Algorithms for a system which performs in-service nonintrusive measurements
of telephone line parameters such as echo path delay, echo attenuation, sp
eech and noise levels are presented in this paper, It forms the theoretical
background of a hardware implementation of the ITU-T P.561 recommendations
for nonintrusive assessment of quality of a telephone network for voice tr
ansmissions. The type of input signal to the echo path, whether it is speec
h, fax, or data, has to be determined during the measurement procedure.
In the system, the relevant parameters are estimated by means of frequency-
domain block-processing algorithms and the estimation process is controlled
by algorithms monitoring the signal flow. The complexity of the echo path
estimation algorithm is determined and compared to a standard procedure bas
ed on the adaptive normalized least mean square (NMLS) algorithm.
Simulations showing the performance of the system in single- and double-tal
k situations are presented. Examples of results from the hardware real-time
implementation operating on an international connection are also shown.