Receiver Loudness Rating

Description

The Receiver Loudness Rating (RLR) is a fundamental acoustic parameter defined in the 3GPP and ITU-T specifications (e.g., ITU-T P.79) for terminal equipment. It is part of a family of 'Loudness Ratings' that model the end-to-end transmission loss in a telephone connection. Specifically, RLR characterizes the sensitivity of the terminal's receiving path—from the electrical input at the receiver (the earpiece or loudspeaker) to the acoustic output at the user's ear. It is expressed in decibels (dB) and represents the loss (or gain) in loudness; a lower RLR value indicates a louder receiving sound. The measurement is performed under standardized conditions using an artificial ear (IEC 60318-4) and specific test signals (e.g., pink noise or speech-shaped noise) to ensure reproducibility. RLR is calculated by comparing the measured sound pressure level at the artificial ear to a reference level. It is a critical component in the overall loudness calculus, which includes the Send Loudness Rating (SLR) for the microphone path and the Overall Loudness Rating (OLR) for the complete connection. Network planners and terminal manufacturers use RLR values, along with assumed sidetone and network losses, to design systems that meet target loudness objectives, ensuring users experience comfortable and intelligible conversation levels. Compliance with RLR limits is often part of terminal type approval and certification processes to guarantee a minimum quality of service and interoperability across the global network.

Purpose & Motivation

RLR exists to provide an objective, quantifiable measure of a critical aspect of voice terminal quality: how loud the earpiece sounds to the user. Before standardized loudness ratings, terminal acoustics varied widely, leading to inconsistent user experiences where some phones were too quiet, and others were too loud, potentially causing discomfort or hearing damage. The concept of Loudness Ratings was developed to manage the end-to-end loudness of telephone connections, ensuring intelligibility and comfort. RLR specifically addresses the receiving side, allowing engineers to design terminals and networks to meet specific loudness targets (e.g., an OLR of around 10 dB for a good connection). It solves the problem of subjective evaluation by providing a repeatable laboratory measurement that correlates with perceived loudness. Its creation was motivated by the need for interoperability in the global telecommunications network, where devices from different manufacturers connect over networks with varying losses. By defining RLR, standards bodies enabled the predictable engineering of voice quality, which is essential for user satisfaction and effective communication, especially in noisy environments.