Bluetooth Transmitters and Latency

[Al Krow]

Bought myself a set of decent wireless headphones to complement my Smooth Hound wireless for when I'm required to "turn the bass down" at home by the rest of the family.

The first couple of bluetooth transmitters I've used have been poor in terms of latency (delay between playing a note and hearing it over the headphone) which makes trying to practice with them a non starter. No such latency issue with wired headphones so I can only put this down to needing to improve the transmitter.

The transmitter that arrived today was Trond's BT-Duo S which is supposed to have minimal audio latency, but it's still noticeable. At £25 I guess I shouldn't be expecting miracles.

Anyone recommend a decent bluetooth transmitter with minimal latency comparable to a wired headphone? Suggestions gratefully received!

Edited July 2, 2017 by Al Krow

[Cato]

I'm not sure it exists.

I looked into blue tooth wireless about a year ago,in all the systems I found reviwed, all of them had too much latency for live practice or performance.

[Al Krow]

[quote name='Cato' timestamp='1497902159' post='3321247']
I'm not sure it exists.

I looked into blue tooth wireless about a year ago,in all the systems I found reviwed, all of them had too much latency for live practice or performance.
[/quote]

Ok thanks very much for getting back to me even it is bad news! It will at least save me trawling through ever more expensive bluetooth transmitters...

My only ray of hope / challenge to us both is how do IEMs work, they obvviously manage to relay audio with negligible latency? Are they on a different protocol to bluetooth?

[obbm]

Anything digital will introduce delay. Analogue wireless is better. Copper to copper is best.

[BigRedX]

The latency of any Bluetooth headphones will always be too high as the protocol simply hasn't been designed for this kind of real-time, timing critical application.

[Al Krow]

Something not quite stacking up here though? The Smooth Hound wireless is digital with barely noticeable delay (nano seconds). The blue tooth transmitters I've tried so far have had latency 100s of times worse (1/4 of a second).

Just seen BRX's response. That makes sense. So how do IEM's work and is that what I need here?

Edited June 19, 2017 by Al Krow

[CameronJ]

BRX is right. Bluetooth literally isn't fit for this purpose as it was never designed for it. The quality of sound available through Bluetooth devices is actually quite decent but the latency is less than ideal (as you've noticed) range is fairly short and the strength of the connection can be compromised easily. As I understand it the Smooth Hound and similar digital systems run on technology akin to WiFi which allows for much better connection stability and transfer speed. Many wireless mics and IEMs work in the same way.

I have very little knowledge of analogue wireless systems, other than hearing comedic tales of bands picking up conversations from the local taxi office through their PA

[BigRedX]

[quote name='Al Krow' timestamp='1497908625' post='3321308']
Just seen BRX's response. That makes sense. So how do IEM's work and is that what I need here?
[/quote]

Id suggest that you start by having a read through the [url=http://basschat.co.uk/topic/205633-in-ear-monitors-help-needed/]IEM thread[/url]. AFAICS, the pro IME systems are still high quality analogue, although digital units with suitably low latency are starting to appear.

However if you do go for a digital system you still need to be aware of cumulative latency. While the latency of each of your individual devices in your signal chain may be low, once they are all combined, you could well be left with unsuitably high latency. The problem is that every digital device will add it's own latency converting the signal from analogue to digital and back again.

This wouldn't be a problem if the signal remained in the digital domain from your wireless transmitter on your bass to the receiver for your IEMs. But it doesn't.

[dave_bass5]

The two sets of Bose BT headphones i have will also work wired, and i made sure of this before buying them for exactly the above reason.

Forget BT if you need low latency.

[EBS_freak]

Here's some fun figures... for the average person, the maximum acceptable latency at your ear, is 10ms. That means that as soon as you exceed that, you'll notice a big disconnect between what you are playing and what you hear. The average latency for bluetooth is in the region of 30ms... so instantly, you will see that this is a non starter for IEM. Couple with the fact that the OP is using a Smooth Hound - which has terrible latency figures for a wireless system (8ms vs the typical figures of 3ms and below for it's competitors), the OP is on to a bit of a loser from the word go. In fact, having done some investigation into the OP's bluetooth device - the latency is 40ms.

So with a Smooth Hound and Bluetooth solution, you have approaching 50ms latency from those two devices alone... Are you going through a digital desk? Expect to add anything between 0.5ms and 3ms latency. What about digital fx pedals? again, 0.5-3ms per pedal... and in particularly processor heavy functions - such as pedals that transpose (excluding octaves), expect to at least double that.

So what BigRedX is saying is true - however, on higher end systems, there are some incredible advances where the audio does stay in the digital domain - there's dedicated Dante PCIe cards that allows for a round trip of digital comfortably under 1ms. Its far from cheap though. But once you are in this domain, you can run through specialist plugins with uber low latency (think figures around 2ms - many of which are run in parallel - so round trip within the digital domain is well under 4ms post all processing). Add the desk latency and you are still way, way under the 10ms target for IEM monitoring. So, for example, if you were using a pro digital desk (Digico, A&H iLive, Avid etc...), something like a Shure ULXD and say some Wave plugins, your could get your bass sounding whatever your wanted at under 5-6ms latency.

The ONLY acceptable digital IEM system is the newly introduced Lectrosonics Duet IEM - [url="http://www.lectrosonics.com/US/Wireless-IFB/category/218-iem-in-ear-monitor.html"]http://www.lectroson...ar-monitor.html[/url] - (latency figures are incredibly low for a digital wireless - 1.4ms for analogue sources, 1ms for digital (Dante)) expect to pay over 2k a channel... and in the UK, you will need a specific event or fixed site license as it is only available in frequency ranges that fall outside of the normal channel 38 and 70 license range. All other IEM solutions are analogue - like your standard FM radio. There are some IEMs that proclaim they are "digital" - in reality, that refers to the DSP that happens on the audio whilst it is in-between the radio transmission phase of the process - that radio transmission - yes, it's analogue, purely to keep the latency figures down.

With regard to digital over WiFi - the process is similar to analogue with the exception that instead of a compander (that squishes the signal into a payload that will fit in the available bandwidth) at the transmitter and a decompander at the receiver end (that tries to restore the signal to be comparable to the original signal pre-compander), it goes through two lots of digital/analogue conversion (with the resulting radio transmission transmission being digitally encoded). The advantage is that there is enough bandwidth to convert the analogue to digital and vice versa with no discernible loss of quality - however, you will introduce latency into the transmission as this conversion takes place. If you look at the specs of wifi compared to bluetooth, the available data transfer rate is 10 times that of bluetooth... hence you can soon understand why bluetooth has an impact on overall quality. Its worth noting that it's the quality of the compander that you pay for in analogue systems - some are great... some are terrible... and on bass, the first thing you'll notice on a cheaper system is the lack of low frequencies. On top end systems, you can actually cram a lot more channels of audio into the same radio spectrum... which means you can run channels of wireless systems in a smaller frequency range... and you can also encrypt... which means that people can't tune into the radio frequency and eavesdrop. Not so much of a problem for music... but it could be for conference rooms etc.

In short, BT is handy for phones and streaming audio - but it's a no go for real time performance. Go get a decent set of wired headphones!

Edited June 21, 2017 by EBS_freak

[Al Krow]

Hey EBS - meant to say sooner that is a VERY helpful explanation of latency. Thank you!

[bazzbass]

[quote name='EBS_freak' timestamp='1497990133' post='3321878']
Here's some fun figures... for the average person, the maximum acceptable latency at your ear, is 10ms. That means that as soon as you exceed that, you'll notice a big disconnect between what you are playing and what you hear.
[/quote]


I'd go a bit further and say that for a bass player or drummer, where precise timing is a priority, 5ms is as big a delay as you want.

yeah Bluetooth is ok for listening to recorded music but not for playing along to it. The cable isn't dead yet hehe