Most musicians and singers are also trained to have good relative pitch. This is the ability to identify a note by comparing to other notes. This means that if you play a note then ask the person to sing the note, say, an octave above that note, they will be able to. Similarly, if you play two different notes, and tell them what one of them is, they will be able to tell you what the other was by comparing to the first.

Some singers and musicians have absolute pitch. If you have absolute pitch you are able to name any note you hear, or sing any note named, without comparing to any other note. Absolute pitch is very rare, even among musicians, and cannot be learned.

At the opposite end of the spectrum, some people are tone-deaf. This means that they cannot hear the difference between notes: they still hear all the sounds, they just don't sound different to each other. People may be born tone-deaf, or may become tone-deaf as a result of stroke or brain injury.

In European languages (such as English, French and German) we vary the pitch of our speech to make it sound more interesting. Some changes in pitch can affect the meaning of a sentence, for example we often increase our pitch at the end of a question. But people can be understood in English, even if they speak in a complete monotone.

In other languages, such as Chinese and Yoruba (an African language), changing the pitch of the word can completely change its meaning. These are called tonal languages. Interestingly, there are a lot fewer tone-deaf people and a lot more people with absolute pitch in populations that speak tonal languages, than in European populations. Researchers aren't sure if tonal languages came about because the people were better at distinguishing notes, or if people became better at distinguishing notes because speaking a tonal language acted as training.