Click here to purchase the entire book in PDF format. Scaling methods Let's design a test to see how loud two different sounds are perceived to be. We could do this in two general ways, using either direct scaling or indirect scaling. If we use direct scaling, then we play the first sound for the test subject and ask them to rate how loud it is on a scale (say, from 0 to 10). Then we play the next sound and ask them to rate that one. In this case, we are directly asking the subject to tell us how loud each sound is. We can then compare the two answers to see whether one sound is louder than the other. Or, we could see if two people rate the same sound with the same perceived loudness. A different way to do this test would be to play one sound, then the other and ask ``which is the louder of the two sounds?'' In this way, we find out whether one sound is louder than the other indirectly. We are not asking ``how loud is it'' - we are asking ''which one is louder'' and figuring out later how loud they are by using the results. This is called indirect scaling because we're not directly asking the subject for the answer for which we're looking.