Allolib is an open source library for interactive multimedia application development.

This repository contains two things:

• the spectrogram.hpp file which can be included in any Allolib project and gives access to the class al::Spectrogram
• the sound_design_with_spectrogram.cpp file which demonstrates utilizing a Spectrogram object

Spectrogram

The simplest way to use the Spectrogram object with an Allolib app is to put into any class that inherits al::App. In the class, it cannot be initialized outright and instead needs to be added as a member variable with an initializer list. The parameters needed in this list are the following:

• int buffer_size: determines how many past STFT outputs the Spetrogram should store and display
• int fft_window_size: determines how many bins the Short-Time Fourier Transform uses
• int hop_size: determines how many samples the STFT should wait for before calculating the next set of spectrum values
• float x,y: the x and y coordinate offset for the center of the spectrogram
• float w,h: the width and height of the spectrogram respectively
• float ler: legend ratio determines what percentage of the width should be used to display the spectrogram rather than the legend (values closer to 1 )
• bool is_log: boolean switch for linear or logarithmic frequency display The values used in in the sound design file are a good example of useful settings for this.

For it to work properly, some member functions need to be called throughout the App class. These instructions assume the object has name mySpec:

• onDraw(Graphics &g): call mySpec.draw(g) in this function to draw the Spectrogram object. When Allolib renders graphics, subsequent calls will overwrite previous ones.
• onSound(AudioIOData &io): there are two cases:
  • If there is a while(io()) loop in the onSound function, call mySpec.write_sample(io.out(0)) in it. The integer passed to the io object determines which audio channel the spectrogram will perform calculations on.
  • If there is no while(io()) loop, and nothing else in onSound internally uses a while loop, call mySpec.process_audio(io) as the last function within onSound.

If these steps are followed correctly, the object will process and render the spectrogram for any input.

Sound Design

The sound_design_with_spectrogram.cpp file contains my implementation of an Acid Bass synth sound. It also demonstrates how to use the spectrogram header file. An in depth explanation of how it works can be found in the repository linked here.

Further information

https://github.com/allolib-s24/notes-zeilerphone