Introducing SigSound

The perception of voice quality in mobile networks is changing through apss such as WhatsApp and Zoom. SigSound is an accessory for SigMo devices to detect silent calls and one-way transmissions and a cost-effective path to test audio quality in 5G networks.


We completed an affordable and easy to deploy test system to help Communication Service Providers (CSPs) detect silent calls - SigSound. Inserting this unique dongle into our SigMo device and pairing it with another, allows test calls to be made on a continuous basis. Our system inserts tones which are detected at both ends.

CSPs can immediately identify call continuity problems. In that event, the SignalScore platform alerts the operations centre in real time of the failure and provides the call logs to diagnose and trace the fault. The system is remotely configurable to set test patterns. By siting test probes in various locations throughout a network, all the network functions can be exercised on a routine basis. Active SigMo devices will also conduct a range of other call tests such as call set up time, call set up failures and dropped calls.

SigMo and SigSound see the network as the customer does, truly mirroring the Quality of Experience while providing actionable data. SigSound sets the stage to look at signal degradation between expected and received and by extension provide an audio quality score.


The perception of voice quality in mobile networks is changing. Today, calls are increasingly made on WhatsApp, Zoom, Teams, Skype and other apps. Silent calls and one-way transmissions are annoying and frustrating non-alarming faults. It is a failure that upsets users and is one of the more difficult faults for engineers to diagnose and localise. We worked with a large MVNO that experienced the issue in significant numbers. Our month-long tests revealed that we quite often had to make three or four calls before we had two-way transmission. These faults were often happening across network interconnect points which further complicated the issue. The Service Providers first learned about the problems through calls to their call centre from fed up customers, which is the worst form of problem alarming. Through the deployment of SigSound devices we helped them track and address the problem.

Modern telecommunication networks of today have very sophisticated in-built service monitoring capabilities. These come as part and parcel of OEM nodes or function blocks and in the hardware servers and their operating systems. They are very good at telling the operator when a node has failed, or the throughput of traffic or signalling is not right. This capability from node vendors is often an ‘add-on’ in the pricing menus and does not come cheap. Often a vendor will include it as part of the overall pricing. Either way it becomes a capital expenditure so it gets wrapped up in project costs and that tends to suit the way must operators like to account for this.

At SignalScore, we focus in on the user experience. The right place to measure the service performance is at the device level, the contact point between the network and the customer. The benefits of this approach are monitoring trends in performance, benchmarking over time and against competitors, before-and-after checks when network upgrades are performed, testing new network features in the field where the customers are and looking for ‘non-alarmable’ events. In-built network features are useful to detect failures at the node level but not all service effecting faults raise alarms in the operations centres.


Testing audio quality starts by testing for a functioning channel. We consider POLQA a somewhat academic approach to voice testing. In contrast, SigSound provides a pragmatic and considerably more cost-effective alternative to provide a superior audio experience to customers. The devices are now available to Service Providers for trial and deployment.


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