Science has taught us that sound is air molecules compressing and expanding in waves. The highest point of the waves is interpreted as amplitude and is measured in decibels. When reading these measurements negative infinity is silence and zero is the loudest. How many times a second the crest of the wave passes a giving point is known as frequency. Frequency is measured in hertz and musicians refer to it as pitch.
Sound can travel, or propagate through three different mediums. They are liquids, solids and gases. We perceive sound for the most part through the gas medium as it travels through the air 1,126 feet per second. Depending on the medium, sound waves move faster or slower. For instance sound travels faster through a solid then through the air because the molecules are closer together. When sound arrives at different mediums one of the following things will happen: absorption, diffusion or reflection.
When sound is absorbed it will stop traveling. This can be useful because it can control unwanted reverberations. If a room is “dead” then the surfaces will absorb a large percentage of the sound. Diffusion is when the sound is broken up and reflected into many different directions. This allows the sound to be absorbed easier and at the same time prevents standing waves which we will discuss later in this section. When the sound bounces off the surface of the medium it is called a reflection. This is heard in reverberations and for the most part, is beneficial, but can lead to problems such as standing waves.
Standing waves are most commonly found in rooms with parallel walls allowing sound waves to cancel each other out. When one sound wave is reflected in the exact opposite of itself, or 180 degrees out of phase, it will cancel itself out. When this occurs, the sound wave loses energy and therefore becomes quiet. Another major problem that can occur is low frequency build up. Low frequencies are harder to absorb and therefore can become out of control easier. As the low frequencies build up phase issues become apparent. This can cause the listener to perceive the bass as missing. In addition, the human ear has a hard time perceiving low frequencies. These issues can lead the listener to over compensate with their recording techniques.
Wherever you are recording whether at home or in the studio try to keep the concepts we discussed in mind. If you are having issues some useful tips might be to try and angle your sound source so that it is not pointed directly at any walls. This will help to avoid phase issues. In addition, try not to record in any room that is completely square. Curtains, blankets and other sound dampeners can help to absorb sound but remember that they will only stop mid to high frequencies and cannot help with any low frequency build up issues. Be sure to experiment with rooms as you never know what amazing sounds you might find in some hidden room at your location.