After Effects - Audio Spectrum with Circles
Import your audio and use the Convert audio to keyframes option on the layer (right-click->Keyframe Assistent).
Then create an expression for the value that you want to modify based on the audio spectrum. In that case you probably want the radius or scale to be affected.
The simplest way to do this is to use the "expression pick whip". Just alt click the stop-watch icon to get the expression control menu.



Then click on the pick whip icon (marked above) and drag onto the left, right or center channel slider of your earlier generated "Audio Amplitude" layer. Now the values of the keyframes are 1:1 mapped to the chosen property of your circle object. Now you can do some math to the keyframes to amplify the animation or to reverse the direction.
F.e. you can do things like shown below, be aware that I chose to use the 2D size value as shown in the picture above, hence I have [temp, temp] at the end. If your property only has one value it will have only [temp] or with 3 values [temp,temp,temp]. You can also of course have separate values for each dimension.

Amplyify times 10:

temp = thisComp.layer("Audio Amplitude").effect("Left Channel")("Slider")*10;
[temp, temp]


Amplyify non uniform:

temp = thisComp.layer("Audio Amplitude").effect("Left Channel")("Slider");
[temp*5, temp*10]


Reverse direction:

temp = thisComp.layer("Audio Amplitude").effect("Left Channel")("Slider")*-1;
[temp, temp]


Easy In:

temp = easeIn(time, thisComp.layer("Audio Amplitude").effect("Left Channel")("Slider"), thisComp.layer("Audio Amplitude").effect("Left Channel")("Slider"));
[temp,temp]


The little "play" icon next to the whip offers you a lot of math expression functions to use here.