单音调低音 meaning in English

one-tone bass

The calls of non - passerine are some kinds of monotonous dull vocalizations with the characteristics of low and deep frequency , single syllable , low basic frequency and with no ability of modulation in frequency and amplitude . most of the calls are monotonous and low quality mainly based on the basic song . compare the vocal of sub - oscine passerine with non - passerine , they have some similar aspects , but the former possesses of stronger capability of vocal control
非鸣禽的叫声低沉而单调，音节种类单一，基本音频率低，缺乏频率调制以及幅度调制的能力，叫声的品质因数很低，不悦耳，大多为以基本音为主的单音调低音品叫声，亚鸣禽的叫声与非鸣禽近似，但在控声能力方面又有所提高。