Jitter test

Jitter is why a call breaks up on a connection whose speed test looks perfect.

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Jitter is the variation in latency between consecutive packets. If ten packets arrive 20 ms apart and the eleventh arrives 90 ms later, that gap is jitter — and it is the reason voices turn robotic, video freezes for a beat, and games rubber-band while every headline number on your speed test still looks healthy.

This test measures it the way real-time protocols do: the mean absolute difference between consecutive round trips, computed in arrival order. That ordering matters. Sorting the samples first and then measuring the spread produces a nice-looking number that describes nothing a call would ever experience.

Why jitter breaks calls and speed tests do not catch it

Voice and video are streams with a deadline. Each packet has a moment when it must be played, and one that arrives late is not late — it is lost, because the moment has passed. Applications hide this with a jitter buffer that holds audio for a few tens of milliseconds before playing it, but the buffer can only absorb variation it was sized for. Beyond that, you hear the gaps. A bulk download does not care about any of this, which is why throughput can look excellent on a connection nobody can hold a call on.

What causes it

WiFi contention is the most common source: every device sharing the band takes turns, and the wait for a turn is not constant. Overloaded router queues add more, especially while something else is uploading. Powerline adapters, interference from neighbouring networks, and aggressive power saving on laptops and phones all contribute. Wired connections to an uncongested router typically show jitter under 2 ms.

Reading the result

Below 5 ms is excellent and will never be audible. 5-20 ms is normal for WiFi and fine for most calls. Between 20 and 50 ms, longer calls start to develop dropouts. Above 50 ms, real-time use is genuinely degraded, and the fix is usually the wireless hop or the router queue rather than the internet connection itself.

Frequently asked questions

What is a good jitter value?

Under 5 ms is excellent, under 20 ms is fine for video calls, and above 50 ms will cause audible dropouts and stuttering video.

Why is my jitter high but my speed good?

They measure different things. Throughput is about volume over time; jitter is about the consistency of individual packet timing. WiFi contention and router queueing wreck the second while leaving the first untouched.

How do I fix high jitter?

Move to Ethernet or 5 GHz WiFi, get closer to the router, stop large background uploads during calls, and enable Smart Queue Management (fq_codel or CAKE) if your router supports it.