SwiftUI - Animating Multiple Parameters withDifferent Curves

I'm exploring a sine wave rendering, and have built my view to have 3 controllable parameters:

• phase (to control the offset and allow animating "horizontally")

• amplitude (to control how high each peak is)

• frequency (how many complete waves there are)

I'd show you a screenshot but these forums not only don't allow embedded images, but you can't even link to one. (grrr)

My SineWave is implemented as a Shape, so it is already Animatable. I made amplitude and frequency an AnimatablePair and expose it as my shape's animatable data like this:

Code Block 
var animatableData: AnimatablePair<CGFloat, CGFloat> {
    get { .init(frequency, amplitude) }
    set {
        frequency = newValue.first
        amplitude = newValue.second
    }
}

This works, and I get a nice animation if I do this in my containing view:

Code Block 
        SineWaveShape(phase: phase, amplitude: amplitude, frequency: frequency)
            .stroke(style: StrokeStyle(lineWidth: 3, lineCap: .round, lineJoin: .round))
            .foregroundColor(.red)
            .onAppear {
                withAnimation(Animation.spring(response: 0.5, dampingFraction: 0.4, blendDuration: 0.1).repeatForever()) {
                    amplitude = 0.1
                    frequency = 4
                }
            }

Now I want to animate the phase as well. But I don't want this one to autoreverse, and I want it to be much faster. Unfortunately adding another withAnimation block next to this one has no effect, even if I have it as part of my animatable data. The last animation block always wins.

How should I approach this problem of wanting to animate two properties with two different Animation instances?