{"id":1941,"date":"2020-09-28T08:39:04","date_gmt":"2020-09-28T06:39:04","guid":{"rendered":"https:\/\/www.pschatzmann.ch\/home\/?p=1941"},"modified":"2022-08-27T21:00:42","modified_gmt":"2022-08-27T19:00:42","slug":"the-synthesis-toolkit-skt-library-for-the-arduino-esp32-midi","status":"publish","type":"post","link":"https:\/\/www.pschatzmann.ch\/home\/2020\/09\/28\/the-synthesis-toolkit-skt-library-for-the-arduino-esp32-midi\/","title":{"rendered":"The Synthesis ToolKit (STK) Library for the Arduino ESP32 – Supporting MIDI and BLE"},"content":{"rendered":"

I made the Synthesis ToolKit (SKT)<\/a><\/strong> available as Arduino Library<\/strong><\/a>.<\/p>\n

The Synthesis ToolKit in C++ (STK) is a set of open source audio signal processing and algorithmic synthesis classes written in the C++ programming language. STK was designed to facilitate rapid development of music synthesis and audio processing software, with an emphasis on cross-platform functionality, realtime control, ease of use, and educational example code.<\/p>\n

Standard STK uses Skini<\/strong> instead of MIDI<\/strong>. This is a simple text based format which provides the same functionality as MIDI.<\/p>\n

However, my intention was to use a simple MIDI keyboard<\/strong> as input device to generate music on an ESP32. In my initial use case I just wanted to connect the device via Bluetooth Low Energy (BLE)<\/strong>.<\/p>\n

After having implemented a BLE server<\/strong> that was able to receive<\/strong> MIDI messages (which was the difficult part) I decided to add some sending<\/strong> functionality as well (which was pretty easy) – and having all this functionality it was no effort at all to refactor the code a little bit to provide additional communication<\/strong> possibilities.<\/p>\n

I have integrated the MIDI functionality into the library:<\/p>\n

Sending MIDI Messages<\/h2>\n

Midi messages can be sent by using the following methods on an output device<\/p>\n

    \n
  • void noteOn(uint8_t note, uint8_t velocity, int8_t channel=-1);<\/li>\n
  • void noteOff(uint8_t note, uint8_t velocity, int8_t channel=-1);<\/li>\n
  • void pitchBend(uint16_t value, int8_t channel=-1);<\/li>\n
  • void channelPressure(uint8_t value, int8_t channel=-1);<\/li>\n
  • void polyPressure(uint8_t valuePar, int8_t channel=-1);<\/li>\n
  • void programChange(uint8_t program, int8_t channel=-1);<\/li>\n
  • void allNotesOff( int8_t channel=-1);<\/li>\n
  • void resetAllControllers( int8_t channel=-1);<\/li>\n
  • void localControl( bool active, int8_t channel=-1);<\/li>\n
  • void controlChange(uint8_t msg, uint8_t value, int8_t channel=-1);<\/li>\n<\/ul>\n

    Output MIDI Messages to Serial<\/h3>\n

    Output of MIDI messages are done with the help of the ArdMidiStreamOut<\/strong> class. It expects a Stream<\/strong> as argument, which makes it so flexible.<\/p>\n

    Here is the implementation that sends the output to Serial. MIDI is a binary protocol, so you will not see anything meaningful in your Serial Monitor:<\/p>\n

    #include \"ArdMidiStreamOut.h\"\n\nusing namespace stk;\n\nArdMidiStreamOut out(Serial);\nStkFloat note = 64; \/\/ 0 to 128\nStkFloat amplitude = 100; \/\/ 0 to 128\n\nvoid setup() {\n    Serial.begin(115200);\n}\n\nvoid loop() {\n    Serial.println();\n    Serial.print(\"playing \");\n    Serial.println(++note);\n\n    out.noteOn( note, amplitude );\n    delay(900);\n    out.noteOff( note, 20 );\n    delay(200);\n    if (note>=90) {\n      note = 30;\n    }\n}\n<\/code><\/pre>\n
    Output MIDI Messages to IP<\/h3>\n
    In order to do communication with TCP\/IP you can use the standard Arduino WiFiClient<\/strong> class. Of cause you need to have a listening server on the receiving side for this to work:<\/p>\n
    #include <WiFi.h>\n#include <WiFiMulti.h>\n#include \"ArdMidiStreamOut.h\"\n\nusing namespace stk;\n\nIPAddress ip(192, 168, 1, 35);\nint port = 9999;\nWiFiClient client;\nArdMidiStreamOut out(client);\nconst char *SSID = \"your ssid\";\nconst char *PWD = \"your password\";\n\nStkFloat note = 64; \/\/ 0 to 128\nStkFloat amplitude = 100; \/\/ 0 to 128\n\nvoid setup() {\n  Serial.begin(115200);\n  WiFi.begin(SSID, PWD);\n  while (WiFi.status() != WL_CONNECTED) {\n    Serial.print('.');\n    delay(1000);\n  }\n\n  Serial.print(\"Connected to IP address: \");\n  Serial.println(WiFi.localIP());\n\n  client.connect(ip, port);\n}\n\nvoid loop() {\n    Serial.print(\"playing \");\n    Serial.println(++note);\n\n    out.noteOn( note, amplitude );\n    delay(900);\n    out.noteOff( note, 20 );\n    delay(200);\n    if (note>=90) {\n      note = 30;\n    }\n}\n<\/code><\/pre>\n
    We need to login into WIFI and then connect to the requested IP address and port. This is just plain vanilla Arduino code. Since we have given the WifiClient as argument to the ArdMidiStreamOut<\/strong> class, the information is automatically sent to the expected destination.<\/p>\n
    Output MIDI Messages to UDP<\/h3>\n
    We have already seen an example in the introduction on how to send out sound via UDP. This is very similar and we use ArdMidiStreamOut<\/strong> instead of ArdStreamBinaryOut.<\/p>\n
    #include \"WiFi.h\" \n#include \"ArdUdp.h\" \n#include \"ArdMidiStreamOut.h\"\n\nusing namespace stk;\n\nIPAddress ip(192, 168, 1, 35);\nArdUdp udp(ip, 7000);\nArdMidiStreamOut out(udp);\nconst char *SSID = \"your ssid\";\nconst char *PWD = \"your password\";\n\nStkFloat note = 64; \/\/ 0 to 128\nStkFloat amplitude = 100; \/\/ 0 to 128\n\nvoid setup() {\n  Serial.begin(115200);\n  WiFi.begin(SSID, PWD);\n  while (WiFi.status() != WL_CONNECTED) {\n    Serial.print('.');\n    delay(1000);\n  }\n\n  Serial.print(\"Connected to IP address: \");\n  Serial.println(WiFi.localIP());\n}\n\nvoid loop() {\n    Serial.print(\"playing \");\n    Serial.println(++note);\n\n    out.noteOn( note, amplitude );\n    delay(900);\n    out.noteOff( note, 20 );\n    delay(200);\n    if (note>=90) {\n      note = 30;\n    }\n}\n<\/code><\/pre>\n
    Receiving MIDI Messages<\/h2>\n
    Receiving messages is easy as well. You use the class ArdMidiStreamIn<\/strong> together with a Stream and a ArdMidiEventHandler<\/strong> which implements the parsing of MIDI messages.<\/p>\n
    Input MIDI Messages from Serial<\/h3>\n
    #include \"Voicer.h\"\n#include \"Clarinet.h\"\n#include \"ArdMidiStreamIn.h\"\n\nusing namespace stk;\n\nVoicer voicer;\nClarinet clarinet(440);\nArdMidiEventHandler handler(&voicer);\nArdMidiStreamIn in(Serial, handler);\n\nvoid setup() {\n  Serial.begin(115200);\n  voicer.addInstrument(&clarinet);\n}\n\nvoid loop() {\n  in.loop();\n}\n\n\n<\/code><\/pre>\n
    In the setup method we tell the voicer to play the clarinet when we receive a corresponding command on channel 0.
    \nIn the loop we need to call the loop() method from the ArdMidiStreamIn to trigger the receiving and parsing of the MIDI messages.<\/p>\n
    Input MIDI Messages from UDP<\/h3>\n
    We can use the same logic as above, but we provide the standard Arduino WiFiUDP<\/strong> to the ArdMidiStreamIn<\/strong>:<\/p>\n
    #include <WiFi.h>\n#include <WiFiClient.h>\n#include <WiFiUdp.h>\n#include <ArdMidiStreamIn.h>\n#include \"Voicer.h\"\n#include \"Clarinet.h\"\n\nusing namespace stk;\n\n\nWiFiUDP udp;\nClarinet clarinet(440);\nVoicer voicer;\nArdMidiEventHandler handler(&voicer);\nArdMidiStreamIn in(udp, handler );\nint localPort = 9000;\n\nvoid setup() {\n  Serial.begin(115200);\n  WiFi.begin(SSID, PWD);\n  while (WiFi.status() != WL_CONNECTED) {\n    Serial.print('.');\n    delay(1000);\n  }\n\n  Serial.print(\"Connected to IP address: \");\n  Serial.println(WiFi.localIP());  \n\n  voicer.addInstrument(&clarinet,0);\n  udp.begin(localPort);\n}\n\nvoid loop() {\n  in.loop();\n}\n\n<\/code><\/pre>\n
    BLE Server<\/h2>\n
    The MIDI BLE Server functionality is provided by the ArdMidiBleServer<\/strong> class. Above you have already seen all relevant components and how they work together.<\/p>\n
    Sending of MIDI Messages over BLE<\/h3>\n
    #include <ArdMidiBleServer.h>\n\nusing namespace stk;\n\nArdMidiBleServer ble(\"MidiServer\");\n\nStkFloat note = 64; \/\/ 0 to 128\nStkFloat amplitude = 100; \/\/ 0 to 128\n\nvoid setup() {\n  Serial.begin(115200);\n  ble.start();\n}\n\nvoid loop() {\n  Serial.print(\"playing \");\n  Serial.println(++note);\n\n  ble.noteOn( note, amplitude );\n  delay(900);\n  ble.noteOff( note, 20 );\n  delay(200);\n  if (note>=90) {\n    note = 30;\n  }\n}\n\n<\/code><\/pre>\n
    Receiving of MIDI Messages over BLE<\/h3>\n
    In order to receive an process inbound MIDI messages we use the ArdMidiBLEEventHandler<\/strong> class which expects a voicer.<\/p>\n
    #include <Voicer.h>\n#include <Clarinet.h>\n#include <ArdMidiBleEventHandler.h>\n#include <ArdMidiBleServer.h>\n\nusing namespace stk;\n\nVoicer voicer;\nClarinet clarinet(440);\nArdMidiBleEventHandler handler(&voicer);\nArdMidiBleServer ble(\"MidiServer\", &handler);\n\nvoid setup() {\n  Serial.begin(115200);\n  voicer.addInstrument(&clarinet, 0);\n  ble.start(voicer);\n}\n\nvoid loop() {\n}\n\n<\/code><\/pre>\n
    Of cause you could add the loop processing from the sending example here as well and you would have a MIDI BLE server that can send and receive MIDI messages at the same time!<\/p>\n
    BLE Client<\/h2>\n
    After having seen how to use the BLE Server I finally demonstrate the corresponding ArdMidiBleClient<\/strong> class which acts as BLE Client.
    \nLike the server it can receive and send out MIDI messages at the same time:<\/p>\n
    #include <Voicer.h>\n#include <Clarinet.h>\n#include <ArdMidiBleEventHandler.h>\n#include <ArdMidiBleServer.h>\n\nusing namespace stk;\n\nVoicer voicer;\nClarinet clarinet(440);\nArdMidiBleEventHandler handler(&voicer);\nArdMidiBleServer ble(\"MidiServer\", &handler);\n\nvoid setup() {\n  Serial.begin(115200);\n  voicer.addInstrument(&clarinet, 0);\n  ble.start(voicer);\n}\n\nStkFloat note = 64; \/\/ 0 to 128\nStkFloat amplitude = 100; \/\/ 0 to 128\n\nvoid loop() {\n  Serial.print(\"playing \");\n  Serial.println(++note);\n\n  ble.noteOn( note, amplitude );\n  delay(900);\n  ble.noteOff( note, 20 );\n  delay(200);\n  if (note>=90) {\n    note = 30;\n  }\n}\n\n<\/code><\/pre>\n
    In this example we receive and process MIDI messages on channel 0 and send out messages on channel 1.<\/p>\n
    Conclusion<\/h2>\n
    We can receive and process MIDI messages over different communication channels – including BLE. Combining this with the standard sound generation functionality of the STK framework we can now build some powerful Music Projects quite easily<\/strong>!<\/p>\n
    And if you discover that one of the provided Classes does not quite meet your exact requirements: This is C++ – you can just create a Subclass and overwrite the method that you want to extend…<\/p>\n","protected":false},"excerpt":{"rendered":"
    I made the Synthesis ToolKit (SKT) available as Arduino Library. The Synthesis ToolKit in C++ (STK) is a set of open source audio signal processing and algorithmic synthesis classes written in the C++ programming language. 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