S2-C_OfflineAudioProcessor

Offline Audio Processor

This project is the C-language version of step 2 of the main project Real-time audio processing. Please refer to the README of main project for more information.

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Author

Thomas Hézard - Audio scientist and developer
www.thomashezard.com
thomas.hezard [at] thz.fr

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License

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

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🎯 Objectives

Your goal is to translate the final algorithm of the previous step into platform-agnostic, real-time-compatible C code. In order to simplify this task, you will do this in the most simple context: a CLI program called OfflineAudioProcessor.

The project structure is already established, and the provided program does the following:

• open a WAV audio file and read it (using the external library AudioFile),
• apply some audio processing to the data,
• write the modified data in a WAV audio file (using the external library AudioFile).

This program is not real-time, but the provided architecture is compatible with real-time constraints.

NB: The main program is written in C++ for easier audio file handling, but you will only have to write C code, you do not need to know the C++ language.

The proposed architecture contains a struct named AudioProcessor with its associated functions, defined and implemented in the files audio_processor.h and audio_processor.c. This struct is used in the main function - main.cpp - as follows:

• construction of an instance of AudioProcessor at the beginning of the program: main.cpp line 35,
• preparation of the AudioProcessor: main.cpp line 36,
• processing inside an audio process loop: main.cpp line 52,
• destruction of the instance at the end of the program: main.cpp line 67.

All header and source files are located in the sources directory.

As in step 1, the provided version of OfflineAudioProcessor does nothing more than copying input data into output data. Your objective for this step is to modify the AudioProcessor struct and its functions in files audio_processor.h and audio_processor.c, so that it performs the audio processing algorithm you implemented in the previous step. What you need to do is:

• adapt the definition of the AudioProcessor struct with all the needed variables (memory buffer, parameters, etc.),
• if your AudioProcessor needs some prior information before starting the rendering loop, like sample rate or parameter values, these information should be passed in the prepare_audio_processor function, it is recommended to keep the new_audio_processor function as simlple as possible,
• adapt the prepare_audio_processor and destroy_audio_processor functions and, if needed, the call to prepare_audio_processor in the main function,
• adapt its ap_process function's implementation (you shouldn't have to modify its declaration).

Once your modifications are completed and functional, you can design and implement tests to check that the results are exactly the same as in the previous step.

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⚙️ How to compile and run

Compile and run on Github Codespace

This project can be compiled and run in a pre-configured environment on Github Codespace:

1. Fork this repository to your own Github account,
2. On your fork's page, click the green Code button → Codespaces tab → Create codespace.

Once in the Codespace, open a terminal and follow the instructions below to compile and run the project.

Compile and run from the command line (Github Codespace or local)

Compile out-of-source with CMake and make

Type the following commands from directory S2-C_OfflineAudioProcessor:

mkdir build
cd build
cmake ..
make

Compile out-of-source with g++ or clang++ (or any other C/C++ compiler)

Type the following commands from directory S2-C_OfflineAudioProcessor (replace g++ with your compiler if needed)

mkdir build
cd build
g++ -std=c++11 ../sources/main.cpp ../sources/audio_processor.cpp -o OfflineAudioProcessor

Compile and run from a Cmake or C++ IDE

You can also open this directory from your favourite Cmake or C++ IDE and work form there.

Running the compiled program

Once built, run the executable with the following command:

./OfflineAudioProcessor INPUT OUTPUT

INPUT must be the path to a WAV mono audio file. You can use the provided file Marimba.wav.
OUTPUT must be the path to a non-existing WAV audio file.
For example, after building with cmake, while still inside the build folder, you can run:

./OfflineAudioProcessor ../Marimba.wav ../output.wav

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Credits

Thanks to Adam Stark for AudioFile C++ library, copyright (c) 2017 Adam Stark.