Circuit Merit
The Circuit Merit system is a measurement process designed to assess the voice-to-noise ratio in wired and wireless telephone circuits, especially the AMPS system, and although its reporting scale is sometimes used as input for calculating mean opinion score, the rating system is officially defined relative to given ranges of voice-to-noise ratios. Various technical sources state that experimental research varies in what ratio is required for good understanding, but is typically above 20 dB, and noticeably higher reports of voice quality can be achieved when the ratio is near 30 dB. There are 5 levels of quality, detailed as follows: Measurement of audio speech-to-noise ratios in a way which reflects interfering effects in a meaningful manner is difficult for the kinds of noise often encountered at mobile system receivers.