There was a law passed last year which states that it's illegal to speak using your IN voice when you're outside or your OUT voice when you're inside. They differ in volume and timbre. Failure to adhere to the law results in a fine. Some people are born without an IN voice though and that's why they speak really loudly in libraries and stuff. It's a genetic defect that can be rectified on the NHS but the operation has to come out of your own pocket as a symptom of the recent NHS reform proposals. You pay for it and then they send you an invoice.