Bluetooth out-of-sync issue...

Thread Starter

Jim@HiTek

Joined Jul 30, 2017
50
Remodeling my RV's living room to incorporate "Theater seating" with a 47" TV as the center piece. As part of that I need to prevent cables from snaking across the floor to audio amplification equipment so I thought using this 3 in 1 USB Bluetooth Audio Transmitter/receiver would be the way to go. Since it's all modern and whatnot. Not to mention it's in a nice small package so it is non-intrusive.

And the devices work great to transmit the TV's audio to the receiver (another of the same unit only set to receive) plugged directly into the amp. The audio is crystal clear with wide dynamic range. But there is a problem...

The audio is out-of-sync. What I hear is delayed from when the speaker's lips on the TV move. Many times while watching shows this isn't an issue, but there are times when it's distracting, even disconcerting, when the lips stop moving and the audio doesn't.

The TV is a Vizio Smart TV and does have a 'Lip Sync' setting but when I use that, the sync gets worse. The settings are 0 to 5 and the closest sync is at 0, and gets worse if it set it higher. The amp does not have a lip sync adjustment.

Now you might all think that this is a lip sync issue between the video and audio between the transmitted RV TV, the HDMI from the satellite receiver and the TV's audio output...but nooooooo, it isn't that simple, because I also have a set of these Radio Shack Wireless 2.4 GHz devices and connected in the exact same way the Bluetooth devices are...from the TV's output to a transceiver's audio input than it's transmitted to the RS receiver, connected to the audio amp, and there is no audio delay. So the out-of-sync issue is in the Bluetooth devices only. Kind on interesting. Maybe it's built in? The ad copy for them, and the users guide that came with them, doesn't mention any purposeful delay.

So I'm just kind of looking for an answer to the question of why the Bluetooth hardware in the link above isn't in sync? Is this typical to all Bluetooth devices? I know, curiosity and the cat and all but, would still be interested in knowing why they do this.

Thanks for any input.
 

MrChips

Joined Oct 2, 2009
24,620
I am going to hazard a guess that the problem is inherent in all Bluetooth devices. The audio has to be collected, buffered, packetized and sent as a packet. At the receiver the reverse process takes place. All of this takes time.
 

Thread Starter

Jim@HiTek

Joined Jul 30, 2017
50
Inherent. Hmm. You'd think if it was, you'd see that mentioned in the ad copy for all those BT devices. Could be, not doubting you, just seems funny I haven't seen it mentioned. I don't recall any BT technology white papers mentioning that either, but of course I read those over a decade ago, maybe two.

That must mean these RS devices are analog. Likely, I suspect.

But it's remarkable how tiny these devices are to have built in audio delay considering the available audio re-sync'ing devices that have built in delay I've seen today are in 3"X 3" or 4"X 4" boxes suggesting lots of circuitry. And at over $100 too. Yikes.

Hey, just thought of something, maybe these BT devices could be used to make an audio echo device somehow. For a band's echo pedals. Now if those internal chips have some kind of delay adjustment, that might work. Cool.
 
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nsaspook

Joined Aug 27, 2009
8,904
Any digital wireless audio system will have some delay as that's the nature of the beast. Old school audio cables work just great but still can't fix all lip-sync issues.

 

KeithWalker

Joined Jul 10, 2017
2,042
I tried using a Bluetooth transmitter and a receiver for a PWM radio control link. The bandwidth was high enough and it did work very reliably but the delay of almost a second was unacceptable for my application.
 

MrSalts

Joined Apr 2, 2020
723
You are using a $6 Bluetooth device with, probably, a very slow processor. My kids each have Bluetooth surround systems in their living rooms and their is no lag in either setup. Get a better quality Bluetooth system.
 

Thread Starter

Jim@HiTek

Joined Jul 30, 2017
50
Interesting, MrSalts. As though this $6 device uses an RC oscillator instead of xtal? That could be, I suppose.

Seems a bit weird that something as annoying as poor lip sync wouldn't be mentioned by several competitors of the poor quality devices in their own ads for higher priced BT audio devices. How would one know where the price break is between the 'lots of lip sync offset' and 'little to no lip sync offset' if it's not mentioned?

Do you know what brand of BT systems your kids bought, MrSalts?
I have found some that advertise 'low-latency' and 'perfectly synced' at only $24 and up...but so far all I find the packaging is ugly or unsuitable. So, yeah, they are out there and I need to do a more thorough search.

Thanks!
 
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MrSalts

Joined Apr 2, 2020
723
Do you know what brand of BT systems your kids bought, MrSalts?
One has a several-hundred dollar Sonos system and one has something based on parts he cobbled together but likely cost him several hundred as well with Bluetooth enabled amp/receiver/multimedia hub, Bluetooth satellite speakers. I believe his system has some sort of microphone system the multimedia hub that controls the sync to the satellite speakers by delaying the video signal or the audio Bluetooth signal to sync everything. Good technology isn't cheap.
 

Thread Starter

Jim@HiTek

Joined Jul 30, 2017
50
Aww, I see. The licensing for the codex AptX is the difference. It's probably way overpriced so many manufacturers just wouldn't bother to use it.

That 40mS latency would likely be trivial to the average listener. No way I could detect it while watching lips move, IMO.

So that answers all my questions, I'll know what to search for the next time I want to buy a BT audio transceiver.

Thanks all.
 
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