Better sound through Bluetooth and Line-in than USB drive?

[Droid]

I'm curious if anyone else has seen this, and if I'm not imagining it, than why is this the case? Sound through Bluetooth or Line-in seems to sound "better" than when playing off a USB hard drive.

I'm not an audiophile, but the music seems richer through Bluetooth or the Line-in, as though it has more dynamic range.

This is exactly the opposite of what I'd expect, given that in the case of the USB drive, the audio remains as a digital signal until output. With the line-in, it's being converted to analog stereo by a phone. With Bluetooth, it's effectively being transcoded into an additional lossy compression format (i.e. re-encoding an MP3 a second time), adding a second layer of digital compression to it.

My only theories are (in order of likelihood):
1.) I'm insane.
2.) The DAC in the stock radio is crap. (Although I'd think it'd be used for Bluetooth as well, perhaps it's a different system).

This is on a 2011 with Nav.

 

[Rookie]

Lot of haunted trucks around here lately.

 

[SirCrush32]

I'm curious if anyone else has seen this, and if I'm not imagining it, than why is this the case? Sound through Bluetooth or Line-in seems to sound "better" than when playing off a USB hard drive.

I'm not an audiophile, but the music seems richer through Bluetooth or the Line-in, as though it has more dynamic range.

This is exactly the opposite of what I'd expect, given that in the case of the USB drive, the audio remains as a digital signal until output. With the line-in, it's being converted to analog stereo by a phone. With Bluetooth, it's effectively being transcoded into an additional lossy compression format (i.e. re-encoding an MP3 a second time), adding a second layer of digital compression to it.

My only theories are (in order of likelihood):
1.) I'm insane.
2.) The DAC in the stock radio is crap. (Although I'd think it'd be used for Bluetooth as well, perhaps it's a different system).

This is on a 2011 with Nav.

So your theory of being insane I can not answer.

But as far as a sound difference there is one.

Using an USB cable your sound is digital until it gets to the source and it becomes analog so that's why it may not sound as loud as when you use Bluetooth or aux cable. The proper term I believe when it converts from digital to analog is signal degradation.

Now when using an Aux cable its a direct audio connection with full bandwidth.

Bluetooth not too sure about but I know its digital and it sounds better than FM (which is mostly analog) and I believe I read somewhere it can block certain signals. Maybe someone with a bit more knowledge can chime in on the last one.

 

[AZEngineer]

It's digital over bluetooth and USB. I did some surfing and both should cover the full audio range of 20-20Khz. I also read alot of posts from folks claiming that the sound was lower volume with bluetooth and also lower quality.

I'm pretty picky and with my iPhone 5 bluetooth sounds just like USB.

Maybe your phone applies the equilizer settings to one and not other? try setting the EQ and audio settings flat and check?

 

[Droid]

So your theory of being insane I can not answer.

But as far as a sound difference there is one.

Using an USB cable your sound is digital until it gets to the source and it becomes analog so that's why it may not sound as loud as when you use Bluetooth or aux cable. The proper term I believe when it converts from digital to analog is signal degradation.

Now when using an Aux cable its a direct audio connection with full bandwidth.

Bluetooth not too sure about but I know its digital and it sounds better than FM (which is mostly analog) and I believe I read somewhere it can block certain signals. Maybe someone with a bit more knowledge can chime in on the last one.

Bluetooth might be sending the actual MP3 file, or it might re-encode into another digital lossy format first. The A2DP profile supports directly sending MP3 files if both devices support that format in their Bluetooth stacks. Both devices certainly support MP3 playback, but that doesn't mean the phone is able to transmit MP3s over Bluetooth, or that the truck is able to receive them. There is a standard media format called "SBC" that is mandated by all Bluetooth devices. SBC is another lossy compression like MP3, so it can degrade the music in transmission. I have no idea which implementation is more commonly used.

It's digital over bluetooth and USB. I did some surfing and both should cover the full audio range of 20-20Khz. I also read alot of posts from folks claiming that the sound was lower volume with bluetooth and also lower quality.

I'm pretty picky and with my iPhone 5 bluetooth sounds just like USB.

Maybe your phone applies the equilizer settings to one and not other? try setting the EQ and audio settings flat and check?

Good idea on the equalizer, but it looks like both the phone (Bluetooth) and tablet (line out) I tried had their EQs entirely disabled/flat.

My only theory on this is still that the digital-to-audio conversion path is somehow poorly implemented if the source is from the USB drive. Haven't tried a CD, still need to do that (still need to find one ).

Music from USB has always sounded somehow "wrong" in my truck (and also in brother's nearly identical Raptor), as though it's being run through a mild EQ...but badly.

 

[SirCrush32]

Bluetooth might be sending the actual MP3 file, or it might re-encode into another digital lossy format first. The A2DP profile supports directly sending MP3 files if both devices support that format in their Bluetooth stacks. Both devices certainly support MP3 playback, but that doesn't mean the phone is able to transmit MP3s over Bluetooth, or that the truck is able to receive them. There is a standard media format called "SBC" that is mandated by all Bluetooth devices. SBC is another lossy compression like MP3, so it can degrade the music in transmission. I have no idea which implementation is more commonly used.



Good idea on the equalizer, but it looks like both the phone (Bluetooth) and tablet (line out) I tried had their EQs entirely disabled/flat.

My only theory on this is still that the digital-to-audio conversion path is somehow poorly implemented if the source is from the USB drive. Haven't tried a CD, still need to do that (still need to find one ).

Music from USB has always sounded somehow "wrong" in my truck (and also in brother's nearly identical Raptor), as though it's being run through a mild EQ...but badly.

All vehicles that I have used my USB port has sounded not so good. Only time it sounded decent was when I plugged a usb stick in an aftermarket radio. So I've always used Bluetooth or Aux Cable.

I believe the degradation from going from digital to analog is the issue when it comes to using the usb cable. I wonder if its usb 2.0 or usb 1.0 port they're using.

 

[Droid]

All vehicles that I have used my USB port has sounded not so good. Only time it sounded decent was when I plugged a usb stick in an aftermarket radio. So I've always used Bluetooth or Aux Cable.

I believe the degradation from going from digital to analog is the issue when it comes to using the usb cable. I wonder if its usb 2.0 or usb 1.0 port they're using.

The USB cable will be a pure digital signal, it either gets there or it doesn't. In the case of anything other than an iPod/iPhone/iPad, they're using a USB subprotocol known as "USB mass storage", which is the same thing that is used when you plug that USB device into your computer. It's just reading the MP3 files directly from it.

It has to be happening after that point, like in the digital-analog converter.

 

[AZEngineer]

I am in the computer chip business and I've worked in the car and home audio space over the years. It's highly unlikely that at this price point the head unit uses anything but a single inexpensive D/A converter. It is almost certainly built into the chip that runs the head unit. That chip would also have the USB interface which is pure digital. The bluetooth is very much like a wireless USB. In fact most systems like this head unit implement bluetooth via a USB port on the board. So if anything bluetooth should sound worse not better.
1) Wireless can have data loss, interruptions in playback
2) Bluetooth is most certainly flowing into the chip via a USB port on the chip

IF bluetooth sounds worse it seems like it would have to be the phone.

I am pretty picky with audio, I designed, built, and sold home stereo speakers in the early 80s that sold for $2500 a pair to start and I sold pairs as for as much as $7000. My iPhone 5 bluetooth and USB sound the same to my ears. The iPhone 5 sounds much better than HD radio, and Sirius sounds like crap. YMMV

 

[Cruisin67]

My iPhone 5 bluetooth and USB sound the same to my ears. The iPhone 5 sounds much better than HD radio, and Sirius sounds like crap. YMMV

This is exactly what I have experienced as well. Particularly with the Sirius. It sounds like someone is firmly pressing a pillow over the speakers.

 

[Jgpenfield]

My understanding of digital and analog

All signals must be converted to an analog signal for your speaker to play them. The original digital signal can be compressed and of poor quality. The digital signal in an iPhone is compressed and will never be as good as a CD. If you have chosen a low bit rate to save space you might be listening to poor quality music from your iPhone because the original signal is compressed. But iPhones can store high quality digital files up to 256 MHz and sound very good.
However, this has to be converted to analog. iPhones use a cheap digital analog converter and this can ruin your tune quality. The line out uses this cheap DAC and so does the USB. The iPhone USB cable sends a poor quality analog signal to your receiver. Bluetooth sends a digital signal and this must be converted to an analog signal by the receiver. If your DAC in the receiver is worse than the iPhone DAC (unlikely) then you would have worse sound from the Bluetooth. Another problem is that the original signal can be degraded when sent via bluetooth.
iPhone 5 is more likely to send a direct digital signal via USB (it can send analog or digital) to the head unit than iPhone 4. But the head unit might not be able to receiver the digital signal if it is older and so it might instead be receiving a poor analog signal.
The answer to your question has many variables.
What you need to know are: what model iPhone. Does that model send a digital or analog signal via the USB to your particular head unit? If it sends a digital signal what bit rate is the signal stored at on your iPhone? Does your head unit have a good quality DAC? Is the bluetooth signal converted or compressed when it is sent from your model iPhone to your headunit?