psd amplitude scaling

If one creates a 1V RMS sine wave, e.g. with a peak value of 1.414 or

peak-peak of 2.83, then computes psd, the resulting amplitude is around

24 dB, yet classic theory dictates the answer ought to be 20 log(1) = 0
dB.

This offset seems consistent across various frequencies/sample
rates/amplitudes.

Can someone illuminate the amplitude scaling of the psd algorithm?

Thanks.

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