Surround sound and control rooms 539 2 3 4 5 sound, which may be warning of danger in real life, but it is not much use in a cinema, except in IMAX, perhaps. The mixes will be played back in theatres that comply with a reasonably tight range of electro-acoustic and acoustic requirements. Due to the sheer cost of film production, mixing will usually be carried out by skilled, experienced, and knowledgeable personnel, who will almost invariably limit their creative exuberance to getting the very best out of what they have to work with. They will not get too carried away creating wonderful effects in the mixing room which will be detrimental to the experience in the theatres. The success of a film tends to ride on how many people see the first screenings in the cinemas and recommend the experience to their friends. Creating nonsense does not help this situation. The objective is usually to create a one-off, big performance, and it generally means that high quality programme material and equipment are available to achieve the high standards that are normally expected. However, mixing room size can demand different solutions to the problems of achieving these high standards if the mixes are to transfer to the cinemas with the required degree of accuracy. In all cases, though, it is desirable to keep the quality of the mixing room a good jump ahead of the likely playback room performance. This needs to be especially so in terms of the perception of detail whilst maintaining the overall frequency responses within the accepted ranges. The whole concept of the various Dolby surround formats is to deliver a balanced programme to a group of people, with no particular `sweet spots'.