B2 left and right channels reversed via bluetooth

[Dougwzz99]

So I've recently acquired a B2. As part of the setup I've transferred a test signal MP3 file to check left - center - right channels. I've found that while left and right channels are just fine via the line out connection, via the bluetooth dongle they are reversed! 

I've double checked this by playing the exact same file via NAS on my PC using Windows Media Player (using both hard wired and bluetooth speakers). Left and right exactly as they should be. B2 line out left and right are correct. But via the B2 bluetooth dongle (I've tried soundbar and headphones) left and right are reversed from what they should be. 

I've also tried ripping a couple of CD's where I know certain instruments are on the left or right. Exactly the same - playback fine via line out, channels reversed via bluetooth dongle playback.

I don't understand why this is happening? Is there a fault with my B2?

Doug. 

[Mark Fishman]

The way I read your diagnostic tests, you tried using the B2's Bluetooth dongle on your PC, and bluetooth channels reversed there, also. If that's true, it's the dongle, not the B2, that's reversing the channels.

Have I misunderstood?

[Dougwzz99]

The left and right channels are fine using the PC's built-in bluetooth. I am using the bluetooth dongle on the B2 as supplied with the B2. I have not removed the dongle from the B2 at all. The channels are only reversed on the B2 using the dongle as supplied with the B2.

[Daniel Taylor]

I just tried playing a song with distinctly different instruments playing in the left and right channels.  Playing through HDMI to my A/V receiver put the instruments in the same channels as playing through my stereo Bluetooth speakers.  So that seem to indicate that it's not a design flaw - unless HDMI and Bluetooth both are reversed.

I tend to think that the Bluetooth dongle would simply broadcast whatever was given to it to send.  I could be wrong about that.  Are you using the Brennan Bluetooth dongle that was provided with the B2?

If you're using the directly wired speaker connections to the B2, it might be worth double checking which speakers go to which connectors.

[PMB]

Hi Doug,

There is a L-R swap option in the Maintenance menu but I think it will swap the Line Out also - give it a try.

Paul

Brennan Support.

[Mark Fishman]

>> "There is a L-R swap option in the Maintenance menu but I think it will swap the Line Out also"

"Also"? or "only"? The description of this menu entry says nothing about Bluetooth. Perhaps it's already set, and the problem is that the B2's Bluetooth is right but the system's been laid out for the swapped analog signal?

[Dougwzz99]

I am using the dongle as supplied by Brennan with the B2.

I've tried the L-R swap option in the Maintenance menu, it does correct the issue for Bluetooth. However as you said it also performs the swap on the Line Out so that is now reversed! 

This is probably good enough for me, as I intend to primarily use Bluetooth Out for my audio connection. It does suggest however that there is a (software?) issue with the Bluetooth setup on the B2 that really should be fixed?

Thanks

Doug. 

[Mark Fishman]

I see many reports of Bluetooth connections from phones -- iPhones, onePlus phones, and others -- having reversed audio channels relative to their direct (wired) connections, to all sorts of receiving devices: headphones, cars, pairs of free-standing speakers. So whatever is going on it is probably not limited to the B2.

In the case of the B2, though, all of the Bluetooth electronics os in the dongle. Without it the B2 has no Bluetooth capability at all. It is entirely possble that the problem is also in the dongle, not in the B2. That is whay I asked if you had tried using the dongle itself on your PC, to see if the problem travels with the dongle. Also, the Bluetooth dongle used by the B2 is BT4; if you're using BT5-compatible output devices, there could be unspecified behaviors.

I worked for 30 years on communication systems. Apparently it's quite easy to write a spec that neglects to nail down basic things like channel orientation, and different manufacturers can easily interpret the spec differently, so that some pairs of equipment work together, and others will exhibit "anomalies": but all the individual pieces are complying with the spec. While I haven't ound a VBluetooth spec that I can make sense of, one thing I found out is that the audio-over-Bluetooth function actually uses the *video* portion of the spec if you're sending more than one channel of audio, and that having a reverse channel (e.g., for a microphone) isn't actually in the spec, but has been finessed after the fact.

So it's messy. You can't say for certain that one particular device is the problem until you've changed out the other bits to see if the problem remains.

[Daniel Taylor]

Mark,

When you have a USB Bluetooth dongle, does the computer see it as just another USB audio device, with no Bluetooth awareness needed?

[Mark Fishman]

I'll have to give that a test -- my desktop computer has no in-built Bluetooth, but the OS (Windows 10) should know what to do with it. It's the same OS on my laptop, and *that* has Bluetooth...

On the B2, while there's no BT hardware without the dongle, the software support comes from the Linux OS running on the RPi. You'll recall that's why the B2B software version was introduced, to get the newer (and presumably better) Bluetooth support in the newer Linux kernel.

[Daniel Taylor]

Ah yes, now that you remind me I do remember the reason for the B2B release.  Ha.

So I guess the dongle does requires a software driver.  And I suppose that software could get the channels reverse.  But on my B2 with B2B software and a Brennan dongle, the channels are not reversed.  I don't see how a dongle could go bad in that particular way, but it'd be worth trying it with a device other than the B2, like you said, to see if the problem travels with it.

[Dougwzz99]

After some degree of fiddling around with various drivers (the built in Windows 10 drivers did not work, needed specific CSR drivers) I have successfully moved the B2 (CSR) dongle to my Windows laptop. The audio there works fine, left and right channels correctly where they should be. I suppose an interesting test would be to try a different dongle on the B2, however I have a feeling I'd run into similar driver issues if i tried that and my Linux knowledge is not up to dealing with those sort of issues. 

As I mentioned earlier the L-R swap in the B2 Maintenance menu resolves this for me, so I'm not going to risk what I have by trying to activate a different dongle on the B2. 

Thanks all for the assistance.

Doug.