scope:

The modulated noise reference unit (MNRU) is a standalone unit that is intended to introduce controlled degradations to speech signals. The purpose of this Recommendation is to describe MNRU as completely and in as much detail as possible to minimize implementation differences that may lead to subjective test results differences.

The need for systems that introduce controlled degradations to speech signals has proven critical for subjective testing, providing consistent reference points for comparison of subjective test results.

It is recommended:

1) that a narrow-band MNRU be used as the reference system in terms of which subjective performance of telephone bandwidth digital processes are expressed;

2) that a wideband MNRU be used as the reference system in terms of which subjective performance of wideband digital processes are expressed;

3) that a fullband MNRU be used as the reference system in terms of which subjective performance of super-wideband or higher digital processes are expressed.

This Recommendation describes narrowband (100-3 400 Hz) and wideband (70-7 000 Hz) MNRU in their analogue and digital forms. Fullband MNRU is specified in digital implementation only.