Hi Coleman,
With your help, it works now. Thank a lot!
However, the overall output level from mic is not large enough, even though I had boosted the micbias to highest and the mic input stage gain to 6 dB, this did not help much...overall situation is, the stereo audio input from the IN 3/4 is quite larger than from mic. I tried two different analog mics, the same situation...I cannot accept current audio quality from the mic1 and mic2 (volume up the final playback stage did not help...it only raise the noise...)
As I will have to have two mics to operate in the same time in parallel with stereo audio input from IN 3/4 (and all need to go to dsp core for digital processing), my questions then are:
1. What can the possible problem is? What place should I check?
2. Can I change the micbias pull up resistors (R7 and R15 on the schematics) to a lower value, such as 1K, to boost the mic level? but without hurting this audio codec chip?
3. Or, I need to find better (or matching ) mic such that they work with the existing circuits? Can you make some suggestion to the selections of such good MEM analog mics that work with ADAU1761Z?
4. Does ADAU1761Z support two digital mics that I can separately adjust with? "Figure 32. Record Signal Path" of the ADAU1761Z.pdf seems to suggest that when digital mic is used, the LAUX / RAUX cannot be used through dsp core any more?
Thanks in advance!
Kelvin