PCM5121规格书上备注的：2Vrms FS (0dB) or 1Vrms FS (-6dB)，意思是2Vrms=0dB，1Vrns=-6dB吗。
是否可以提供下换算公式
8.3.5.5 Analog Gain Control
Analog gain control can be selected between 2-Vrms FS (0dB) or 1-Vrms FS (–6 dB). Gain is controlled through hardware by the AGNS pin, and through software (SPI/I2C), Page 1, Register 2, D4(L-ch) / D0(R-ch)
