A.1 Notations

26.0773GPPApplication to the Adaptive Multi-Rate (AMR) speech encoderMinimum performance requirements for Noise SuppresserRelease 17TS

The following notations are used in this document:

– The operator AMR() corresponds to applying the AMR speech encoder and decoder on the input.

– The operator NR() corresponds to applying the NS algorithm, and the AMR speech encoder and decoder on the input.

– The clean speech signals are referred to as s_i , i = 1 to I.

– The noise signals are referred to as n_j , j = 1 to J.

– The noisy speech test signals are referred to as d_ij = _ij(SNR) n_j+ s_i, i = 1 to I, j = 1 to J, where d_ij is built by adding s_i and n_j with a pre-specified SNR as presented below.

– The processed signal are referred to as y_ij = NR (d_ij).

– The reference signal in the calculations shall be either the noisy speech test signal d_ij itself or d_ij processed by the AMR speech codec without NS processing. The latter signal will be referred to as c_ij = AMR (d_ij), i = 1 to I, j = 1 to J. The relevant reference signal will be indicated in the formulation of each objective measure below.

– The notation Log() indicates the decimal logarithm.

– _ij(SNR) is the scaling factor to be applied to the background noise signal n_i in order to have a ratio SNR (in dB) between the clean speech signal s_i and n_j. The scaling of the input speech and noise signals is to be carried according to the following procedure:

1) The clean speech material is scaled to a desired dBov level with the ITU-T Recommendation P.56 [7] speech voltmeter, one file at a time, each file including a sequence of one to four utterances from one speaker.

2) A silence period of 2 s is inserted in the beginning of each of the resulting files to make up augmented clean speech files.

3) Within each noise type and level, a noise sequence is selected for every speech utterance file, each with the same length as the corresponding speech files, and each noise sequence is stored in a separate file.

4) Each of the noise sequences is scaled to a dBov level leading to the SNR condition corresponding to the _ij(SNR) value in each of the test cases by applying the RMS level based scaling according to the P.56 [7] recommendation.

– The determination of which frames contain active speech is to be carried out with reference to the ITU-T Recommendation P.56 [7] active speech level measurement and is related to the classification of the frames into the presented speech power classes which is explained below.