Monaural selection refers to the selection of only one hearing aid. The side effects are shadow effect and hearing deprivation effect. The shadow effect is due to the high-frequency attenuation of the voice from the side of the non hearing aid ear due to the skull barrier, resulting in the signal-to-noise ratio difference between the two ears as much as 13dB; The effect of hearing deprivation is caused by long-term monaural hearing aid, and the unaided ear gradually loses speech resolution. Therefore, binaural selection is advocated, that is, both ears should be equipped with hearing aids. When hearing aids are used in both ears, the direction of sound source can be judged, the range of hearing can be expanded obviously, and the speech intelligibility in noisy environment can be improved. The more severe the hearing loss, the more important the binaural matching is. In general, binaural selection is recommended as long as there is no contraindication for binaural hearing loss. Binaural selection has many advantages

1) The bilateral hearing is balanced;

2) It can judge the direction of sound source;

3) With the increase of SNR, speech intelligibility will be improved;

4) For example, sitting in a car, if you want to hear the driver's voice, but don't want to hear the noise in the street, you can turn off the hearing aid on the side facing the street;

5) When walking, the sense of balance will be enhanced. If wearing one ear, people tend to walk on the side with good hearing.