Interpolation for data sets from different instruments?

I have spectral data which is poorly aligned. It was taken from two different devices, such that some spectral data is between, say, 1 kHz and 3 kHz with 0.1 kHz steps, and other data is between 1.1 kHz and 3.3 kHz with 0.2 kHz steps.

What's the best way to interpolate these data such that I get an 'aligned' dataset, e.g. all data is between 1 kHz and 3.3 kHz with 0.1 kHz steps?