Now,we'll look at the metrics that were used to compile the rankings.
Initially, a call test audio file was sent. This was a 15-second test signal that included some interesting characteristics: male and female voices, with a low noise floor, correct speech audio levels (as opposed to artificially inflated volume or shouting); utterances of 1 to 3 seconds in duration (perfect for a "yes, I understand" utterance); intervals of silence (sounds about right), and consistent volume.
The Ranking Methodology included two key classifications. These were Most Reliable and Best Audio Quality.
Most Reliable used a complicated numerical computation to measure relative Service Availability, Average Number of Dial Attempts, and Dropped Call Performance Factors. Scoring method was calibrated to yield a maximum score of 100 points.
Best Audio Clarity assigned scores based on a mathematical formula involving a Mean Opinion Score (MOS) that measures the voice audio quality of a phone call on a scale of 1 to 5. This is dne by means of an algorithm called Perceptual Evaluation of Test Quality that contrasts a digital test audio file sent over a phone call with a reference copy of the same file. The goal is to see how much the audio degrades over the duration of the phone call.
The winners? Go to Part 3.