VoIP Call Quality: What Affects It and How to Fix Problems

Poor VoIP call quality costs you credibility with customers and patience with colleagues. The frustrating part is that most businesses assume it means they need faster broadband — but speed is almost never the issue. The real culprits are usually hiding in your router settings or your connection type, and they are straightforward to fix.

The short answer:

• VoIP call quality degrades when latency exceeds 150ms, jitter exceeds 30ms, or packet loss rises above 1%
• Each VoIP call only needs around 100Kbps — your connection speed is rarely the problem
• The most common cause is QoS not being configured on your router
• ADSL connections produce poor VoIP performance and are being switched off in January 2027 anyway
• Most issues can be resolved without upgrading your broadband

The three things that actually affect VoIP call quality

Voice over IP works by breaking your voice into small data packets, sending them across the internet, and reassembling them at the other end. When that process goes wrong in any of three ways, you hear it immediately.

Latency

Latency is the delay between speaking and being heard. It is measured in milliseconds (ms), and the acceptable threshold for a natural-sounding conversation is under 150ms. Above that, you get the awkward satellite-call effect where both parties keep talking over each other.

Latency over 300ms makes a call feel genuinely broken. Anything under 80ms and most people cannot perceive any delay at all.

Jitter

Jitter is inconsistency in packet arrival times. Even if your average latency is fine, packets that arrive in irregular bursts cause choppy audio, robotic voices, and clipped words. The acceptable threshold is under 30ms of jitter.

Jitter is almost always a network problem rather than a broadband speed problem. A router that is not prioritising voice traffic will let other data jump the queue, and voice packets arrive in uneven waves.

Packet loss

Packet loss happens when data packets do not arrive at all. VoIP can tolerate a tiny amount — under 1% — without audible effect. Above 1%, you start hearing gaps, crackles, and missed syllables. Above 5%, calls become unusable.

Packet loss is the most damaging of the three. Unlike a file download, VoIP cannot simply retry a lost packet. The gap in the audio is permanent.

The most common causes in UK business setups

Most VoIP quality problems trace back to one of five root causes.

QoS not configured. Quality of Service is a router setting that tells your network to prioritise voice traffic over everything else. Without it, a staff member downloading a large file or a Teams video call can starve your VoIP calls of the bandwidth they need. QoS is the single most impactful fix for most businesses, and it costs nothing.

ADSL connections. ADSL delivers broadband over copper phone lines, and it produces higher latency and far more jitter than fibre. It was never designed with real-time voice in mind. ADSL is also being switched off as part of the PSTN retirement in January 2027, so if you are still on it, a move to fibre is coming regardless.

Poor FTTC performance. Fibre to the Cabinet (FTTC) runs fibre to a green street cabinet, then copper to your premises. The copper segment introduces variability, especially on long line lengths. FTTP (Fibre to the Premises) runs fibre all the way in, eliminating that variability entirely.

Wi-Fi. Wi-Fi introduces jitter by design. Wireless networks share spectrum with neighbouring networks and household devices, and they retransmit packets constantly. A wired Ethernet connection from your phone or computer to the router eliminates a significant source of jitter in one step.

An overloaded or ageing router. Budget routers struggle to manage QoS effectively, especially under load. If your router is more than five years old or was supplied free by a consumer broadband provider, it may not support the QoS configuration that VoIP requires.

How to diagnose a VoIP call quality problem

Do not start by guessing. Run a structured test and you will usually identify the problem in under ten minutes.

Step 1: Run a VoIP-specific quality test. A standard broadband speed test measures download and upload speed — it tells you almost nothing about VoIP suitability. Use a VoIP-specific test that measures latency, jitter, and packet loss. You are looking for: latency under 150ms, jitter under 30ms, packet loss under 1%.

Step 2: Run the test under load. Run the test once with nothing else happening on the network, then again while someone streams video or downloads a large file. If your results degrade significantly under load, QoS configuration is your problem.

Step 3: Test wired versus Wi-Fi. Plug directly into your router with an Ethernet cable and run the test again. If your numbers improve, Wi-Fi is contributing to the problem.

Step 4: Check your connection type. Log into your router or ask your ISP whether you are on ADSL, FTTC, or FTTP. If you are on ADSL, that is likely the primary cause of your quality issues, and an upgrade is overdue.

Step 5: Check for bandwidth hogs. Look at what else is running on your network. Cloud backups, software updates, video conferencing, and large file syncs all compete for bandwidth. Even with QoS configured, understanding your network load helps you manage it properly.

How to fix VoIP call quality issues

Work through these fixes in order. Most businesses resolve their issues at step one or two.

Enable QoS on your router. Log into your router's admin panel (usually 192.168.1.1 or 192.168.0.1) and look for QoS or traffic prioritisation settings. Set voice traffic — typically identified by SIP or RTP protocol, or by the IP address of your VoIP device — to highest priority. If you cannot find QoS settings, your router may not support it and should be replaced.

Switch to a wired connection. Move your desk phones or the computer running your softphone onto Ethernet rather than Wi-Fi. This is the fastest, cheapest improvement available and has an immediate effect on jitter.

Upgrade from ADSL to FTTP. Full fibre is now available to the majority of UK business premises and is often cheaper than you expect. FTTP delivers dramatically lower and more consistent latency than ADSL or even FTTC. Given the January 2027 PSTN switch-off, moving to FTTP now avoids a forced migration under pressure later.

Replace an ageing router. A business-grade router with proper QoS support makes a significant difference. You do not need to spend a lot — a mid-range business router from a reputable manufacturer will handle VoIP traffic far more reliably than a free consumer router.

Identify and schedule bandwidth-intensive tasks. Configure cloud backups and large software updates to run outside business hours. This is a free fix that reduces network contention during the working day.

How VoIPninjas approaches call quality

VoIPninjas is a direct UK VoIP provider based in Christchurch, Dorset — not a reseller adding a margin on top of someone else's service. That distinction matters when something goes wrong.

When you call a reseller with a quality problem, they tell you to contact your ISP. When you call VoIPninjas, our team can look at your connection at the network level, identify whether the issue is on your side or ours, and give you specific guidance rather than a scripted response.

We offer a free 14-day trial on all plans so you can test call quality on your own connection, with your own devices, before you commit to anything. Our plans run on 28-day rolling agreements — Ronin at £5.99, Samurai at £14.99, and Shogun at £24.99 per user per month — so there is no contract pressure if your setup needs more work.

The trial is the right place to start. You will know within the first few calls whether quality meets your standard.

Try VoIPninjas free for 14 days. Test call quality on your own connection with no contract and no commitment. If it does not perform, you owe us nothing. Start your free trial → — or call us: 0330 043 2388 No tie-in, no setup fees. Most businesses are fully live within 10 working days.

Frequently asked questions

How much bandwidth does a VoIP call use?

Each active VoIP call uses approximately 100Kbps in each direction. A business with ten simultaneous calls needs around 1Mbps of dedicated bandwidth for voice — well within what any modern broadband connection can deliver. Bandwidth is rarely the problem. Consistency, jitter, and QoS configuration are what matter.

Will upgrading my broadband speed fix VoIP call quality?

Not usually. Moving from 40Mbps to 80Mbps FTTC will not improve your VoIP quality if QoS is not configured or if the copper line to your premises introduces jitter. Upgrading from FTTC or ADSL to FTTP will help, because full fibre delivers more consistent performance — but the improvement comes from lower jitter and latency, not raw speed.

Is VoIP call quality worse on Wi-Fi?

Yes, reliably so. Wi-Fi introduces jitter because wireless networks share spectrum, experience interference, and retransmit packets. A wired Ethernet connection between your device and router eliminates this variable entirely. If you use VoIP on a laptop, a USB-to-Ethernet adapter and a short patch cable will make a noticeable difference.

What is the PSTN switch-off and how does it affect VoIP?

BT's PSTN (Public Switched Telephone Network) and ISDN services are being retired in January 2027. After that date, all voice calls in the UK will travel over IP networks. Businesses still on ADSL or traditional phone lines will need to migrate regardless. Moving to VoIP now — on a decent broadband connection with QoS configured — means you make the transition on your own terms rather than under a deadline.