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libraries/audio-tools/examples/examples-stream/streams-sd_mp3-i2s/README.md

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+# SD Player
+
+We just play a mp3 file (using the Arduino SD library) and output the result via I2S to an external DAC. 
+
+An ESP32 was used to test this sketch.
+
+### External DAC:
+
+![DAC](https://pschatzmann.github.io/Resources/img/dac.jpeg)
+
+
+I am just using the default pins defined by the framework. However I could change them with the help of the config object. The mute pin can be defined in the constructor of the I2SStream - by not defining anything we use the default which is GPIO23
+
+DAC  |	ESP32
+-----|----------------
+VCC  |	5V
+GND  |	GND
+BCK  |	BCK (GPIO14)
+DIN  |	OUT (GPIO22)
+LCK  |	BCK (GPIO15)
+FMT  |	GND
+XMT  |	3V (or another GPIO PIN which is set to high)
+
+- DMP - De-emphasis control for 44.1kHz sampling rate(1): Off (Low) / On (High)
+- FLT - Filter select : Normal latency (Low) / Low latency (High)
+- SCL - System clock input (probably SCL on your board).
+- FMT - Audio format selection : I2S (Low) / Left justified (High)
+- XMT - Soft mute control(1): Soft mute (Low) / soft un-mute (High)

libraries/audio-tools/examples/examples-stream/streams-sd_mp3-i2s/streams-sd_mp3-i2s.ino

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+/**
+ * @file streams-sd_mp3-i2s.ino
+ * @author Phil Schatzmann
+ * @brief decode MP3 file and output it on I2S
+ * @version 0.1
+ * @date 2021-96-25
+ * 
+ * @copyright Copyright (c) 2021 
+ */
+
+
+#include <SPI.h>
+#include <SD.h>
+#include "AudioTools.h"
+#include "AudioTools/AudioCodecs/CodecMP3Helix.h"
+
+
+const int chipSelect=10;
+I2SStream i2s; // final output of decoded stream
+EncodedAudioStream decoder(&i2s, new MP3DecoderHelix()); // Decoding stream
+StreamCopy copier; 
+File audioFile;
+
+void setup(){
+  Serial.begin(115200);
+  AudioToolsLogger.begin(Serial, AudioToolsLogLevel::Info);  
+
+  // setup file
+  SD.begin(chipSelect);
+  audioFile = SD.open("/Music/Conquistadores.mp3");
+
+  // setup i2s
+  auto config = i2s.defaultConfig(TX_MODE);
+  i2s.begin(config);
+
+  // setup I2S based on sampling rate provided by decoder
+  decoder.begin();
+
+  // begin copy
+  copier.begin(decoder, audioFile);
+
+}
+
+void loop(){
+  if (!copier.copy()) {
+    stop();
+  }
+}