XM Radio Distortion
12-02-2006, 12:47 AM
#1
Cruisin'
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XM Radio Distortion
Hey,
I just want to say first off, I've really learned a lot from this forum. I want to thank everyone who has put some much time and effort into creating such great DIY and fixes.
I am having a problem with my xm radio. There is some distortion from the radio. I know its not my speakers because the sound is amazing with DVD-A. I also fooled with the equalizer, and those settings didnt change the distortion. It sounds almost like a cheap electronic synthesizer. It also does it on all the channels. Really strange. I havent seen any posts on this subject so I was wondering if anyone knew anything about this?
Thank you,
NH
I just want to say first off, I've really learned a lot from this forum. I want to thank everyone who has put some much time and effort into creating such great DIY and fixes.
I am having a problem with my xm radio. There is some distortion from the radio. I know its not my speakers because the sound is amazing with DVD-A. I also fooled with the equalizer, and those settings didnt change the distortion. It sounds almost like a cheap electronic synthesizer. It also does it on all the channels. Really strange. I havent seen any posts on this subject so I was wondering if anyone knew anything about this?
Thank you,
NH
12-05-2006, 03:46 PM
#3
10th Gear
Join Date: Sep 2006
Location: Central Virginia
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The XM streams on some of the "lower" channels seem to be about 64kb which is very easy to notice poor quality. It is especially noticable when there is a special event happening on a "higher" channel (Sports).
12-05-2006, 11:04 PM
#5
Safety Car
hatchnu, as others have stated, the quality of XM radio isn't that great. Sometimes you will find that FM actually sounds better than some XM stations.
There should be a variation between the quality as you surf through the channels though. Some should sound ok, some good, and some just lousy. They should not all sound distorted.
When did your problem start? Recently or has it always been that way?
The XM antenna is located at the top of your hood. The receiver is located in the trunk behind the lining on the right side (near the navi DVD drive if you have it). XM is connected to the back of your head unit.
My XM subscription expired and since I don't use XM, I didn't renew. I only get about two or three stations and they all sound horrible. Is your subscription still valid?
If you believe that something might be wrong with your XM radio, then your best solution is to take it to a dealer for an inspection. It should be covered under warranty.
Good luck and please keep us updated!
There should be a variation between the quality as you surf through the channels though. Some should sound ok, some good, and some just lousy. They should not all sound distorted.
When did your problem start? Recently or has it always been that way?
The XM antenna is located at the top of your hood. The receiver is located in the trunk behind the lining on the right side (near the navi DVD drive if you have it). XM is connected to the back of your head unit.
My XM subscription expired and since I don't use XM, I didn't renew. I only get about two or three stations and they all sound horrible. Is your subscription still valid?
If you believe that something might be wrong with your XM radio, then your best solution is to take it to a dealer for an inspection. It should be covered under warranty.
Good luck and please keep us updated!
12-06-2006, 03:31 PM
#6
I addressed sound quality of various sources in another thread, and I think it provides a pretty summary of sound quality for various audio sources.
CD: If you want to think of a CD in terms of bitrate, a regular CD holds 700MB or 80 minutes of music. A quick series of calculations results in a bitrate of 1.167 megabits/sec. CDs are typically sampled at 44.1khz. Any additional sampling (such as DVD-A's 96khz) will not result in any additional human-perceivable audio quality. The highest frequency humans can hear is about 20khz, and according to nyquist sampling theory, 40khz sampling will result in reproduction of the entire human hearing range. Any additional sampling is unnecessary. (Insert discussion of discrete Fourier transforms here. Unless you have a degree in math, physics, or electrical engineering, then a discussion of DFTs would be beyond your comprehension, but go ahead and look it up in Wikipedia if you feel so inclined.)
iPod: I assume you have loaded your iPod with MP3s you downloaded from the internet. MP3s can have a WIDE range of bitrates. The bitrate of the MP3 is the number one indicator of its quality, but not that only one. Some MP3 encoders really suck and will produce crap even if the bitrate is high. The "typical" bitrate when MP3s were first produced is 128kbit. This is the minimum required for even remotely nice sounding audio. I have seen 96kbit all over the internet. 192kbit is maybe 1/3 or 1/2 CD quality. If you listen to a 128kbit MP3 (the most common bitrate) and then listen to a CD recording of the same song, you will be SHOCKED at how much better the CD sounds. You get used to listening to MP3 and you think that's what the song should sound like, but you would be mistaken. Even 192kbit, the highest common bitrate found online, pales in comparison to CD. The inconsistencies you are noticing from your iPod are that some songs you downloaded from the internet were 192 or maybe even higher, while others are 128 or maybe even lower.
XM - XM, believe it or not, uses a maximum bitrate of 56kbit for the popular stations and even lower for talk/sports/etc. Note that this 56kbit is NOT MP3. Here we should have a little discussion about "codecs". MP3 is one type of "codec". Others include windows media (WMA), AAC (itunes music store), and TwinVQ (Transform-domain Weighted Interleaved Vector Quantization). XM uses a highly efficient codec called "aacPlus". Different codecs have different efficiencies. 128kbit aacPlus music will sound a LOT better than 128kbit MP3 Music. Since XM uses a 56kbit aacPlus stream, I'd estimate its performance would be comaprable to somewhere between a 96kbit MP3 and a 128kbit MP3 - which, overall, is pretty poor. That's why if you take an XM tuner and listen to XM with very high quality headphones, or on a high-fidelity home stereo, it sounds like pure crap. Sirius suffers from the same low sound quality. The reason is because of the bandwidth for XM and Sirius is limited. XM is allowed a 12.5MHz chunck of the 2.3-2.4GHz range.
iPod: I assume you have loaded your iPod with MP3s you downloaded from the internet. MP3s can have a WIDE range of bitrates. The bitrate of the MP3 is the number one indicator of its quality, but not that only one. Some MP3 encoders really suck and will produce crap even if the bitrate is high. The "typical" bitrate when MP3s were first produced is 128kbit. This is the minimum required for even remotely nice sounding audio. I have seen 96kbit all over the internet. 192kbit is maybe 1/3 or 1/2 CD quality. If you listen to a 128kbit MP3 (the most common bitrate) and then listen to a CD recording of the same song, you will be SHOCKED at how much better the CD sounds. You get used to listening to MP3 and you think that's what the song should sound like, but you would be mistaken. Even 192kbit, the highest common bitrate found online, pales in comparison to CD. The inconsistencies you are noticing from your iPod are that some songs you downloaded from the internet were 192 or maybe even higher, while others are 128 or maybe even lower.
XM - XM, believe it or not, uses a maximum bitrate of 56kbit for the popular stations and even lower for talk/sports/etc. Note that this 56kbit is NOT MP3. Here we should have a little discussion about "codecs". MP3 is one type of "codec". Others include windows media (WMA), AAC (itunes music store), and TwinVQ (Transform-domain Weighted Interleaved Vector Quantization). XM uses a highly efficient codec called "aacPlus". Different codecs have different efficiencies. 128kbit aacPlus music will sound a LOT better than 128kbit MP3 Music. Since XM uses a 56kbit aacPlus stream, I'd estimate its performance would be comaprable to somewhere between a 96kbit MP3 and a 128kbit MP3 - which, overall, is pretty poor. That's why if you take an XM tuner and listen to XM with very high quality headphones, or on a high-fidelity home stereo, it sounds like pure crap. Sirius suffers from the same low sound quality. The reason is because of the bandwidth for XM and Sirius is limited. XM is allowed a 12.5MHz chunck of the 2.3-2.4GHz range.
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