code:

#define NUM_SAMPLES   512
#define I2S_NUM         (0)

void configure_i2s() {
	i2s_config_t i2s_config =
	{
	.mode = (i2s_mode_t)(I2S_MODE_MASTER | I2S_MODE_RX | I2S_MODE_ADC_BUILT_IN),  // I2S receive mode with ADC
	.sample_rate = 22000,                                           
	.bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,                                 
	.channel_format = I2S_CHANNEL_FMT_ALL_LEFT,                                  
	.communication_format = I2S_COMM_FORMAT_I2S_MSB,// (i2s_comm_format_t)(I2S_COMM_FORMAT_I2S | I2S_COMM_FORMAT_I2S_MSB),   // I2S format
	.intr_alloc_flags = 1,                                                        // none
	.dma_buf_count = 2,                                                           
	.dma_buf_len = NUM_SAMPLES,                                                  
	.use_apll = 0,                                                                // 1 seems to be better for lower frequency signals
	};
	adc1_config_channel_atten(ADC1_CHANNEL_0, ADC_ATTEN_11db);
	adc1_config_width(ADC_WIDTH_12Bit);
	i2s_driver_install(I2S_NUM_0, &i2s_config, 0, NULL);
	 
	i2s_set_adc_mode(ADC_UNIT_1, ADC1_CHANNEL_0);
	SET_PERI_REG_MASK(SYSCON_SARADC_CTRL2_REG, SYSCON_SARADC_SAR1_INV); //invert the adc back to normal
	i2s_adc_enable(I2S_NUM_0);
}

uint16_t i2s_read_buff[NUM_SAMPLES];
SemaphoreHandle_t i2s_sem = NULL;


void adc_read_task(void *parm) {
	while (1) {
		//xSemaphoreTake(i2s_sem, portMAX_DELAY);
		i2s_read_bytes(I2S_NUM_0, i2s_read_buff, NUM_SAMPLES * sizeof(uint16_t), portMAX_DELAY);
		//xSemaphoreGive(i2s_sem);
	}
}

void loop() {
	//xSemaphoreTake(i2s_sem, 1);
	for (int i = 0; i < NUM_SAMPLES; i++) {
		Real[i] = i2s_read_buff[i];
		//Serial.println(i2s_read_buff[i]);
	}
	//xSemaphoreGive(i2s_sem);
}


void setup() {
	configure_i2s();

	vSemaphoreCreateBinary(i2s_sem);
	xSemaphoreGive(i2s_sem);
	xTaskCreate(adc_read_task, "ADC read task", 2048, NULL, 5, NULL);
	Serial.println("Finished setup");
}