The max. frequency value in the spectrum analysis window is in some cases too optimistic. It seems to be oriented on max. frequency level (red), not on average frequency level (blue). When the average level drops down, while the max. level stays high, this an indication that the noise level drastically increased at higher frequencies caused by alias effects by violating the nyquist limit or by high frequency mismatch during compression/decompression.
In this case the rating value is misleading (higher value - worse quality).
