How does the Audio Spectrum CHOP logarithmic scaling work?

When using the Audio Spectrum CHOP with Frequency <-> Logarithmic scaling set to 0, the sample index corresponds to a frequency. I.e. sample 1,000 represents 1,000 Hz. But when the scaling is set to 1, what is the relationship between sample index and frequency? It doesn’t seem to be as simple as the linear frequency response plotted on to a logarithmic x-axis.

What underlying math/algorithms are used to show the frequency response in logarithmic scaling? And is there a general formula I can use to convert sample indices into their corresponding frequency values?

Thank you very much in advance for any help!