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TV bluetooth sound delay

Discussion in 'Audio Visual' started by Donald_diy, 29 Nov 2020.

  1. Donald_diy

    Donald_diy

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    Hi all,have been considering a new bluetooth enabled Tv & external bluetooth speakers.

    After some google searching (google is not what it use to be!) it seems there could be a short but noticible time delay (lag) when viewing a person talking and voice. Out of sync.

    Tech is alaways changing. Anyone know of bluetooth equipment that does not delay or lag ?

    Bluetooth to speakers would make the installation so much easier but have also noticed 3.5mm headphone extension cables are available.
    Would a 5m headphone 3.5mm extension lead from tv to speakers have any detrimental effect on sound ?

    Sorry 2 questions,thanks in advance.
     
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  3. Wayners

    Wayners

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    5m lead will be no problem but Bluetooth lag can be. Sometimes there is a setting to fix the Bluetooth lag
     
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  4. Donald_diy

    Donald_diy

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    Thanks for the reply, going down the 3.5mm plug-plug cable extension now. Seems fool proof !
     
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  5. Lucid

    Lucid

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    Standard Bluetooth was never designed for audio, never mind audio that has to stay in sync with pictures, so trying to make it work for this is a bit of a fools errand.

    The original idea for BT was for transferring small data files wirelessly between two devices where there was no Wi-Fi connection. It didn't matter if it took a second or two to compress the data and unpack it at the receiver end.

    It then started to be used for low grade audio because it was convenient. For example, a BT link to a car stereo because the sound quality didn't matter in such a noisy environment. The compression process still took a long time relatively speaking, but again it didn't matter because when only listening.

    About a decade ago a chip manufacture called Qualcomm started to play around with the hardware and a new set of CODECs to improve BT audio quality. This was the original aptX format. Over time this expanded to include a broader range of CODECs, one of which addresses the time delay inherent in BT.

    A standard BT link has around 150 milliseconds of delay for the processing cycle. That's about an eighth of a second. Given that the average person can detect audio delays down to around 15 milliseconds (about a sixty-fifth if a second), and in the telecoms world people making a phone call would abandon it where the delay gets to 200ms, then you can see the gulf of work to do to make BT audio sync with a moving picture.

    One of the CODECs that Qualcomm developed is called aptX Low Latency. This reduces the processing delay down to around 40ms.

    TVs introduce some delay to the picture because of their image processing; 30 - 40ms isn't uncommon, and sometimes much longer. Console gamers know all about this because it affects game play when they press the button to duck and yet still get shot. The catch is that the TV also delays the audio to match. If the TV has a Lip Sync adjustment then it offers some way to adjust out part of the delay, but not all; and that's crucial.

    The bottom line here is that with BT there'll always be some perceptible difference in the sync between picture and sound.

    Where both the TV and the BT speaker have the aptX Low Latency CODECs then it's possible to reduce this to tolerable levels as long as you're not too fussy. Without it though I would say that it's quite hard to live with.



    The headphone audio cable won't have the same issue. Where you could end up with some problems is with noise if the cable isn't shielded well enough. There's also how the volume is controlled for the headphone out, and also the quality of the headphone amp inside the TV.
     
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  6. Donald_diy

    Donald_diy

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    Thanks for that info, blimey everyday is a school day.

    Hope its ok to ask another ask, Would this speaker set https://www.argos.co.uk/product/9163876 be ok with a new modern (budget) Tv sound connected via an extended headphone cable ?

    Many thanks again.
     
  7. Lucid

    Lucid

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    "Will they be okay?"..........That's really a How long is a piece of string sort of question :ROFLMAO:

    In very simple terms, yes, you'll get some sound from the powered speakers. As you probably realise though from the answer to the Bluetooth question, there's a bit more to it than that.


    "Am I going to blow anything up?" - Answer: Very unlikely

    "Will the speakers sound loud enough?" - Answer: Unknown, because it depends on...
    i) how much signal level the line input on the speakers needs (The speaker maker's web site doesn't list any info)
    ii) and the power output of the TV headphone circuit (Not generally a spec that the manual or brochure or website includes)
    iii) how lossy the headphone extension cable is

    "What will the sound quality be like?" - Answer: (Educated guess) Probably on par with a £50 sound bar

    The website for the manufacturer doesn't list much info, but I found a site with a mini review and it quoted a frequency response of 80Hz to 15kHz. What was missing is any figure for roll-off. This is normally given as -3dB or -6dB, but I have seen as much as -9dB. Where there's nothing quoted then it usually means that the figures are not that flattering.

    For sound, the dB figures tell me how quiet the bass and treble limits are compared to the average for the rest of the frequency range. A figure of -3dB at 80Hz tells me that the sound they measured at that point was at half the volume level compared to the average. -6dB is a quarter of the loudness. -9dB is an eighth of the loudness. Every -3dB step is a reduction by a half.

    Small speakers won't generally do good bass. That's just physics. What's slightly more concerning is the roll off at the top end. That's not untypical for small inexpensive active speakers, TBH, but it does mean that they lack a bit of top end sparkle. They'll be okay for dialogue but maybe not the first choice if music is important.
     
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