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 Post subject: USB vs Bluetooth audio
PostPosted: Tue Sep 06, 2011 10:37 am 
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Does anyone know if there is compression data loss (ie lower audio quality) over Bluetooth compared to USB (this is for an iPhone)? Or is it the same data by wire or wireless?

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PostPosted: Tue Sep 06, 2011 10:42 am 
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Definitely. The audio from my son's iPod Touch sounds like crap via bluetooth, but pretty good through the wired interface.

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PostPosted: Tue Sep 06, 2011 10:55 am 
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Perhaps I am not as discerning, but I thought Bluetooth audio sounded OK.
Maybe you should try it yourself.

Everything depends on the quality of the recording you are playing though.
(e.g., Don't expect 96kbps MP3s to sound great...)

Of all the audio sources, I think XM sounds the most over-compressed.


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PostPosted: Tue Sep 06, 2011 1:19 pm 
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I AM discerning, and I think BlueTooth (via my iPhone) sounds great; in fact, I have abandoned the wired connection (even though it has a nice interface) to take advantage of the seamless operation between phone and music. On the other hand, I don't think XM sounds that good, but if it was up to me I would remove that button! For iPods, it all depends on the quality of the source files.

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PostPosted: Tue Sep 06, 2011 1:45 pm 
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Stanton wrote:
I AM discerning, and I think BlueTooth (via my iPhone) sounds great; in fact, I have abandoned the wired connection (even though it has a nice interface) to take advantage of the seamless operation between phone and music.

There seems to be a difference in Bluetooth quality between my Android (Nexus S) and iOS (iPhone 4) devices. For whatever reason, Bluetooth seems to play at a lower quality off the Nexus than on the iPhone. On the iPhone, the quality between wired and Bluetooth is almost indistinguishable, but on the Nexus S there's a noticeable difference between Bluetooth and AUX.

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PostPosted: Tue Sep 06, 2011 2:10 pm 
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Packet: there definitely is a difference - for whatever reason, the bluetooth a2dp bitpool is hard-coded to a stupidly low value in most versions of android on the market (including the nexus). Why, I have no idea, but it causes a horrendous audible artifacting with some high frequencies (for example, moderate volume strings are suddenly accompanied by some crackling static-like noise). The only fix I've found for it is to use a mod (Cyanogenmod's latest version has the issue corrected, not sure about others).

If all else is correct, bluetooth audio has enough bandwidth that degradation, even at higher frequencies, should be below audible threshold for even discerning listeners, but there are all-too-often issues such as this one that get in the way, and are often completely unfixable by the consumer...

*edited to correct terminology, it's the bluetooth bitpool that is set low*


Last edited by defiancecp on Wed Sep 07, 2011 9:02 am, edited 1 time in total.

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PostPosted: Tue Sep 06, 2011 2:36 pm 
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Interesting! I couldn't tell any difference when playing the same high bit-rate content from the iPhone via bluetooth and wired USB but thought I'd ask... Funny back when satellite radio came out I used to think Sirius sounded better than XM (but both much worse than 160-192kbit mp3 or stuff from iTunes) but over the last few years heard some absolutely terrible compression on Sirius in my Prius. I haven't noticed any such artifacts (thus far) from XM in the Leaf. I know both Sirius and XM (now the same company) have the same bandwidth but not sure which is cramming more channels into it and I think they use different compression strategies. I don't know anything about Bluetooth audio but I assume the USB is sending the raw mp3 data over USB and the Leaf head unit is decompressing(??). I wasn't previously aware that Apple even had a method of pulling real time audio out of a iOS device over USB.

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PostPosted: Tue Sep 06, 2011 2:51 pm 
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OK - interesting about the Nexus vs iPhone.

I am using an iPhone 3, so it makes senses that the Bluetooth audio sounds OK to me compared to others with the Android phones who thought it wasn't as good.

When my XM trial runs out I don't plan to renew based primarily on sound quality, but also repetitive playlist.

Reasonably happy with the UI and sound quality when playing MP3s from memory sticks in the USB slot.
(I leave a flash drive in there all the time, and only fire up the iPhone wireless iTunes when someone else in the car wants to play DJ, for instance from the back seat.)


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PostPosted: Sun Oct 02, 2011 9:10 pm 
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Sound from USB connection off of iPhone 3GS sounds significantly better than BT..

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PostPosted: Sun Oct 02, 2011 9:53 pm 
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I think the audio through Bluetooth sounds fine.

The quality of XM radio varies wildly from really bad - talk radio - to just too many compression artifacts. There doesn't seem to be a way to find out what bit rate a XM channel is using but I would guess they are using 64 kbit for music and 8 k bit for talk.


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