ESP32 - Reading and playing back audio samples realtime (with I2S) - arduino

Question

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:
// Global defines
#define SERIAL_BAUDRATE 9600
// I2S variables
#define ARRAYSIZE(a) (sizeof(a) / sizeof(a[0])) // Set the array size for the samples
#define ADC_INPUT_PIN ADC1_CHANNEL_4 // Pin we want to input from, this is pin 32
#define ADC_OUTPUT_PIN ADC1_CHANNEL_5 // Pin we want to output to, this is pin 33
const i2s_port_t I2S_PORT = I2S_NUM_0; // I2S port used (we use I2S_NUM_0 because this supports ADC and DAC)
const double SAMPLING_FREQUENCY = 41000; // Sampling frequency
const int SAMPLE_BLOCK = 512; // Amount of samples we want to store in one block
const uint16_t OFFSET = (int)ADC_INPUT_PIN * 0x1000; // Offset for the input pin
// Setup part
I2SManager::I2SManager() {
Serial.println("Configuring I2S...");
esp_err_t err;
// The I2S configuration
const i2s_config_t i2s_config = {
.mode = i2s_mode_t(I2S_MODE_MASTER | I2S_MODE_RX | I2S_MODE_TX | I2S_MODE_ADC_BUILT_IN),
.sample_rate = SAMPLING_FREQUENCY,
.bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,
.channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
.communication_format = I2S_COMM_FORMAT_I2S_MSB,
.intr_alloc_flags = ESP_INTR_FLAG_LEVEL1,
.dma_buf_count = 4,
.dma_buf_len = SAMPLE_BLOCK
};
// Set the driver for the I2S port
err = i2s_driver_install(I2S_NUM_0, &i2s_config, 0, NULL);
if (err != ESP_OK) {
Serial.printf("Failed installing driver: %d\n", err);
while (true)
;
}
static const i2s_pin_config_t pin_config = {
.bck_io_num = -1,
.ws_io_num = -1,
.data_out_num = ADC_OUTPUT_PIN,
.data_in_num = ADC_INPUT_PIN
};
// Set pin config
i2s_set_pin(I2S_PORT, &pin_config);
// Enable DAC mode
i2s_set_dac_mode(I2S_DAC_CHANNEL_BOTH_EN);
// Set input pin to ADC mode
err = i2s_set_adc_mode(ADC_UNIT_1, ADC_INPUT_PIN);
if (err != ESP_OK) {
Serial.printf("Failed setting up adc mode: %d\n", err);
while (true)
;
}
Serial.println("I2S driver installed.");
}
// Loop part
void I2SManager::getSamples() {
// Read samples from I2S buffer
size_t bytesRead = 0;
i2s_read(I2S_PORT, (void*)samples, sizeof(samples), &bytesRead, portMAX_DELAY);
// Check if all samples are filled
if (bytesRead != sizeof(samples)) {
Serial.printf("Could only read %u bytes of %u in FillBufferI2S()\n", bytesRead, sizeof(samples));
return;
}
// This prints some data, I don't know if its correct because I can't check it yet
for (uint16_t i = 0; i < ARRAYSIZE(samples); i++) {
Serial.printf("%7d\n", samples[i]);
}
int bytesWritten;
i2s_write(I2S_PORT, (void*)samples, sizeof(samples), (size_t*)&bytesWritten, portMAX_DELAY);
}
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 :).
P.S. I've also uploaded this question to the ESP32 official forum.
Thanks in advance and kind regards,
Thom