What jitter is, in one example
Imagine two connections that both average 40 ms of ping. On the first, every packet takes between 38 and 42 ms. On the second, packets take 15 ms, then 80 ms, then 25 ms, then 60 ms. Both have the same average, and they behave completely differently. The first is smooth. The second makes a voice call stutter and a game feel like the other players are teleporting. The difference between them is jitter.
This jitter test sends fifty UDP packets a second and records the delay of each. Jitter is the average change in delay between one packet and the next: if consecutive packets take 40 ms and then 50 ms, that step contributes 10 ms. It is the same measure voice and video software uses to size its buffers, and the same one most ping tools report.
How much jitter is too much
Voice apps cope with jitter by holding incoming audio in a jitter buffer for a moment before playing it, so that late packets still arrive in time. The buffer adds delay. With 30 ms of jitter the app has to wait long enough that conversations start to feel slightly out of step, and beyond that it starts throwing away packets that arrive too late, which sounds exactly like packet loss.
| Jitter | Gaming | Voice and video calls |
|---|---|---|
| Under 5 ms | Great | Great |
| 5 to 15 ms | Fine | Great |
| 15 to 30 ms | Poor for fast games | Fine |
| 30 to 50 ms | Bad | Poor: audio starts to break up |
| Over 50 ms | Bad | Bad |
What causes jitter
- Wifi. Wifi takes turns on a shared channel and retries frames that fail, so every packet waits a slightly different time. This is the most common source of jitter at home.
- Other traffic on your line. When your connection is busy, packets queue in the router. A queue that grows and shrinks produces jitter, and a very long one produces bufferbloat.
- Power-saving on the device. Laptops and phones put their wifi radio to sleep between packets, adding a few milliseconds at irregular moments.
- Provider congestion. Jitter that appears every evening and disappears overnight comes from your provider's network at peak times.
Fixes for each cause are in what is jitter and how to reduce it.
Reading the strip for jitter
On the packet strip, jitter shows as the ragged top edge. A low-jitter connection draws an almost flat row of short ticks. A high-jitter connection draws a jagged skyline. If the skyline is ragged all the way across, the cause is constant, and wifi is the usual suspect. If it is flat with a few tall towers, you have spikes rather than steady jitter; that pattern is covered in why ping spikes.