After Effects: Audio react to beat then become fuzzy/blury?
Add a blur effect to the layer, and then use a similar expression to drive the amount of bluriness.

comp("Music").layer("Audio Amplitude").effect("Both Channels")("Slider")*1234


Replace the 1234 constant with whatever value makes sense for the effect–it may have to be a small number like 0.1234 if the effect is too much. One trick I often use is to use the original value as the constant, which means you can adjust the strength of the effect by using the controls for that effect, while still driving it with the expression:

comp("Music").layer("Audio Amplitude").effect("Both Channels")("Slider")*value