As we all know, frequency response, particularly at the extremes, is hardly the primary arbiter of sound quality in reproduced sound. If it was, all we would need is wide bandwidth components and equilizers. The "full spectrum 20-20k" is rather arbitrary at that. There is good evidence that we have a response to sound well above and below the specified frequencies. To complicate matters further, there are beats, or difference frequencies, that result from constructive and destructive interference within sound waves. A 22K and 23K tone, under the right circumstances, can produce a product at 1K, well within the audible range. By that thinking, the LP, with response out to at least 50K, would automatically qualify as a higher fidelity medium than redbook CD, which is already rolling off at 20K, and many of us think that it is. But even the staunchest defenders of the LP medium would admit that other factors such as surface noise partially mitigate the advantages of the format. Oh, and FM frequency response is generall given as 30-15K.