ITU-T Recommendation P.810, Modulated Noise Reference Unit (MNRU), 1996

This Recommendation describes the Modulated Noise Reference Unit (MNRU), a standalone unit for introducing controlled degradations to speech signals. As such, the MNRU has been used extensively in subjective performance evaluations of digital processes, both in conventional telephone bandwidth and in wideband (e.g. 70-7000 Hz) applications.
Historically, the MNRU has been implemented in analogue hardware. The revisions encompassed in this version of the Recommendation are the inclusion of descriptions of digital implementations of the MNRU. These descriptions are suitable for implementation in software or on digital hardware. One further revision is to note the need for a high-pass filter (removal of any DC component of the input speech material) for all implementations. Existing analogue hardware implementations of the MNRU will continue to meet the specifications in this Recommendation, provided such filtering is applied externally.