Understanding PESQ

Audio quality can degrade and be lost for all manner of reasons. A common scenario is when a call between two parties is routed through multiple network providers, each with its own set of transcoding and capacity management policies.

The quality of a business’s telephone service can have a major economic impact. Because conversations are hampered and key information must be repeated for accuracy, operational costs can rise as call durations increase. Customers may take their business elsewhere if they are dissatisfied, or new sales may not materialize due to poor audio quality. But how does a business find out if it has a problem with telephone audio quality?  


It’s time to put yourself in your customer’s shoes

 Only by dialing your numbers from the same country and using the same phone lines as your customers can you truly test the audio quality they are experiencing (and thus their perception of your brand when they call you).

This gives you the outside-in view of your customers’ experience while also alerting you to customer-impacting issues you might otherwise overlook.

Using over 70 in-country points of presence worldwide, Spearline’s testing solutions let you test your business-critical contact numbers. This internationally-recognized standard titled ‘PESQ’ is used for measuring audio quality that takes into account parameters like variable delays, noise on the line, and clipping of audio.  


And what does PESQ stand for? 

PESQ stands for Perceptual Evaluation of Speech Quality. Spearline uses this in its global in-country number testing. This objective and recognized industry-standard audio quality measure takes into consideration characteristics such as:

  1. – Audio sharpness
  2. – Call volume
  3. – Background noise
  4. – Variable latency or lag in audio
  5. – Clipping
  6. – Audio interference


The test compares an audio output (at the phone line’s ‘listener’ end) to the original voice file (played on the ‘talker’ side) to create a fully unbiased and objective indicator of the actual audio being heard. This is more accurate than other methods of audio quality measurement which often rely on audio quality predictions based on network performance. PESQ returns a score from -0.5 to 4.5, with higher scores indicating better quality.

With PESQ, audio quality on phone calls – mobile or fixed-line network; toll and toll-free services, VoIP or PSTN – can be assessed to an agreed international standard. There’s no ambiguity, so you know exactly how your phone services are performing.  


How to tell the difference between ‘good’ and ‘bad’ sound 

 PESQ score definitions are typically grouped into six bands.
The following audio samples for each band are real recordings of audio quality tests Spearline has run on customers’ international contact numbers:  


1.00 – 1.99 No meaning understood with any feasible effort

2.00 – 2.39 Considerable effort required

2.40 – 2.79 Moderate effort required

2.80 – 3.29 Attention necessary; a small amount of effort required

3.30 – 3.79 Attention necessary; no appreciable effort required

3.80 – 4.50 Complete relaxation possible; no effort required

From the examples given above, it’s easy to see how a customer could become irritated and drop a call if the audio quality is 1.11. A discussion between the two parties would be impossible. Conversations ranging from 2.00 – 2.79, would improve only slightly but would involve constant “could you repeat that?” or “sorry, I can’t hear you” which would further delay any problem getting resolved, frustrating the customer and possibly abandoning the call. It’s worth remembering, of course, that ‘good audio quality’ can vary from one country to the next. What one might expect in Germany would be unachievable in Brazil.

But if you’re proactively measuring the audio quality you’re achieving, and checking that against a country-by-country benchmark, you can make informed decisions about which telecoms providers you use, and how you route your calls. It’s not enough to just measure connectivity – a call doesn’t have to fail for the call to fail.  The call might connect, but the line has so much background noise that the customer hangs up. So, the call connection didn’t fail, but the call failed to generate the service or revenue you need it to.  


Alternative options

Similar to PESQ, POLQA (Perceptual Objective Listening Quality Analysis) provides a ‘full reference’ (FR) algorithm that compares the output of a test with an original reference signal to produce an objective measure of the difference between the two. Be sure to check out our blog, which gives an in-depth analysis of POLQA.  


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Find out more about Spearline

If you are new to Spearline and would like to find out more about how you can benefit from the platform, we would love to speak with you. Please send us a brief message, and we will be in contact with you shortly.

Spearline’s platform proactively tests inbound telecommunications services, as well as dial-out. Connectivity and audio quality are monitored on fixed-line, SIP, or mobile networks, globally. Spearline enables organizations to provide uninterrupted services to customers around the world. For further information, or if you have any further questions please get in touch with us.

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