These videos cover any topic that doesn't relate directly to a sound: linking, reduction, word stress, intonation. It also covers topics like idioms, real life English, and exercises.
Intonation: the pitch of the voice. These videos cover this imprtant topic, and how it relates to word stress and affects the character of your speech.
When a sound in a word changes or is dropped in the context of a sentence, that is reduction. For example, the word 'and' commonly reduces to 'nn'. Reduction is an important part of the character of American English: reduced syllables are flat in pitch (relating to intonation) and very quick (relating to rhythm).