The key message is for programme makers to consider the intelligibility of their content at all times.
Make sound a priority. Think of it at all stages of the production, from planning to post-production.
Unclear speech, unfamiliar or strong accents, background noise and background music can all affect intelligibility. Audibility can be particularly compromised when more than one of these issues combine.
Reducing background music by one PPM point (peak monitor reading) allows many more people to hear what is being said without necessarily compromising editorial vision.
BBC's Audience Services monitors the number of complaints we receive about a programme's audibility. If a substantial number of justifiable complaints are made, production teams will be contacted and asked to remix the programme for future transmission, and to confirm that any subsequent episodes in the series are mixed to achieve the best audibility possible.
Deaf children may use a combination of techniques to interpret output.