Distortion Simulator

This interactive online app helps you visualize what happens when an audio signal pass through a non-linear curve, such as a Distortion Simulator. Simply drag a circular probe across graph with your mouse to scrub through signal amplitudes and hear different sounds. Using your computer keyboard will also allow faster control of the application.

It’s split into various useful sections. Start at the top by selecting your choice of distortion curve. There is three to choose from. Soft gives rounded peaks in the graph. Hard Limit chops the signal sharply at its peak. Asymmetric Diode Pair applies different settings for the positive half of the wave compared to negative side. Each of these options alters the nature of sound as well as the look of the graph.

How to Use the App

The primary work area is below the curve selector. This is where we have a big grid of the transfer function. A circular probe can be dragged around on graph to move over signal amplitude. You can also listen to what it sounds like when you moves the probe. You will hear a tone playing at that given input level. It shows how the curve work with different dynamic ranges. The reading is updated in real-time showing both input and output values.

The panel to the right show the harmonic assay. The harmonic assay looks at sound made from that curve. It shows you a spectrum of the harmonic content of what that curve make. And it will show you what the total harmonic distortion percentage is and which harmonic dominate. It then creates a bar chart showing how much energy each side (even/odd) have. So if your curve is symmetric you get mainly odd harmonics, whereas an asymmetric curve bring in even harmonics as well.

Below is where you’ll find effects controls and a signal generator. There are three test source options. Pure Sine Wave isolates only new harmonics produced by the distortion. Triangle Wave shows you what happens to existing partials. A two-tone signal exposes intermodulation products, which is how distortion affect two frequencies together.

Press the feed button and hold to sustain the chosen tone against the curve. You can fine-tune the effect using a few sliders. The drive control is an input gain that will push the signal harder into the curve for more distortion. Blend is a slider that mixes the processed and dry signals together. Post filter cuts off higher frequencies to adjust the tone. Output trim determines how loud the effect gets. Monitor level determine the master volume. Diode bias applies only in asymmetric diode mode to shift the curve’s unevenness.

Everything is accessible via keys on keyboard. To select distortion mode (hard, soft, diode), press 1, 2 or 3. To choose source (sine, triangle, two-tone), press S, T or D. To hold the currently playing tone like the feed button does, press and hold B. To start a comparison sequence of clean and distorted tones, press P. To stop whatever is playing, press Escape.

There are two additional features that offer more room for exploration. First, there’s the passport button. This stamps an A B distortion passport and plays a pre-programmed sequence comparing the clean signal to each distortion type. It lets you hear the difference without having to switch modes yourself. Second, there’s the blind transfer card, where a clean or distorted sample is generated at the same level so you can train your ear to detect changes in harmonics without being cued by levels.

For your curve of choice, adjust the drive slider until it sounds right to you. Too low and it will be transparent, too high and it will scream with clipping. The blend control could of been used to add a subtle amount of warmth without hurting the original clarity of your signal. Compare triangle and the sine waves as well. Each one respond differently to same curve depending on texture of your input. You will see how the triangle colors the more complex tones, whereas the sine is pure harmonic generation.

While turning dials, pay close attention to the harmonic assay. If you turn up the drive knob, you’ll see more peaks in spectrum as the THD value increases. When you alter the diode bias or switch from one mode to another, watch even and odd energy bars move. That visual feedback links the math behind the distortion’s curve with what you hear. You’ll better grasp why a given distortion sounds smooth or harsh.

This is a listening and exploratory tool. Listen to transition from clean to clipped. Take your time moving the probe along the curve. While it’s playing, use keyboard shortcuts to alter parameters quickly. Ideally this will help you develop a feel for how non-linear transfer curves affect audio signals. Begin with defaults and work up slowly increasing the drive to hear what happens.