Reading and playing back audio samples realtime

[tacriela]

Dear fellow forummembers,

For a school project, I would like to get a bass-amplifier up-and-running with an ESP32. My idea for doing this is as follows:
I want to sample audio from AUX via I2S reading. Then I want to filter out the bass frequencies via a low-pass-filter. Next I will add a multiple of these frequency values to the original sample, and I will output them once again via I2S. I think I have the reading part down, however, I'm kind of stuck on writing with I2S. My code is as follows:

Code: [Select all] [Expand/Collapse]

1. // Global defines
2. #define SERIAL_BAUDRATE 9600
3.  
4. // I2S variables
5. #define ARRAYSIZE(a) (sizeof(a) / sizeof(a[0]))       // Set the array size for the samples
6. #define ADC_INPUT_PIN ADC1_CHANNEL_4                  // Pin we want to input from, this is pin 32
7. #define ADC_OUTPUT_PIN ADC1_CHANNEL_5                 // Pin we want to output to, this is pin 33
8. const i2s_port_t I2S_PORT = I2S_NUM_0;                // I2S port used (we use I2S_NUM_0 because this supports ADC and DAC)
9. const double SAMPLING_FREQUENCY = 41000;              // Sampling frequency
10. const int SAMPLE_BLOCK = 512;                         // Amount of samples we want to store in one block
11. const uint16_t OFFSET = (int)ADC_INPUT_PIN * 0x1000;  // Offset for the input pin
12.  
13. // Setup part
14. I2SManager::I2SManager() {
15.   Serial.println("Configuring I2S...");
16.   esp_err_t err;
17.  
18.   // The I2S configuration
19.   const i2s_config_t i2s_config = {
20.     .mode = i2s_mode_t(I2S_MODE_MASTER | I2S_MODE_RX | I2S_MODE_TX | I2S_MODE_ADC_BUILT_IN),
21.     .sample_rate = SAMPLING_FREQUENCY,
22.     .bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,
23.     .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
24.     .communication_format = I2S_COMM_FORMAT_I2S_MSB,
25.     .intr_alloc_flags = ESP_INTR_FLAG_LEVEL1,
26.     .dma_buf_count = 4,
27.     .dma_buf_len = SAMPLE_BLOCK
28.   };
29.  
30.   // Set the driver for the I2S port
31.   err = i2s_driver_install(I2S_NUM_0, &i2s_config, 0, NULL);
32.   if (err != ESP_OK) {
33.     Serial.printf("Failed installing driver: %d\n", err);
34.     while (true)
35.       ;
36.   }
37.  
38.   static const i2s_pin_config_t pin_config = {
39.     .bck_io_num = -1,
40.     .ws_io_num = -1,
41.     .data_out_num = ADC_OUTPUT_PIN,
42.     .data_in_num = ADC_INPUT_PIN
43.   };
44.  
45.   // Set pin config
46.   i2s_set_pin(I2S_PORT, &pin_config);
47.  
48.   // Enable DAC mode
49.   i2s_set_dac_mode(I2S_DAC_CHANNEL_BOTH_EN);
50.  
51.   // Set input pin to ADC mode
52.   err = i2s_set_adc_mode(ADC_UNIT_1, ADC_INPUT_PIN);
53.   if (err != ESP_OK) {
54.     Serial.printf("Failed setting up adc mode: %d\n", err);
55.     while (true)
56.       ;
57.   }
58.  
59.   Serial.println("I2S driver installed.");
60. }
61.  
62. // Loop part
63. void I2SManager::getSamples() {
64.   // Read samples from I2S buffer
65.   size_t bytesRead = 0;
66.   i2s_read(I2S_PORT, (void*)samples, sizeof(samples), &bytesRead, portMAX_DELAY);
67.  
68.   // Check if all samples are filled
69.   if (bytesRead != sizeof(samples)) {
70.     Serial.printf("Could only read %u bytes of %u in FillBufferI2S()\n", bytesRead, sizeof(samples));
71.     return;
72.   }
73.  
74.   // This prints some data, I don't know if its correct because I can't check it yet
75.   for (uint16_t i = 0; i < ARRAYSIZE(samples); i++) {
76.     Serial.printf("%7d\n", samples[i]);
77.   }
78.  
79.   int bytesWritten;
80.   i2s_write(I2S_PORT, (void*)samples, sizeof(samples), (size_t*)&bytesWritten, portMAX_DELAY);
81. }

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If anyone is able to help me that would be very much appreciated. If you have any questions for me, do not hesitate to ask, I'll be monitoring this post as much as I can .

Thanks in advance and kind regards,

Thom