WiFi and Low-Latency Audio
The following is my "understanding," which probably means the following is thoroughly marinated in errors. (A lot of my "understanding" is a fragile house of cards based on reading and thinking abstractly about things I don't understand at a level that would survive questions in a PhD defense).
WiFi is not fundamentally (in the sense of a physics law) incompatible with low-latency communication. One can, in principle, use WiFi for low-latency audio, and there are principles for doing so that are somewhat methodical/systematic (it's not just "let's try it—oh wow, it happened to work, we're so lucky, I don't know why it worked").
However, if I were a music instructor helping a music student set up low-latency audio, I would possibly give them a shrink-wrap agreement similar to the following.
Sample agreement you can give your students
"By proceeding, I acknowledge that I have been warned that setting up audio technology can turn into a nightmare combination of reduced situational awareness, huge amounts of confirmation bias, and stress/freaking out. I have been warned that I should take every single opportunity to reduce avoidable cognitive load and potential need for troubleshooting. I have been warned that simple issues with simple fixes can balloon into 50-minute troubleshooting nightmares when people are stressed. I have been warned that straight-away choosing to use a hardwired Ethernet connection directly connecting my low-latency audio device to my router (an Ethernet switch (different from an Ethernet splitter) can be used, but I should refrain from having an intervening Google Home device, Time Machine, etc.) is one of the simple initial inconveniences I can take now to enormously reduce the potential for issues later on. I understand that no consulting fees are ever refunded for troubleshooting that results in a regretful 'I guess we should have used Ethernet to begin with, then we wouldn't have wasted 2 hours and damaged our emotional well-being.'"
What is WiFi?
WiFi™ is a collection of standards for using radio waves to transmit digital data between devices. A typical use of WiFi is to connect household devices (computers, smartphones/tablets, thermostats, etc.) to a router so that household devices can exchange data with the internet.
Why are so many implementations of WiFi bad for low-latency audio?
Multiple devices share a particular "portion" of radio spectrum by taking turns communicating with the router (rather than completely talking over each other simultaneously through the completely same portion of the radio spectrum).
"Taking turns" is not a WiFi-specific feature. Ethernet has this feature too. Two stations cannot transmit data at the same time on the same wire. Each station on an Ethernet wire is supposed to listen to the common electrical signal and wait for the absence of other traffic before beginning to transmit. There are procedures that stations follow when, on occasion, two stations begin transmitting so close to each other in time that their signals overlap (the electronic version of something vaguely like, "Oh, no, you go ahead"). In WiFi, collisions are actively avoided (cf. CSMA/CA).
For WiFi, however, the variability of the delay from "waiting to take turns" can be horrendous when the implemented way that radio spectrum is subdivided is not really up to the task of dealing with the number of devices that want to transmit/receive data in a given interval of time.
How can maximum latency of WiFi be improved?
The number of devices competing for a given portion of radio spectrum can be reduced in multiple ways:
- Turn off the WiFi antenna on each device in the household that is not essential for the low-latency session.
(Aside: To reduce interference on a channel in a high-density housing development, it would be also, in principle, beneficial to make neighbors shut off their WiFi networks, but such behavior is not prosocial).
- Dedicate a particular radio frequency band to the device used for low-latency audio and move all other devices that cannot help but continue to use WiFi to another band. For example, make the device used for low-latency audio connect to the router using 5 GHz WiFi (the corresponding SSID might even say something like 5G), and make all other devices that cannot help but still remain connected via WiFi connect to the router using 2.4 GHz WiFi.
- Make the low-latency device and the router communicate using radio signals that don't travel very far. Example: Use 5 GHz, or even 6 GHz, WiFi, instead of 2.4 GHz WiFi, between the low-latency device and router. 5 GHz and 6 GHz WiFi have shorter range. Using frequency bands with shorter range can reduce the number of other devices that are close enough to try to compete to communicate on the same band.
Even when the number of devices nearby trying to share radio spectrum cannot be reduced, it might be possible to improve the strategy used to subdivide and share a given portion of radio spectrum among those devices.
- WiFi is not "one thing." Standards have developed over time. WiFi 6 subdivides radio spectrum more finely (four times as many subcarriers per channel frequency) than WiFi 5. This is kind of like rearranging furniture in a restaurant that initially had a small number of large tables so as to have, after rearrangement, a large number of small tables. If local foot traffic consists of frequent arrivals of small groups of 1-2 people interested in dining quickly with little conversation, rather than sporadic arrivals of large families interested in extended stays, the restaurant subdivided into a large number of small-capacity tables can reduce the likelihood of potential customers needing to wait for seating. "Turn-taking" delay can be reduced by changing the WiFi standard used (upgrade from WiFi 5 to WiFi 6 or, even better, WiFi 6E).
- Ethernet Network Collisions | LiveAction https://www.liveaction.com/resources/blog/collisions/
- 10 Differences between Wifi 5 vs. Wifi 6 https://www.spiceworks.com/tech/networking/articles/wifi-five-vs-wifi-six/ Section 6