Investigating the AI Thinker AudioKit Audio Input Bug…

In my last blog, I have described how to process audio input data and encountered the bug that the microphone and line input are mixed together and that there is an open issue for this which has been open for quite some time now.

So I decided to do a little bit of research for my ESP32 AudioKit V2.2 3478 :

First Assumption: The Registers are not set up correctly

The ES8388 Data Sheet describes in Register 10:

• Input1 the register values 4:5 and 7:6 must be 00
• Input2 the register values 4:5 and 7:6 must be 01

The value 10 is reserved and the value 11 is used for differential input.

So the next step is to determine the current register setting:

#include "AudioTools.h"
#include "AudioLibs/AudioKit.h"
#include "Wire.h"

using namespace audio_tools;  

AudioKitStream kit; // Access I2S as stream

void readRegister(int addr, int reg){
    Wire.begin(I2C_MASTER_SDA_IO, I2C_MASTER_SCL_IO);
    Wire.beginTransmission(addr >> 1);
    Wire.write(reg);
    int rc = Wire.endTransmission();

    uint8_t result_len = Wire.requestFrom((uint16_t)(addr >> 1), (uint8_t)1, true);
    if (result_len > 0) {
        byte result = Wire.read();
        Serial.print(reg);
        Serial.print("/0x");
        Serial.print(reg,HEX);
        Serial.print(" : ");
        Serial.print(result,HEX);
    } 
}

void dumpRegisters(){
    for (int j=0;j<53;j++){
      readRegister(ES8388_ADDR,j);
    }  
}

// Arduino Setup
void setup(void) {
    Serial.begin(115200);
    AudioLogger::instance().begin(Serial, AudioLogger::Info);

    // setup kit
    auto cfg = kit.defaultConfig(RXTX_MODE);
    cfg.input_device = AUDIO_HAL_ADC_INPUT_LINE2;
    kit.begin(cfg);

    // dump all registers
    dumpRegisters();
}

// Arduino loop - copy data
void loop() {
}

Executing the sketch gives the following results

0/0x0 : 12
1/0x1 : 50
2/0x2 : 0
3/0x3 : 0
4/0x4 : 3C
5/0x5 : 0
6/0x6 : 0
7/0x7 : 7C
8/0x8 : 0
9/0x9 : BB
10/0xA : 50
11/0xB : 2
12/0xC : C
13/0xD : 2
14/0xE : 30
15/0xF : 20
16/0x10 : 0
17/0x11 : 0
18/0x12 : 38
19/0x13 : B0
20/0x14 : 32
21/0x15 : 6
22/0x16 : 0
23/0x17 : 18
24/0x18 : 2
25/0x19 : 0
26/0x1A : 0
27/0x1B : 0
28/0x1C : 8
29/0x1D : 0
30/0x1E : 1F
31/0x1F : F7
32/0x20 : FD
33/0x21 : FF
34/0x22 : 1F
35/0x23 : F7
36/0x24 : FD
37/0x25 : FF
38/0x26 : 0
39/0x27 : 90
40/0x28 : 28
41/0x29 : 28
42/0x2A : 90
43/0x2B : 80
44/0x2C : 0
45/0x2D : 0
46/0x2E : D
47/0x2F : D
48/0x30 : 0
49/0x31 : 0
50/0x32 : 0
51/0x33 : AA
52/0x34 : AA

For Register 10 I am getting
AUDIO_HAL_ADC_INPUT_LINE1: “A:0” – hex 00 gives 0b00000000
AUDIO_HAL_ADC_INPUT_LINE2: “A:50” – hex 50 gives 0b01010000

This looks correct and this assumption did turn out to be false. The strange thing however is that I dont get any input with AUDIO_HAL_ADC_INPUT_LINE1 and with AUDIO_HAL_ADC_INPUT_LINE2, I get both the Microphone and the Line IN!

Second Assumption: The Board Design is routing the signals to the wrong pins

Here are the pins for the ES8388:

• Linein should go only to LINEINL and LINEINR
• Microphone input should go only to MIC1P and MIC1N and MIC2P and MIC2N

Fortunately the wiring schema has been published: This looks OK as well: The Mic pins are routed to the mic inputs and the line input is also ending up at the right pins.

Third Assumption: The Board is routing the signals to the wrong pins

I will have to test this with an Oscilloscope. I tapping on the microphones and tried to determine if I see any impact on line in.
But no – this does not seem to be the case.

Forth Assumption: The Mixer is configured to provide the microphone input

This would be managed via register 39 – bit 6!
Register 39 has 0x90 which is 0b10010000 – and bit 6 is switched off.
Assumption busted!

Help !!! I am running out of options now…