english

what does it mean to isolate something, such as "isolate higher harmonics"

Does it mean to remove higher harmonics? Or does it mean only the higher harmonics to be heard

In this context it means “to identify and separate out from something else" – for example other signals at different frequencies. You might do that visually with a measuring device like a spectrum analyser where you can "see" the difference between frequency components, or if the text is about sound / music and you have a good ear, you might be able hear these components amongst other parts of the overall sound scape. It does not explicitly mean "remove" or filter out the higher harmonics. Indeed you could do the opposite and throw away everything but the higher harmonics in this context.