音频codec中的Sidetone Insertion有什么作用，看了不是很明白，哪位大侠帮忙具体解释一下吧
Sidetone Insertion
The TLV320AIC23B has a sidetone insertion made where the microphone input is routed to the line and headphone outputs. This is useful for telephony and headset applications. The attenuation of the sidetone signal may be set to −6 dB, −9 dB, −12 dB, −15 dB, or 0dB, by software selection (see Section 3.1.3). If this mode is used to sum the microphone input with the DAC output and line inputs, care must be taken not to exceed signal level to avoid clipping and distortion.
