One of the difficult things about setting a ripple to music is that ripples overlap. The ripple at beat 1 will be influenced at Beat 2 if it is still on the screen when beat 2 starts. You control the overlap with the time span and the time between beats with the tMin, tMax values. These are the minimum and maximum triger values. If you want the threshold to start at 25 then set that as the value for tMin.

It also makes things easier if you add a couple of expression sliders to your comp to control the minimum and maximum values of value1 and value2. Just position your CTI between beats and adjust the the values to get a nice clean ripple. In this sample comp I set markers on the peak of the beats as a visual aid. Here's the expression:

value1 = effect("Slider Control")("Slider");
value2 = effect("Slider Control 2")("Slider");
t = thisComp.layer("Audio Amplitude").effect("Both Channels")("Slider");
linear(t, 35, 75, value1, value2)

I'm assuming the keyframes you've turned to Hold keyframes are the AudioAmplitude slider keyframes. Changing to hold doesn't do anything because there's a keyframe at every frame anyway.

It seems like you've got  a handle on the expression. tMin and tMax are the values you're sampling. value1 and value2 are the new range of values. Setting tMin to 25 means everything below 25 in the samples (Audio Amplitude keyframes) gives you your set value for value1 and anything above a tMax setting of 75 would give you the set value for value2. Anything between 25 and 75 would be linear. For example if value1 was 0 and value2 was 500 then a t(sampled value from audio keyframes) value of 50 would return a value of 250.

So now here's how the plug-in works.  CCRiple Pulse is waiting for the first in any pair of keyframes in the Pulse Level property to start a pulse. The value of the first keyframe can be anything. Now here comes the tricky part. The time of the first keyframe starts the pulse, but the second Pulse Level keyframe sets the rgb value of the displacement map and starts the time of the second pulse if there is a 3rd keyframe. The value at the center of the pulse also depends on the Amplitude. If the first keyframe was -100 and the second was 100 and the Amplitude was set at 100 then the value of the center of the pulse at the time of the second keyframe would be about half way between 0 and 256 or gray. If the amplitude was set to 200 then the value of the center at the second keyframe would be about 256 or white.

The size of the center of the pulse is controled by the Time Span. To see how this works set up a timeline with 4 keyframes equally spaced alternating between -100 and 100. Move the CTI the same distance past the lask keyframe. Now adjust the amplitude and timing until you get a black background white ring, black ring, and white spot. There are the values for your four keyframes displayed as concentric rings.

To make this effect work effectively with Audio Amplitude and an expression the key is to set the tMin and tMax values to correspond to the beats and adjust the value1 and value2 so one is positive and one is negative and the difference between them is about 200 for maximum displacement. Then adjust the Time Span and the Amplitude to control the size of the pulse rings. A little messing and you'll get it. The tMin and tMax and the timing are the key.

The Cycore manual explains the use of the controls but that's about all. When I use a plug-in for the first time I really try and figure out what the controls do. Some are easy. This pulse ripple effect is a little more difficult.

If you are ever confused about what the controls are doing start by typing the name of the plug-in in the Search Help field at the top right corner of AE. If you're still confused start by having everything set to zero and make some adjustments. The kind of footage you use depends on the effect you're trying out. For most distortion effects I'll use a nested comp made up of a solid and a grid.

Here's the best advice I can give you about what to do next. If you get something you like create a custom animation preset, save it with a name you'll remember, then make some notes. I have a spreadsheet with about 8 years of notes that I have made and hundreds of presets in my library. It's much easier than trying to remember everything.