As discussed in the Study Guide, loudness depends on three factors: the characteristics of the stimulus; the characteristics of the context; and the state--or sensitivity--of the auditory system. If you downloaded the Frequency Generator you can examine some of these issues.

As far as the characteristics of the sound context, there are two main characteristics--intensity and frequency. The effects of intensity are apparent: a high intensity sound will appear to be louder than a low intensity sound. The effects of frequency are a little more subtle. To explore the effects of frequency, use the frequency generator to play a 3Hz tone. Now play a 30,000Hz tone. You shouldn't have heard either tone as they are both outside of the adult human's range of hearing. No matter how loud you turn up the volume you just won't hear them. Now try some tones within our audible range (20-20,000Hz.) Note, as pointed out in the Study Guide, that midrange frequencies will seem louder than low and high frequencies. Try playing a midrange frequency (like 4000Hz,) and then play both low (500Hz) and high (10,000Hz) frequencies. Did you notice how much louder the 4000Hz tone was? Make sure that you look over the equiloudness contours in the Study Guide to see this represented graphically.

The characteristics of the context can also effect loudness. The physical layout of the environment in which the sound is heard can effect loudness. For instance, spoken words will seem louder in an empty stairwell than they will in a carpeted room or outside in the open air. Other sounds present at the same time as the auditory signal can also effect its perceived loudness. An example of this is noise in the environment. For example, if you have ever tried to carry on a conversation with someone from a pay telephone on a busy street corner, you have suffered the effects of environmental noise! In this environment you probably had to increase the loudness (intensity) of your voice in order to be heard; your conversation partner probably had to do the same. This environmental noise functions as a mask-- a sound present at the same time as the auditory signal that makes it harder to hear. As it turns out, the most effective masks are those tones which are just lower in frequency to the auditory signal. The reason for this can be seen in the following figure:

As you can see from the figure, the mask--with its wide area of disturbance--will make it harder for the higher frequency signal to be uniquely encoded.

Obviously the state, or sensitivity, of the auditory system will effect loudness. If any defects exist in the ear the reception, transmission or transduction of an audio signal could suffer.

The Experience of Pitch

The experience of pitch depends on two factors: the state of the auditory system; and the characteristics of the stimulus. Under the heading of the state of the auditory system are the place and periodicity theories of pitch perception. The place theory of pitch perception is the theory that each frequency has its own particular area of response on the basilar membrane:

The periodicity theory of pitch perception is the theory that the entire basilar membrane vibrates in response to an incoming signal; that the basilar vibrates in period with the incoming sound wave.