ITU-T - P.56
(Pre-Published) Objective measurement of active speech level
|Publication Date:||1 December 2011|
The ITU-T considers it important that there should be a standardized method of objectively measuring speech level, so that measurements made by different organizations may be directly comparable. Requirements of such a meter are that it should measure active speech level and should be independent of operator interpretation.
In this Recommendation, a meter is a complete unit that includes the input circuitry, filter (if necessary), processor and display. The processor includes the algorithm of the detection method.
This meter can safely be used for laboratory experiments or can be used with care on operational circuits.
The method described herein maintains maximum comparability and continuity with past work, provided suitable monitoring is used, e.g. an operator performing the monitoring function. In particular, the new method yields data and conclusions compatible with those that have established the conventional value (22 microwatts) of speech power at the input to the 4-wire point of the international circuit according to Recommendation G.223. A method using operator monitoring can be found in Annex A.
This Recommendation describes a method that can be easily implemented. It also acts as a reference against which other methods can be compared. The purpose of this Recommendation is not to exclude any other method but to ensure that results from different methods give the same result.
Active speech level shall be measured and reported in decibels relative to a stated reference according to the methods described below, namely:
- Method A - Measuring a quantity called speech volume, used for the purpose of real-time control of speech level (see clause 4);
- Method B - Measuring a quantity called active speech level, used for other purposes (see clause 5).
Comparison of readings given by meters of methods A and B can be found in the Handbook on Telephonometry.
In the 2011 revision of the Recommendation Annex B has been added providing the necessary information on how to use the active speech level meter for super-wideband (SWB) signals.
NOTE - This meter cannot be used to determine peak levels but sufficient information exists giving the instantaneous peak/rms ratio, provided the signal has not been restricted or modified in any way, e.g. peak clipping.