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12 tone equal temperament is the modern tuning system. In classical tuning the 4th and 5th interval produce 'perfect' harmonics because they are perfect ratios of the octave whereas b7, b9, etc are a bit out of tune. In the modern tuning all the intervals are just slightly imperfect even the 'perfect' ones. Look up the detail it's interesting
anyway, that's regardless of what frequency you start with
