Spectrogram 2.0.0-alpha

Spectrogram is a .NET library for creating frequency spectrograms from pre-recorded signals, streaming data, or microphone audio from the sound card. Spectrogram uses FFT algorithms and window functions provided by the FftSharp project, and it targets .NET Standard so it can be used in .NET Framework and .NET Core projects.

Quickstart

(double[] audio, int sampleRate) = ReadWavMono("hal.wav");
var sg = new SpectrogramGenerator(sampleRate, fftSize: 4096, stepSize: 500, maxFreq: 3000);
sg.Add(audio);
sg.SaveImage("hal.png");

This example generates the image at the top of the page.

How to Read a WAV File

There are many excellent libraries that read audio files. Consult the documentation for those libraries to learn how to do this well. Here's an example method I use to read audio values from mono WAV files using the NAudio package:

(double[] audio, int sampleRate) ReadWavMono(string filePath, double multiplier = 16_000)
{
    using var afr = new NAudio.Wave.AudioFileReader(filePath);
    int sampleRate = afr.WaveFormat.SampleRate;
    int bytesPerSample = afr.WaveFormat.BitsPerSample / 8;
    int sampleCount = (int)(afr.Length / bytesPerSample);
    int channelCount = afr.WaveFormat.Channels;
    var audio = new List<double>(sampleCount);
    var buffer = new float[sampleRate * channelCount];
    int samplesRead = 0;
    while ((samplesRead = afr.Read(buffer, 0, buffer.Length)) > 0)
        audio.AddRange(buffer.Take(samplesRead).Select(x => x * multiplier));
    return (audio.ToArray(), sampleRate);
}