Fundamentals of sound BLOG
Sound waves are vibrations that travel through a medium, usually the air. This vibration causes a pressure and displacement of particles. Air molecules oscillate back and forth into each other until the wave of energy makes it to your ear and you can perceive it as sound. In its most basic form, this can be viewed on a sine wave.
1. The x-axis represents time with the centre line representing the equilibrium position of each molecule - where the particle has zero energy.
2. The period is the time it takes for the molecule to complete one oscillation. The back and forth motion is called a cycle. The less time it takes for a molecule to oscillate back and forth, the higher the note we perceive. The period is measured in seconds which closely relates this to the idea of frequency. Frequency is determined by the amount of cycles per second. It is measured in Hertz (Hz). Humans can perceive frequencies from about 20Hz - 20000Hz.
3. The peak is called the compression.
4. The trough is called the rarefaction.
5. Amplitude is the height. The higher the amplitude, there is potential for volume increase.
The decibel (dB) is based on the logarithm of the ratio between two numbers. If the reference value is fixed then it can be used as an absolute unit. The Decibel is strictly ten times the logarithm to the base ten of the ratio between the powers of two signals. The log is how many times we have to multiply a certain number by itself to get the number we want.
When multiple sound waves are combined they create a single wave called a complex wave. Two waves of equal amplitude and frequency combined will produce a sound that is twice as loud.
Acoustic phase cancellation happens when mics are placed at different distances from the instrument. One mic will inevitably pick up the signal slightly later because it is further away.
“In a reverberant space, the sound perceived by a listener is a combination of direct and reverberant sound. The ratio of direct sound is dependent on the distance between the source and the listener, and upon the reverberation time. At a certain distance the two will be equal. This is called the ‘critical distance’” — Glenn White and Gary Louie (2005)
“Music is a mixture of sound pressure at different frequencies. Sound pressure, or sound pressure level, is the result of the pressure variations in the air achieved by the sound waves.”
Critical Distance. (2019, September 8). Retrieved October 15, 2019, from https://en.wikipedia.org/wiki/Critical_distance
Physics Archives. (2015, March 9). Retrieved October 14, 2019, from http://sound.education/tag/physics/
Production of sound. (2014, May 23). Retrieved October 13, 2019, from https://www.khanacademy.org/science/physics/mechanical-waves-and-sound/sound-topic/v/production-of-sound
The 3-1 Rule for Mic Placement. (2016, November 19). Retrieved October 14, 2019, from https://www.sageaudio.com/blog/recording/3-1-rule-mic-placement.php
What is sound? (2017, February 24). Retrieved October 14, 2019, from https://www.open.edu/openlearn/science-maths-technology/science/physics-and-astronomy/physics/what-sound