TI's Development Board uses the aic23b audio decoding chip, which has two input ports, mic in and line in. Now we use the sharc 21479 version of Adi, which uses the 1939 chip of Adi, but 1939 does not provide mic in and line in input differentiation. However, the audio port of the Development Board can only receive linear input, the mic in cannot be received, which is very depressing. The next step is to make a small board for converting the mic in to the line in.
I found many differences between line in and MIC in on the Internet. Simply put, line in is directly input into the chip, because the line in signal is loaded with voltage, not a natural signal. However, when using mic in as the input of the chip, you also need to add a front-amplifier, because mic in does not have voltage at the input, such as using a common microphone, it has no voltage output, and must be connected to the device and provided by the device. Generally, the output signal of a microphone is only 1 mV.