Sometimes nerves manifest themselves by making your voice sound strange. This is actually the tension in your neck muscles pushing against your voice box. Try to loosen those muscles, maybe if you live close enough to the interview location a really hot shower on your neck, or cup of tea or coffee 15 minutes before can help to soothe your voice box. Remember the importance of a confident handshake. You get to check the employer out and of course they get to assess you.
Employers use a variety of formats and techniques.
You can phone the employer to find out the style of recruitment used by the organisation and prepare yourself accordingly. In general, panels are utilised by government and community related organisations. Prior to the interview find out the names and position of the panel members. Panels may utilise an expert from the discipline area as well as someone from human resources, and often there will be someone who has experience in the line of work from another section. Direct your initial answer to the person who asked the question, but make sure the other panel members in the important details of your answer.