WiFi audio in live music
Audio WiFi in a music venue
The problem with using WiFi for point to point audio in a live venue
It may be possible that WiFi latency is a product of a system that is not set up for low latency. And that it may be possible to produce good quality audio with less than 6 ms of delay with a well designed system. A typical WiFi network with a small number of connected devices will have 50% of the packages will have a delay of less than 2.5 ms, 90% less than 12.0 ms and 1% more than 45 ms. Some packages could have a delay of over 500 milliseconds. A 5G network can achieve delays of only a few milliseconds.
Whilst it is possible to provide WiFi connectivity in “real-time with minimal delay”. The problem with this is that as the levels of interference increase, then the delay due to latency will increase. So, it may be possible to deliver this in a controlled environment. But if there are a lot of WiFi devices nearby, the time delay and audio quality will increase as the device has to work harder to correct for errors. It is possible that interference could occur from the large numbers of WiFi enabled devices in the audience. But for this to occur, there would need to be something in the venue for the phones to connect to. So this system should work well in venues that do not give the audience access to WiFi.
A possible solution for using audio over WiFi
Multiple channels and multiple antennas
MIMO, multiple-input and multiple-output. Long term, 802.11ac has the headroom to support up to eight antennas each running at over 400 Mbps each. A bandwidth of between 1 and 1.4 Mbps may be acceptable for audio use depending on the amount of compression due to FLAC, which leaves plenty of opportunity to use the extra available bandwidth to compensate for these problems. The same signal could be sent over more than one channel at the same time, so that if the data is delayed in one channel, it can still get through on another one. A minor issue is that greater numbers of antennas will increase the size and cost of the devices. Which makes it harder to produce a small XLR or Jack plug.
5G solves all of these issues. More about this in our post about 5G advantages for live music
More on WiFi use for audio
How can the quality of a WiFi network be improved for use with live audio?
It may be possible that WiFi latency is a product of a system that is not set up for low latency. And that it may be possible to produce good quality audio with less than 6 ms of delay.
On a normal home WiFi you should see no more than 2ms-3ms of latency. Again, this is really just processing time on your AP/Router. If it is heavily congested or you have a lot of collisions on your wireless, you can see it go as high as 4ms-6ms. Any higher latency indicates a poor connection or interference.
One way of reducing the latency would be to have one transmitter and one receiver for each audio path.
The root cause of jitter and latency on a WIFI network is a combination of the available bandwidth, number of people using the connection and interference – thus to improve latency you need to improve these aspects. Jitter is caused by variance in the amount of bandwidth being used.
The lower the speed of the connection the higher the latency. The more interference the lower the available bandwidth. The more people using the connection the greater the jitter. The more interference from other devices which are not always transmitting, the greater the jitter.
Newer hardware obeys newer standards, which make better use of the spectrum. Newer devices allow 40 megabit channels on the 2.4 GHz band and up to 160 megabit on the 5 GHz band. More bandwidth = lower latency.
Make sure the WIFI drivers are good – WIFI drivers can be a bit hit and miss – and they can very much affect latency and jitter.
You can implement QoS – by better scheduling packets you can reduce jitter and make better use of available frequency. You may also be able to reduce latency. This works better on the sender side than the receiver
Fragment packets (ie use a smaller MTU). This will reduce latency but also decrease speed. This is not easy to do and can break connectivity.
Firewalls filter all outgoing and incoming network traffic which takes up time. Disabling firewalls can help.
Routers sometimes need rebooting to solve latency issues.
As WiFi transmitters cannot detect collisions while sending data. So, WiFi relies on collision avoidance (CSMA/CA), where each sender attempts to avoid collisions by transmitting only when the channel is sensed to be idle, and then sends its full message frame in its entirety. Once the WiFi frame is sent, the sender waits for an explicit acknowledgment from the receiver before proceeding with the next transmission.