Import the artwork that you want to add your SFX to! For this tutorial I'll be using one of my Super Ladies: Epitome.
Type out the sound effect word that you'd like to add and choose a font that fits the word. This is pretty important. After all, you don't want a heavy “THUD” to be in a light, script font!
Right-click on your text layer and choose Rasterize Layer from the menu (Layer – Rasterize from the top of the program window). We're going to add a color gradient to this text, so let's click on the Lock Transparent Pixel icon in the layer palette (Layer – Layer Settings – Lock Transparent Pixel).
If you wish take a gradient tool and add a gradient to the text. I've used a yellow to red gradient.
Add a stroke to the outside of the sound effect by clicking on the Border Effect icon in the Layer Property palette. I'm using black for the outline color with a large Thickness of Edges number.
Now we're ready to make this SFX pop! Use Ctrl+T (Edit – Transform – Scale Up/Scale Down/Rotate) to make the letters larger and make them follow the general direction of the motion.
Next, we're going to make this look really cool! Select Edit – Transform – Mesh Transformation and a grid will appear over your text. Each of the boxes at the intersection of this grid are control points that we can use to manipulate the sound effect. If you want more control, look in the Tool Property palette BEFORE you start moving points. Adjust the Number of Horizontal Lattices and Number of Vertical Lattices to a higher or lower number, depending on how much detailed control you want on your transformation.
Move the control points to further refine the shape of the sound effect. For this image, I'm making it look like the beginning of the text is further away than the end of the text, so it looks like the sound is getting louder as it approaches the viewer.
With a little patience and tweaking, you can also make curved text this way too! Press Enter on your keyboard when you're done editing the shape of the text.
You're done! Display your awesome sound effect for everyone to see!