I am looking at http://www.restena.lu/convict/Jeunes/PhaseSound.htm .
I see MIC, 2 amplifiers, a peak detector, amplifier and a comparator. R11 & R20 set the lever for the comparator. The audio is above or below the level. The input to the PIC is a 1 or 0.

The PIC measures the delay from left to right. If the sound arrives at the same time then the sound came from directly in front or back. If the right ear hears the sound first then by and amount of delay the sound is to the right at some angle. Sound is 1100 feet/second. If the ears are 1 ft apart and the delay is 1mS then the sound is directly to the side. If the sound is 0.1mS delayed then the sound is only slightly to the side. Do the math.

My first thought is to drop the comparator and run the output of the last amplifier into the ADC of the PIC. The compare function then is done in software. If ADC > 53 then ear=1 else ear=0. The compare value (53) can be automatically adjusted for week/strong signals. There is probably too much delay through the ADC.

Next idea: Keep the comparators and replace R11 + R20 with a DAC. This way software chooses the compare level to match the sound level.

In your case you want to compare the sound “level” to determine left/right. You will want the ears facing left and right not front like the first example. Because you are thinking level not delay, I would drop the hardware comparator. The PIC must have 2 or more analog inputs! You will compare ADC1 and ADC2 and head in the correct direction. You may have trouble knowing if the sound is in front or in back. Worst case you may have to rotate 360 degrees before you know which way to go. I think you will have to go zigzag, drive [walk] +10 degrees then –10 degrees. If the sound is behind not in front you will know! Zigzagging may give you more accurate information.

You will find the audio level range is far greater then you think. (I have done this before.) In the first example the level is not very important, just the delay. The second example the level is all you have. A 8 bit ADC will gave you a maybe 100:1 range in level so about 10:1 range in distance. (10 feet to 1 foot) Not good. By changing the amplifier and adding AGC you could measure 1,000:1 or more. I think I have a PIC measuring audio levels to 10,000:1.

Sounds fun…Good luck.