Low-resolution NPS artifact solution

In case anyone else is having a problem with low-resolution spikes in their Noise Power Spectrum, attached is a version of FindDQE that flattens the first 1% of the NPS by replacing it with the average of the second 1%. Should quash those crazy artefactual spikes, resulting in better NPS scaling.

Those spikes might also be indicative of a bad gain reference, so check that as well...