Jitter in plain terms
When packets travel across a network, each one takes a slightly different time. If they all take about the same time, the connection has low jitter. If some take 20 ms and the next ones 70 ms, it has high jitter. Formally, jitter is the variation in delay between packets, and the common way to measure it, used by the jitter test on this site and by most call software, is to take the difference in delay between each packet and the one before it, and average those differences.
Jitter matters because real-time apps need packets at a steady rhythm. A voice call plays a 20 ms slice of sound every 20 ms. If the next slice has not arrived when it is needed, the app has nothing to play. So call apps keep a jitter buffer: they hold incoming audio back for a short time so that late packets can catch up. The more jitter, the bigger the buffer has to be, and the bigger the buffer, the more delay you hear.
What jitter does to calls and games
- Voice calls: robotic or warbling audio as the app stretches and compresses sound to cover gaps; with very high jitter, dropped words.
- Video calls: stuttering video, audio drifting out of sync with the picture.
- Games: movement that looks smooth one moment and jerky the next; hit registration that feels inconsistent.
- Streaming and downloads: barely affected, because they buffer seconds of data ahead.
What is a good jitter?
| Jitter | Calls | Games |
|---|---|---|
| Under 5 ms | Excellent | Excellent |
| 5 to 15 ms | Excellent | Good |
| 15 to 30 ms | Good | Noticeable |
| 30 to 50 ms | Degraded | Poor |
| Over 50 ms | Poor | Bad |
Where jitter comes from
Wifi is the main source at home. Devices share a channel and take turns, and failed frames are retried, so each packet waits a different amount of time. The second source is queueing: when a line is busy, packets wait in the router's buffer, and the wait varies with how full the buffer is at that instant. The third is congestion on your provider's network, which varies through the day.
How to reduce jitter
- Use an Ethernet cable for the device that makes calls or plays games.
- Stop large uploads during calls; enable smart queue management (SQM) on the router if it has it.
- On wifi, use 5 GHz, move closer to the router, and turn off the adapter's power saving.
- Close other apps using the network on the same device.
- If jitter is only bad in the evening, it is provider congestion: report it with test results.
Very high jitter can look like packet loss to a call, because packets that arrive after the jitter buffer gives up on them are discarded. If you see both, fix the jitter first.