the signal once.

 

Well, DUH! You like the talk stations so of course you wouldn't care much about the fidelity. XM signals are clear, without any interferences. But that's not enough for music.

 

There is a lot of technical talk about XM.. I have found:

1) Sound Quality

Different on different channels, but then again, recordings made differently especially at different eras.

XM says the sound quality is "Near CD" quality.. not better than CD....

Quoting algorhythms and whatnot is great... I find the sound quality better than FM by far on every musical channel.

2) Dropouts

I do not get ANY cut outs of XM ever... must have to do with where you live.. we have a lot of fall trees shedding as well(or we DID).

3) Programs

The variety is great... If you are paying 9.95 a month for ONLY "better than CD" sound quality, you probably shouldn't bother... but if you want all the choices XM offers, then you should for SURE.


In short, I could not IMAGINE not having XM in the car... you can only listen to your own CDs so many times until you are bored and want to hear something different. Sound quality... good.. bettetr than CD.. but what is ON the thing is what is most impressive!!

 

XM receivers have approximately 4 seconds of buffer, I was told. That is roughly what I experience. If I go under a freeway overpass during slow commute traffic for more than a few seconds, as happens to me a couple times every work day, I loose signal until I clear the overpass. Of course, I also loose XM signal in parking garages, tunnels, and other overhead obstructions. Several times I've lost the XM signal when a large truck or mountains are to the south of me. None the less the total percentage of loss signal has been much less than I expected so I don't find it very objectionable.

As far as XM audio quality, that is very subjective. Some people are very bothered by the distortion caused by digital compression and others aren't. If you are one of the lucky ones that aren't bothered by it just make sure you don't let someone like me show you what to listen for.