In low frequencies, spline cusps/looping causes visual artifacts

[tadmn]

1. Create new instance
2. Set FFT Size to 512 (or something low)

You can see the spline smoothing is causing the line to "wrap back" on itself. If you set the smoothing to "0" it goes away

To fix we can either:

• Add more control points to the lower end of the spectrum. Maybe we can just linear interpolate more points to try to spread them out as evenly as possible, which is what the "uniform" variant of Catmull-rom really needs as input. This could also be an opportunity to create more interpolated points in the lower end of the spectrum so that they are more evenly spread out logarithmically
• Use the centripetal variant of the Catmull-rom. I did start testing this here https://github.com/tadmn/tad-bits/tree/catmull-rom-centripetal but it looks quite a bit more computationally expensive
• Try out this spline technique: https://signalsmith-audio.co.uk/writing/2021/monotonic-smooth-interpolation/