Some Basic Concepts

For our EE 421 group project we will be designing a guitar tuner that can determine different strings based on a sound input. There are many parts to this and as we go we will try our best to explain everything in a concise manner. The following post talks about the basic ideas of sound waves along with some other information that may be helpful to know.

A sound wave is caused by a vibration given off by an object moving through some static medium. This medium could be air, water, or anything that allows this wave to pass through it. The vibrations given off by the object, which in our case is going to be the plucking of different guitar strings, creates disturbances in the particles of the medium causing them to move back and forth. These disturbances through the air also create varying fields of high and low pressure that move the particles, which are known as pressure waves. In a sense a sound wave is also a pressure wave. The motion at which the air particles are moving back and forth is called the frequency of the signal.

Frequency2

The standard definition of frequency is the number of occurrences of a repeating event per unit time. In our case the sound wave frequency will be how often the particles of air vibrate when a sound wave from the vibration of the guitar strings passes through the air. A common measurement for frequency is Hertz (Hz). We define a Hertz to be:

1 Hertz = 1 vibration / second

As the sound wave moves through the air each particle has a domino effect on the other particles, meaning that once the first particle begins to vibrate at a certain Hertz it causes the particle right next to it to vibrate at that same Hertz. This continues until there is an obstruction that blocks this from occurring. This chain of particle vibrations is what allows us to hear the sound once the guitar string is plucked. Our eardrum can detect the changes in air pressure caused by the sound/pressure waves emitted from the guitar strings. Humans are capable of detecting sound waves with a wide variety of frequencies, generally from around 20 Hz to 20,000 Hz. Anything above or below that we cannot hear!

The pitch of a sound is directly related to the frequency at which the sound wave is traveling. A high-pitched sound will come from a high frequency sound wave and vice versa, a low pitch sound corresponds to a low frequency sound wave.

pitch

Using a guitar for an example, when the bigger, heavier strings are plucked it will vibrate slowly creating a low pitch. When a thinner, lighter string is plucked it will vibrate quickly and give off a higher pitch. Another example of this is when we talk! The sounds that come out of our mouth when we speak are caused by our vocal cords vibrating in our throat. Depending on how much air we force past our vocal cords determines the loudness and pitch of our voice.

The last thing I want to talk about in this post is the tone of a sound, specifically a musical tone since we are going to be using different guitar strings to demonstrate our project. A musical tone consists of many parts, the duration, pitch, intensity, and timbre. We spoke about pitch above, the duration of the tone is how long it lasts, the intensity is how loud the tone is, and timbre is the quality of the sound. Depending on the type of tone you are looking for some of these categories can vary. For example, a simple tone will only have one frequency but can vary in intensity. A complex tone is made up of two or more simple tones and can vary in more than one category.

Differences between pitch, frequency and tone

Pitch is each person’s subjective perception of a sound wave.  Pitch can be classified as high or low depending on the frequency. A high pitch sound wave corresponds to a high frequency sound wave while a low pitch sound wave corresponds to low frequency sound wave. On a guitar with a big heavy string will vibrate slowly and produce a low pitch while on a guitar with a lighter string will vibrate faster and create a high pitch. Sound waves themselves do not have pitch, their oscillations can be measured to obtain a frequency.

Frequency of a wave refers to how often the particles of a medium vibrate when a wave passes through the medium. Frequency is measured in Hertz. Pitch can be determined only in sounds that have a frequency that is clear and stable enough to distinguish from noise. Pitch is closely related to frequency, but the two are not equivalent. Frequency is an objective, scientific attribute that can be measured while pitch is a subjective attribute

Tone refers to the quality of sound. A singer or flautist can produce a perfectly pitched G sharp, but if the tone quality is poor, what results may sound dull or weak. Tone is commonly used by musicians as a synonym for pitch.

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