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Table 1 Scale of signal distortion, background intrusiveness and overall quality

From: A modified Wiener filtering method combined with wavelet thresholding multitaper spectrum for speech enhancement

Scale of signal distortion Scale of background intrusiveness Scale of overall quality
5- very natural, no degradation 5- not noticeable 5- excellent
4- fairly natural, little degradation 4- somewhat noticeable 4- good
3- somewhat natural, somewhat degraded 3- noticeable but not intrusive 3- fair
2- fairly unnatural, fairly degraded 2- fairly conspicuous, somewhat intrusive 2- poor
1- very unnatural, very degraded 1- very conspicuous, very intrusive 1- bad