The height of the wave from its highest point or peak to its zero level in any given sample or at any point along the line of the wave; the power of a sound wave expressed by the height of the sound wave in a given instance.

Think of a downtown street with a series of five buildings. The first building is one story, the second is two stories, the third is four stories, the fourth is two stories and the fifth and final building is one story tall. These buildings represent a sound wave. The street is the zero level or reference level from which the buildings are measured. Below the street level the buildings have basements. Above the street level the buildings rise a certain number of floors. The tallest building, the center building, is four stories tall. If all the five buildings in the row represent one cycle of a wave, then the amplitude would be the height of the tallest building – five stories.

Amplitude can be measured at any point along a wave at an infinite number of points (a continuous analog wave contains an infinite number of individual points). The amplitude of the first building in the previous example is one. The amplitude of the second building is two, etc. The amplitude of the entire wave cycle is four – the highest point at building three.

As we increase the volume of a given musical signal (or any sound), we increase the amplitude of the sound wave. The frequency does not change with amplitude. A 2,000 Hz tone may have a very small amplitude or a very large amplitude, but it will still retain the 2,000 Hz frequency.

Frequency determines the number of cycles produced in a specified amount of time (usually one second. The frequency affects the wavelength of a given signal since in one second a signal can only travel so far. The wavelength is the distance from identical points on a two wave cycles in a series such as the horizontal distance from the peak of cycle one to the peak of cycle two. As the wavelength increases (grows longer), the frequency decreases. For instance, a 20 Hz tone (very low frequency) has a wavelength of around 56 feet, while a 20,000 Hz tone has a wavelength of around two-thirds of an inch! When a large number of cycles are squeezed into a small distance (the distance sound can travel in a single second), we get a high frequency with subsequent small wavelengths.

The amplitude does not affect a given signals frequency and thus does not affect its wavelength. Wavelength measures a signal horizontally from left to right. Amplitude measures the signal vertically up and down from a zero point. Frequency affects the tone of a sound such as being high-pitched or very low, and amplitude affects whether that tone is loud or soft.

Amplifiers increase the amplitude of a signal. As an analog audio signal comes into an amplifier, it is a low level or line level signal. The amplifier then props up this signal by an equal amount at all points across the signal. Think of taking the buildings example from earlier and adding twenty stories to each of the buildings. The frequency will still be the same and the signal will be unchanged except that the signal, the buildings, will be taller or have a greater amplitude. And with greater amplitude comes more power and thus higher sound pressure levels (it sounds louder).

Thus, frequency affects the number of cycles a signal packs into each second. The frequency in turn determines the wavelength of the cycles since waves must get smaller as more cycles are squeezed into a given space (and larger as less cycles are put into the space). Amplitude does not affect the wavelength of the frequency of the signal, but instead affects how tall the peaks (and all other points) are and how low the troughs (and all other points below the zero line) are. This change in height caused by amplitude alters the power of a signal with greater amplitude equaling more power (for instance, Mt. Everest would be much more powerful than a rolling hill).