Perceptual Evaluation of Speech Quality – a Standard
The perceptual evaluation of speech quality has become a telecommunications standard.
A standard is an agreed way of making a product, managing a process, delivering a service, or supplying materials.
Standards offer comfort. Standards give some predictability of outcomes; typically positive.
Standardizing is beneficial for many aspects of how we live, from standards for quality, performance, and safety, to standards for service delivery.
Subjectivity is a Matter of Opinion
Plato said, “Opinion is the medium between knowledge and ignorance”. However, our global telecommunications industry grew with opinions at the heart of quality management.
MOS, or Mean Opinion Score, is a methodology that historically originates from subjective measurements. With MOS, listeners would sit in a “quiet room” and score telephone call quality. The methodology used simple perception-based scoring for years and years.
It was dominant until the ITU (International Telecommunication Union) put some structure in place (in ITU-T P.800). The ITU specified that “the talker should sit in a quiet room with a volume between 30 and 120 dB and a reverberation time less than 500 ms (preferably in the range 200–300 ms). The room noise level must be below 30 dBA with no dominant peaks in the spectrum.”
This level of standardization at least ensured a consistent setting where the listeners would then put their opinions into play.
Adding Science to Telephone Call Quality
Spearline has paralleled the technology leap from hissing tapes and crackling vinyl in the music world to high definition digital audio. While we might return to the former now and again for the sake of nostalgia, the music industry focuses on providing ever-higher levels of fidelity.
Our telephone conversations have not evolved at the same rate, some might argue. This may be due to the telephone networks originating as government utilities under the PTT banner – Post, Telegraph, Telephone.
With privatization and deregulation, the private sector has invested more, and taken more risks in development. It may be due to the utility nature of a person-to-person phone call, but with the advent of multi-party conferencing and collaboration, audio quality has become much more critical.
Perceptual Evaluation of Speech Quality, PESQ, provides a more objective, scientific approach. Otherwise known as ITU-T P.862, PESQ arrived in 2001. It analyzes the speech signal and provides an end-to-end quality assessment for a network or characterizes individual network components.
With PESQ perceptual evaluation of speech quality, 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. You know exactly how your phone services are performing.
How Does This Science Help Businesses?
Businesses today are reaching out to wider markets. For many, the internet has become their shop-front. The phone is a major link to their customer. Consumers will use multiple modes of communicating such as email, web-chat, etc.
However, studies show that the phone call remains dominant. People welcome the opportunity to talk through their problems or have their questions answered prior to purchase.
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.