7 Performance Objectives assessed by Objective Measures

06.773GPPMinimum Performance Requirements for Noise Suppresser Application to the AMR Speech EncoderTS

7.1 Impact on Active Speech Level

The AMR speech codec with noise suppression activated must not significantly alter the active speech level.

The requirement is checked with the use of a P.56 speech level meter (the use of which remains for further study). Let x be the averaged level of the clean speech material for one experiment and let y be the averaged level of the processed material with AMR NS activated for the same experiment. The requirement is met if the absolute difference between x and y is less than 2 dB for all experiments. The processed material should not be normalised to the nominal speech level before the listening tests.

Note that this requirement does not preclude the use of active level control.

7.2 Objective Speech Quality Measures

The objective measures of noise power level reduction (NPLR) and signal-to-noise ratio improvement (SNRI) defined in Annex 1 are to be used to characterise the performance of the AMR/NS solution. Objectives are defined for these measures in the following table. These measures will be used to provide additional information only and are not to be considered to be requirements.

C source code is attached to this specification which shall be used to undertake these measurements.

Objective quality measure/test condition

Performance objective

NPLR

Assessment: To be evaluated using a predefined set of material (as used in the AMR/NS Selection Phase) comprising speech mixed with stationary car noise in the SNR conditions of 6 dB and 15 dB, following otherwise the guidelines set forth in [Annex 1].

–7 dB or lower

SNRI

Assessment: To be evaluated using a predefined set of material (as used in the AMR/NS Selection Phase) comprising speech mixed with stationary car noise in the SNR conditions of 6 dB and 15 dB, following otherwise the guidelines set forth in [Annex 1].

6 dB or higher