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Sound Effects 101: Introduction to Sound Waves

On an elemental level, it is easy to explain how we perceive sound. That is, for sound to be detected, there must first be a disturbance in the atmospheric pressure. This disturbance – that can be caused by the ringing of a phone, the movement of a person’s vocal cords, or a hammer striking a nail – forms sound waves. These sound waves travel through the air from the source of the disturbance where they eventually reach and vibrate the eardrum. Hair cells, or cilia, within the inner ear convert these vibrations (sound waves) into electrical signals that are interpreted by the brain as sound.

This is a simplistic explanation of how sound is detected. However, not all sounds are created equal. In fact, our sense of sound is so refined that we can automatically recognize a familiar voice without seeing their face or distinguish the cry of a newborn from that of an older child. We are able to distinguish different sounds by their frequency (pitch) and volume. To understand these two sound elements, it is important to have basic knowledge of the anatomy of sound waves.

Anatomy of a Sound Wave

Technically, one sound wave is comprised of a compression and a rarefaction. If you were to take a hammer and strike a nail, this action would cause a disturbance to the surrounding air pressure, causing the molecules to move up and down in a wave like motion. When the air molecules move up from the normal air pressure point, they become tightly compacted together. This movement is known as a compression. Conversely, when the air molecules sink down and below the normal air pressure point, this movement is known as a rarefaction.

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Frequency

One complete wave cycle is composed of one compression and one rarefaction. Frequency is defined as the number of wave cycles that occur per second and it is measured in Hertz (HZ). As a rule of thumb, the human ear registers frequencies between 20Hz to 20KHz. One KHz consists of 1,000 wave cycles per second. So, 20KHz would equal 20,000Hz.

Frequency is often referred to as pitch. High pitch sounds correspond to high frequency sound waves (the sound of screeching tires) and low pitch sounds correspond to low frequency sound waves (the sound of a bass trombone).

High frequency sound waves are thinner (due to having more wave cycles per second) and weaker then low frequency sound waves, but they travel faster and farther then their low frequency counterparts.

Amplitude

Amplitude is directly related to a sound’s power and intensity. We interpret a sound’s amplitude as volume. Dropping a ten-pound boulder from the roof of a 5-story building to the pavement below would disturb the surrounding air pressure more then a 12 oz. shoe being dropped from the same distance. The boulder would create a much higher sound wave. Therefore, the volume of the boulder crashing to the pavement would be interpreted as considerably louder then that of the shoe.

Knowing the basics of your desired craft is essential if you are to perform it well. If you are a budding sound designer or are considering becoming one, having a basic understanding of sound waves is a must. With the need for quality sound effects expanding beyond radio, television, and film to include other media such as video games, multimedia, cell phones, and even You Tube, the possibilities for sound designers are virtually endless.

If sound design is not your passion, but you are in need of hard, background, Foley, or electronic sound effects, high definition sound effects libraries containing numerous sound effects can be purchased on-line. With the advent of the Internet and e-commerce, locating and purchasing top quality sound effects is as easy as 1, 2, 3.

Source: ArticlesBase.com

An Introduction to the Properties of Sound for Recording Musicians

An Introduction to the Properties of Sound for Recording Musicians

by Clay Butler

Obviously, if you’re reading this article, you have an interest in recording.   I’m sure you also have some notion as to what sound is.  Sound is what we hear, right?  Well, yes.  But there’s a lot more to sound.  Knowing what sound is and how sound works is the key to getting a quality recording.  Let’s get our feet wet in sound waves (pun intended).

Simply put, sound is Acoustical Energy, or vibration.  More specifically, sound is vibration propagated through a medium, which is then received by our ears and interpreted by our brain as sound.  The reason I say the vibrations are interpreted by our brain as sound is because acoustical energy still exists that we cannot perceive as sound (more on this later).  For example, while a dog might go nuts from hearing a dog whistle, we as humans cannot interpret those vibrations as sound.  Radio, cell phones, Wi-Fi, microwave ovens, and RADAR all use sound waves that we as humans just can’t hear.  So, in essence, when we refer to sound, we really refer to our perception of vibrations.

Sound vibrations that are propagated through the air (or any other medium for that matter) are in the form of transverse waves.  Thus, you could also say that sound is really rapid fluctuations in air pressure.  The vibrations from a vibrating body, such as a guitar string, push and pull on the surrounding air, creating positive and negative pressures.  These waves occur as the molecules of air are slammed closely together as they are pushed by the vibrating body.  The part of the wave consisting of positive pressure, where the air molecules are slammed together, is called a compression.  Negatively pressured parts of the wave, where the air molecules are pulled apart from each other, are called rarefactions.

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How loudly a sound is perceived is determined by how hard the air gets pushed by the vibrating body.  The harder the air gets pushed, the louder the sound.  Although this is typically referred to as volume, in reference to acoustical energy, it is called Sound Pressure Level (SPL).  The scale used to measure Sound Pressure Level is the Decibel scale, or dB SPL (more on the other Decibel scales in a later article).

The pitch of a sound is a function of frequency.   How frequently a vibrating body pushes the air determines how high or low the tone of the sound is perceived.  The more frequently the air gets pushed, the higher the tone of the sound.  As the air gets pushed less frequently, the tone sounds lower.  Therefore frequency is expressed as the number of sound waves occurring over time.  The scale used is known as Hertz (Hz), which signifies the number sound waves per second.  For example, the note “A” below “Middle C” on a piano is 440Hz.

The frequency spectrum is broken up into three parts.  The Audible Range for humans is roughly 20Hz to 20,000Hz (or 20 Kilohertz, abbreviated as KHz).  The frequencies below 20Hz are categorized as Infrasonic.  All frequencies above 20KHz are referred to as Ultrasonic.

Let’s look again at sound being all about our perception.  Generally, we don’t hear the sound emanating directly from its source.  The majority of the time, we hear sound after it bounces off the surrounding walls, along with any other nearby surfaces, and interacts with the room.  We call this acoustics.  Understanding how acoustics influence sound, especially those sounds you’re trying to record, better enables you to get the sound you want without any surprises.  Each time a sound wave is reflected back into an acoustic space, our perception of that wave changes, especially when you hear sound coming directly from a sound source in addition the reflected waves.  This is why it’s not uncommon for a pro recording studio to spend hundreds of thousands of dollars on architectural design and acoustic treatment, so that those extra reflections and wave interference are eliminated.

http://www.claybutlermusic.com

© 2009 Butler Productions

Source: ArticlesBase.com