Write the files onto a CD (or similar digital media) for playing back to the subjects. Most computers now come with a CD-RW or DVD-RW and the necessary software. These should be the files with headphone correctionss and the instructions such as "kettle A". It is important that the order of the files on the CD is randomised, you shouldn't order them from cheapest to most expensive, for example. The order should also be changed for each subject, so there will be a different CD for each subject. If the order isn't changed between subjects, this can bias results. It is also possible to write a short computer program to audition the files in random order, but it is only worth going to this effort if you intend to prepare and run many tests.