4.3.2. Subjective Evaluation

To compare the subjective quality of the enhanced speech by baseline and proposed methods, we conducted two pairs of AB preference tests: AECNN versus the progressive generator and SERGAN versus the progressive generator with the multi-scale discriminator. Two speech in each pair were given in arbitrary order. For each listening test, 14 listeners participated, and 50 pairs of the speech were randomly selected. Listeners could listen to the speech pairs as many times as they wanted and were instructed to choose the speech with better perceptual quality. If the quality of the two samples was indistinguishable, listeners could select no preference.

#### **5. Experiments and Results**

In order to investigate the individual effect of the proposed generator and discriminator, we experimented on the progressive generator with and without the multi-scale discriminator. Furthermore, we plotted *L*1 losses at each layer *<sup>L</sup>*1(*Gn*) to show that the proposed model makes training fast and stable. Finally, the performance of the proposed model is compared with that of the other GAN-based speech enhancement techniques.

#### *5.1. Performance of Progressive Generator*
