Understanding POLQA

Poor audio quality often means a customer can’t complete the objective of their call. It has a negative effect on average call duration, customer experience, and call abandonment rates for contact centers.

A majority of large corporations with call centers are aware of this, and they frequently pay their telecoms providers for the highest quality lines in order to supply their clients with the highest quality audio. 

However, carriers in digital networks can transcode audio quality from high-quality codecs like G711 to lower-quality codecs like G729 or GSM. This could be on a regular basis or only on occasion in order for the carrier to conserve bandwidth at those times of the day.

The contact center’s telecoms team has no insight into where transcoding is occurring, and even if they conclude it is, it may be impossible to locate and resolve with suppliers. So, what are the different ways of measuring audio quality in telecoms?

Do the POLQA

Similar to PESQ (Perceptual Evaluation of Speech Quality), 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.

The successor of PESQ – POLQA works in a similar way but can handle higher bandwidth audio signals including super-wideband (HD) and full-band voice signals, as well as the most recent voice coding and VoIP/VoLTE transmission technologies. Effects caused by new voice services like stretching and compression of speech signals in the time domain can all be easily handled by POLQA. The quality prediction for new and old codecs is improved and allows the direct comparison of AMR and EVRC. POLQA combines an excellent psychoacoustic and cognitive model with a new time alignment algorithm that perfectly handles varying delays.  

What does Spearline recommend?

The measures we recommend are as follows:


Final verdict (for now…)

We will never endorse MOS (Mean Opinion Score) as a reliable metric of audio quality because of its arbitrary, assumptive aspect, as well as its failure to take into account what’s going on outside of your internal network. MOS scales are defined in the ITU recommendations P.800, BS.1116, BS.1534, and others. A MOS scale simply defines a well-specified range of numbers that describe the quality as it is assessed by human subjects. A general misconception is, however, that these scales are something absolute and context-free. In reality, quite the opposite is the case. There is no such thing as an absolute MOS scale. MOS values are only valid within the context of the experiment that was conducted to generate them.

We use PESQ in the vast majority of our audio quality testing since the vast majority of voice calls are made over PSTN and telephone (which use narrowband codecs). We endorse it because it uses a real audio sample, allows for an end-to-end evaluation of the whole audio path (including audio sharpness, background noise, volume distortion, and clipping), and generates an objective metric from it. In most cases, as long as you’re not using wideband and HD voice, PESQ has no significant downside compared to POLQA.

POLQA is the easiest way to assess audio quality by using a wideband or HD voice. It tests a real audio sample, allows for end-to-end evaluation, and generates an analytical metric, similar to PESQ, but with the additional versatility of being able to be used with HD and wideband frequencies. It’s a measure we’re beginning to introduce as we find more of our customers using wideband and HD voice, but there’s no significant advantage to using it otherwise. If you’re using a standard narrowband voice, then PESQ is still your best option.  

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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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