Bluetooth with DSP and Internal DAC

[InsaneEngineer]

I want to some research limits of ESP32 in audio processing. But i dont have external DAC. I am override a callback function, but original code of this function very hard to understand:

                if (is_i2s_output) {
		// special case for internal DAC output, the incomming PCM buffer needs
		// to be converted from signed 16bit to unsigned
		int16_t* data16 = (int16_t*)data;

		if (this->i2s_config.mode & I2S_MODE_DAC_BUILT_IN) {
			//HACK: this is here to remove the const restriction to replace the data in place as per
			//https://github.com/espressif/esp-idf/blob/178b122/components/bt/host/bluedroid/api/include/api/esp_a2dp_api.h
			//the buffer is anyway static block of memory possibly overwritten by next incomming data.

			for (int i = 0; i < len / 2; i++) {
				int16_t sample = data[i * 2] | data[i * 2 + 1] << 8;
				data16[i] = sample + 0x8000;
			}
		}

P.s. I had some knowledge in therory of Digital Filters and my main object - it iss creating some sort of equalizer. For first attempt i am creating a simple digital low pass filter:

[pschatzmann]

I suggest that you have a look at my AudioTools library where you don't need to bother about these details.
Here is an example using an Equilizer. Just change the AudioKitStream to an AnalogAudioStream to use the internal DAC.

If you use the internal DAC with the ESP-IDF API, bits_per_sample is 16 but the DAC module will only take the 8bits from MSB.