Frequency and Sound
https://www.musicgateway.com/blog/how-to/what-you-need-to-know-about-sound-frequency

Chrome Music Lab

https://musiclab.chromeexperiments.com/Experiments

Chrome Music Lab is a website that makes learning music more accessible through fun, hands-on experiments.

Online Spectrograph

https://spectrogram.sciencemusic.org/

Online Audio Signal Generators

https://onlinetonegenerator.com/

A Young Person's Guide to the Principles of Music Synthesis

by Beau Sievers

First published November, 2006

Table of Contents

1. Table of Contents

2. Introduction

3. Sound Waves and Oscillators

   1. Frequency and Pitch

   2. Basic Waveforms

      1. Sine

      2. Sawtooth

      3. Square

      4. Triangle

4. Building a Synthesizer

   1. Volume Control

   2. Filters

      1. Low Pass and High Pass Filters

      2. Band Pass and Band Reject Filters

      3. Properties of Filters

   3. Control Signals

      1. Envelope Generators

      2. Low Frequency Oscillators (LFOs)

5. Conclusion and Further Reading