Naive Instruments

A naive approach to audio signal processing.

It aims to be a command line application for editing & processing audio signals.

Installation

At the moment, the makefile is only set up to build for Mac OS.

You will need boost!

brew install boost

Compile it:

make

Add the bin/ directory to your path.

.bashrc

PATH=$PATH:~/path/to/this/repo/bin

To run the tests you will need ffmpeg:

brew install ffmpeg

How to add a new command

To create a new command you need do two things:

1. Create a new class (probably a subclass of AudioCommand) in src/commands/<your-command's-name>.h

2. register the command in src/main.cpp

Here's an example of a very simple command:

// src/commands/NoiseCommand.h

// The first thing we do here is to include the library, to make all the
// classes available:
#include "../lib.h"

// Next we declare a class which extends the `AudioCommand` base class. This
// has helpful methods for command line options, audio input/output from
// streams and sending audio to the speakers.
class NoiseCommand : public AudioCommand {
public:
  // We have to manually add the class constructor from the base class. This is
  // some boilerplate code that I hope to eliminate the need for soon.
  using AudioCommand::AudioCommand;

protected:
  // By overriding the `describeOptions` we declare how the user may configure
  // this command using optstrings.
  //
  // Helpful video about command line tools:
  // https://www.youtube.com/watch?v=kgII-YWo3Zw&t=1225s
  void describeOptions() override {

    // This helpful method sets up the standard options used by the `output`
    // method later on. Allows the user to use the `-o <output-file>.wav` to
    // send audio to a file, or pipe the WAV output to stdout.
    describeOutputOptions();
  }

protected:
  // We define the actual signal processing part of our command by overriding
  // the `action` method.
  void action() override {

    // Create a `Noise` signal (a subclass of `Signal` which outputs white noise
    Noise noise;

    // We send our signal straight to the output. The `output` method will work
    // out where to send the audio depending on the user's command line options.
    output(noise);
  }
};

For more examples see the files in src/commands

Control Signal shorthand

PLEASE NOTE: I'm kinda planning to change this a lot soon based on what I've learnt from using it for a while. Watch this space..

You may use a shorthand for control signals. These are made out of a sequence of time-steps.

Use _ to indicate that the signal should remain static for one step.

Use ~ to indicate that the signal should be gliding toward the next value for a step.

Use a number to set the value of a step.

Use a colon : for tempo indication.

(Maybe,) use ± for lfo vibrato?

Examples

Start at 440Hz for 4 steps, then switch (instantly) to 550Hz

440Hz____550Hz____

Start at 1 and glide to 0 over 4 seconds

1s: 1~~~~0

Frequency signal for Twinkle Twinkle Little Star

120bpm:
c_ c_ g_ g_ a_ a_ g__  
f_ f_ e_ e_ d_ d_ c__