It seems 'BlueTooth' LAGS! (for audio systems) - Page 1
Forum section: electronics / general

author: GlennSprigg
author_rank: Super Contributor
timestamp: December 31, 2019, 02:27:08 pm
content: I'm a 'muso' and have various instruments that I sometimes input to my Audio mixer/console,along with other people, for the likes of Guitars, Keyboards etc. I hunted everywhere for a'BlueTooth' transmitter to be received by a laptop, and a BlueTooth speaker system...That specific use does not seem to be on the market, and was finally explained to me 'why'!While you may for instance play music from your SmartPhone etc via BlueTooth, if that's allthat is playing then that's OK. However, if just ONE instrument like a guitar or keyboard isusing BlueTooth, and others are direct via cable, there is an inherent DELAY, making it allbut unplayable!! I guess it's all RF or nothing...

author: Nusa
author_rank: Super Contributor
timestamp: December 31, 2019, 03:08:48 pm
content: The guy using a 50-foot cable is going to have more delay than the guy using a 20-foot cable. Might not be enough for you to care about, but it's there. When you're wireless, it's just more fun, replacing length of wire with distance from the receiver (walking out into the crowd may be a really noticeable change). That's physics for you!And speakers are another example. Even if you have the signals to the speakers perfectly synced, you may need to adjust delays to account for the speed of sound from the individual speaker to the audience.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 31, 2019, 03:17:56 pm
content: Bluetooth has inherent (and non-fixed) latency, it's really not adapted to being used as real-time transmission of audio (note that when using those Bluetooth speakers, you don't care since the time reference doesn't matter in this case). The common wireless systems for musical instruments use much simpler protocols than Bluetooth.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 31, 2019, 03:52:17 pm
content: You have to use aptX in one of its low latency profiles for low latency.https://en.wikipedia.org/wiki/AptXOr use Wifi, which is very easy to get just a few ms of latency at enough bandwidth for uncompressed audio.

author: Cerebus
author_rank: Super Contributor
timestamp: December 31, 2019, 03:55:28 pm
content: Quote from: Nusa on December 31, 2019, 03:08:48 pmGiven that propagation of radio signals happens at the ubiquitous speed of light, it's not going to make a noticeable difference. Let's say you walk a mile into the crowd, that's 1760 yards = 1609m, which (taking the speed of light as 300 x 106ms-1) is going to add an additional delay of 5.36 us. Given that people don't tend to perceive audio delays below about 30 ms*, you're going to have to go another 5600 miles before you encounter a noticeable delay. A similar order of magnitude also applies to propagation of an audio signal by cable; even at a velocity factor of, say, 0.5 you still need 1000s of miles of extra cable length before a perceptible delay would accumulate.The noticeable delays in Bluetooth audio are all about the time taken in encoding, both at the audio (CODEC) level and at the radio (MAC packetisation etc.) level, not about the physics of propagation.*Most people won't notice the audio on a film or video being 1 or 2 frames out of sync and 30 ms is the accepted tolerance of this, that's where I'm taking my figure from. However, people are often better at vernier perception than absolute perception - we can detect a broken line (line the vernier on a scale) at a much smaller feature size than we can separate steps on a scale. Thus it's possible that we might perceive a difference in two audio events such as whether two drums are struck together orXmilliseconds apart at better than that 30 ms figure; I just don't have a figure for this but I'd guess that the minimum value would be at most 10 - 20 ms (For comparison a 1/64 note in 4/4 time at circa 150 bpm lasts 6 ms - that's about the fastest grace note that anybody can play).

author: Halcyon
author_rank: Unknown
timestamp: January 01, 2020, 12:08:08 am
content: I find the same delay in my car. If I'm playing video on my phone but streaming the audio via my car infotainment system, there is a good 2-3 second delay with the audio.During phone calls, the system seems to switch to a lower quality (but also much lower delay) codec.

author: Buriedcode
author_rank: Super Contributor
timestamp: January 01, 2020, 04:22:38 am
content: I'll second the Apt-x LL, they claim its 40ms, which is fine for lip-sync, but for instruments - when added to other delays in the chain, might go over the 60-80ms "noticable"mark (as in, you notice this, because you are producing the sound, you notice shorter delays than you can with eye-to-ear lip-sync). Bluetooth audio, in terms of quality has only really become quite good in the past 5 years, but it still isn't really meant for real-time, the bluetooth standard just has a lot to deal with to guarantee a certain latency.For wireless guitars I've used the nordic devices with limited success.

author: GlennSprigg
author_rank: Super Contributor
timestamp: January 01, 2020, 05:06:58 am
content: Thanks to youall. And toNiHaoMike. I hadn't thought about the encoding/decoding time.And your Wikipedia link toaptX. (Scroll down to the 'aptX Live' section).Side-Note:Regarding speed of electricity in cables... It puzzles me when people say that ittravels at the speed of light, but there is really no relationship! It's not propagating like light.You push electrons in one end, and the physical cascade pushes some out the other end!As for the electrons themselves, in a DC circuit with say 1 Amp flowing, the actual electronsare only moving about 1cm per Sec! (Or what ever).

author: DimitriP
author_rank: Super Contributor
timestamp: January 01, 2020, 05:28:17 am
content: QuoteLatency is a plague that hasn't been eradicated yet.It's not just bluetoth.Most USB "podcasting" microphones have an (analog) "monitor" port so you can actually hear yourself in real time.

author: BradC
author_rank: Super Contributor
timestamp: January 01, 2020, 08:04:46 am
content: Quote from: Nusa on December 31, 2019, 03:08:48 pmWhere that kills you is not the latency from the guitar to the speaker, but the latency from the speaker to your ear. When I play country pubs I like to go for a long walk to see what it sounds like from the paddock next door, but I'm always limited by the speed of sound as I gradually drift behind the further I get from the band. A wireless in-ear monitor would sort that, but I'm not that serious.

author: German_EE
author_rank: Super Contributor
timestamp: January 01, 2020, 09:48:41 am
content: The problem of audio latency occurs in many fields including RF communication. Radio amateurs sometimes use a Morse mode called QSK where the switch between transmit and receive is so quick you can hear the receiver between the transmitted dots. However, when constructing the transmit/receive circuit timing is everything and you need to take account of the 2 ms or so it takes for an audio signal to travel between the speaker and the operators ear.QSK using bluetooth would not work.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 01, 2020, 01:33:52 pm
content: I'm working on a two channel current sensor that sends the current waveforms to an inverter in real time. The end to end latency I'm targeting is a few hundred us at most. It's PLC rather than true wireless, but it shares a lot with wireless as far as tolerance to noise is concerned.