{"id":1853,"date":"2020-09-24T11:17:12","date_gmt":"2020-09-24T09:17:12","guid":{"rendered":"https:\/\/www.pschatzmann.ch\/home\/?p=1853"},"modified":"2021-12-25T15:20:59","modified_gmt":"2021-12-25T14:20:59","slug":"the-synthesis-toolkit-skt-library-for-the-arduino-esp32","status":"publish","type":"post","link":"https:\/\/www.pschatzmann.ch\/home\/2020\/09\/24\/the-synthesis-toolkit-skt-library-for-the-arduino-esp32\/","title":{"rendered":"The Synthesis ToolKit (STK) Library for the Arduino ESP32 – An Introduction"},"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

The information below is based on the original STK tutorial<\/a> but was adapted to cover my extensions for the Arduino environment.<\/p>\n

Introduction<\/h2>\n

Audio and control signals throughout STK use a floating-point data type, StkFloat, the exact precision of which can be controlled via a typedef statement in Stk.h. By default, an StkFloat is a double-precision floating-point value. Thus, the ToolKit can use any normalization scheme desired. The base instruments and algorithms are implemented with a general audio sample dynamic maximum of +\/-1.0.<\/p>\n

In general, the computation and\/or passing of values is performed on a “single-sample” basis. For example, the stk::Noise class outputs random floating-point numbers in the range +\/-1.0. The computation of such values occurs in the stk::Noise::tick() function. The following program will generate 20 random floating-point (StkFloat) values in the range -1.0 to +1.0:<\/p>\n

#include \"Noise.h\"\nusing namespace stk;\n\nvoid setup() {\n  Serial.begin(115200);\n  StkFloat output;\n  Noise noise;\n  for ( unsigned int i=0; i<20; i++ ) {\n    output = noise.tick();\n    Serial.println(output);\n  }\n}\n\nvoid loop() {\n}\n\n<\/code><\/pre>\n
Here is the result in the Arduino Serial Plotter:<\/p>\n
\"\"<\/p>\n
Nearly all STK classes implement tick() functions that take and\/or return sample values. Within the tick() function, the fundamental sample calculations are performed for a given class. Most STK classes consume\/generate a single sample per operation and their tick() method takes\/returns each sample “by value”. In addition, every class implementing a tick() function also provides one or more overloaded tick() functions that can be used for vectorized computations, as shown in the next example.<\/p>\n
#include \"Noise.h\"\nusing namespace stk;\n\nNoise noise;\nStkFrames output(20, 1);   \/\/ initialize StkFrames to 20 frames and 1 channel (default: interleaved)\n\nvoid setup() {\n  Serial.begin(115200);\n}\n\nvoid loop() {\n  noise.tick( output );\n  for ( unsigned int i=0; i<output.size(); i++ ) {\n    Serial.println(output[i]);\n  }\n}\n<\/code><\/pre>\n
The generated output is the same as in the first example.<\/p>\n
Hello Sine! (Input to Output)<\/h2>\n
We’ll continue our introduction to the Synthesis ToolKit with a simple sine-wave oscillator program. STK provides two different classes for sine-wave generation. In STK it is quite common to send the output to a file. In Arduino however we rarely have any file system available but we need usually write output to serial. Here is how it can be done:<\/p>\n

#include \"SineWave.h\"\n#include \"ArdStreamOut.h\"\n\nusing namespace stk;\n\nSineWave input;\nArdStreamOut output(Serial);\n\nvoid setup() {\n  Serial.begin(115200);\n\n  Stk::setSampleRate( 44100.0 );\n  input.setFrequency( 440.0 );\n}\n\nvoid loop() {\n  output.tick( input.tick() );\n}\n\n<\/code><\/pre>\n
We just copy the input to the output which is Serial in this case. And the output in the Arduino Plotter looks as follows:<\/p>\n
\"\"<\/p>\n
The ArdStreamOut is expecting a stream. This is quite powerful if you consider that Arduino provides different implementations of Streams!<\/p>\n
The following Arduino specific classes are provided:<\/p>\n