A flute, a violin and a trombone all play the note "A". The conductor plays a tone generator that produces a perfect 440 HZ pitch. All the three instruments correctly match the pitch, but it is very very easy to tell which sound is the flute, which one is the violin, which one is the trombone, and which one is the tone generator. If they are all producing a 440 hz tone, how can you tell them apart?