Troubleshooting · Symptoms
Choppy Audio and Jitter: A Diagnosis Guide
Words arrive scrambled, syllables vanish, voices sound like they're underwater. Choppy audio is not 'the internet being slow' — it is packets arriving at irregular intervals (jitter) or not arriving at all (loss), and the receiver's jitter buffer running dry. The good news: jitter is measurable in any capture, and its cause is almost always a queue somewhere between the two talkers.
This guide shows you how to measure it, locate the congested point, and apply the fixes in the order that works — because 'buy more bandwidth' is the most expensive and least reliable item on the list.
The numbers that define 'choppy'
Voice is sent as a metronome: typically one packet every 20 ms. The receiver holds a small jitter buffer (30–60 ms is common) to smooth arrival variation. Quality collapses when:
| Metric | Good | Noticeable | Broken |
|---|---|---|---|
| Jitter (variation in arrival time) | < 10 ms | 10–30 ms | > 30 ms sustained |
| Packet loss (after concealment) | < 0.5% | 0.5–2% | > 2–3% |
| One-way latency | < 100 ms | 100–150 ms | > 150 ms (talk-over begins) |
Where jitter is born
Packets don't jitter in the middle of an empty network; they jitter in queues — the moment a link is full and a voice packet waits behind a bulk transfer. The usual crime scenes:
- Uplink saturation. Asymmetric connections (cable, DSL) have a small upload pipe; a cloud backup or photo sync fills it and voice queues behind it. The tell: calls degrade when someone uploads.
- Wi-Fi. Contended airtime, roaming between access points, and a phone at the edge of coverage. Desk phones on weak Wi-Fi are jitter machines.
- Bufferbloat. Oversized buffers in cheap routers/modems hold packets for hundreds of milliseconds under load — speed tests look fine while latency balloons.
- Missing or broken QoS. DSCP markings stripped at a boundary, or a QoS policy configured on a device the traffic doesn't cross.
- A genuinely congested WAN/ISP segment — real, but last on the list; prove it with captures at two points before accepting it.
Measure, locate, fix
- Measure first: in a capture of a bad call, open the RTP stream analysis — note jitter and loss figures. Also capture a good call for contrast (different time of day is typical).
- Correlate with activity: does choppiness track uploads, backups, or a specific hour? A pattern is a diagnosis half-made (see the peak-hours guide).
- Capture at two points (LAN side and WAN side of your router) during the same call window. Jitter present on the LAN side already → internal problem (Wi-Fi, local congestion). Clean on LAN, dirty on WAN → your router's queueing or the ISP path.
- Apply QoS properly: mark voice EF (DSCP 46) and signaling CS3, configure priority queuing for voice on the WAN edge, and confirm markings survive to the provider (see the QoS guide).
- Tame the elephants: schedule backups and syncs off-hours, or rate-limit bulk classes below voice in the same QoS policy.
- Get phones off marginal Wi-Fi: wire them, or fix coverage; no QoS policy repairs bad airtime.
- Verify with the same measurement: repeat the capture in the previously-bad window and confirm jitter back under ~10 ms.
Frequently asked questions
- Will doubling our internet speed fix choppy calls?
- Only if raw capacity is the binding constraint — which the two-point capture will show. On a saturated-but-fast link, more speed shrinks but does not remove the queueing problem; QoS plus sane scheduling fixes most offices at zero bandwidth cost.
- Why do calls sound fine in the morning and awful after lunch?
- Load. Something fills the uplink or the LAN in the afternoon (backups, syncs, a neighboring tenant, streaming). That time pattern is diagnostic gold — see the peak-hours guide for the full workflow.
- What jitter buffer setting should phones use?
- Adaptive buffers in the 30–60 ms range suit most networks. Bigger buffers mask jitter but add delay (talk-over); smaller buffers sound tight until the first spike. If you must raise the buffer to hide jitter, you have a network fault to fix, not a setting to celebrate.
Sources and further reading
Related guides
- Jitter, Latency, Packet Loss
- QoS and DSCP for VoIP
- Call Quality Collapses at Peak Hours
- Robotic or Metallic Voice