The Sweet Sounds of Engineering
by Robin Hegg
Behind every musical recording you hear is the work of many engineers. Engineers research and develop new music technology and instruments, alter spaces to manipulate the behavior of sound waves, electronically alter audio signals when recording music or during live performances, and select and set up musical equipment to obtain the desired acoustic effects.
Sound is a vibration in the form of waves that move through a medium, like air or water. These waves enter the human ear and the brain perceives them as sound. Four basic behaviors of sound waves are absorption, reverberation, diffraction, and refraction.
Sound waves reflect off of surfaces just like light waves. Each time a sound wave reflects off a surface, some of its energy is lost. Absorption is the sound energy that goes through a material and is absorbed by it.
Reverberation is the sound that continues after the source of the sound stops, which is
caused by repeated reflections off of surfaces. Reverberation is similar to an echo, but not the same. The perception of a sound usually lasts in a person’s memory for only 0.1 second. With an echo, sound waves bounce off a surface distant enough that we notice a time delay between the original sound and the reflected sound. Reverberation, on the other hand, is perceived when the reflected sound wave reaches the listener’s ear in less than 0.1 second. The original sound and the reflected sound tend to combine together into one fuller, drawn out sound, like what you might hear when singing in the shower.
Sound waves will also bend around obstacles in their path. This bending is called diffraction.
In the field of architectural acoustics, engineers work to design a space that produces the best sound for its purposes, whether that be designing a concert hall with optimal acoustics or deadening a recording room from reverberation so the original sound waves are all that are picked up.
Audio engineers who work to record music use audio signal processing to control and adjust
these natural sound wave behaviors in order to produce a desired sound. The goal can be to make the recorded music sound as if it was played in a world renowned concert hall, or to make the music sound futuristic and strange. Being an audio engineer involves both artistry and technical skill. Each decision an audio engineer makes effects the final sound, making their contribution a musical one as well as a technical one. Audio engineers also work to create music and sound for television, movies, and video games.
Time delay effects involve combining the original audio signal with a delayed version of the same signal. These can create the sound of reverberation a listener would hear in a concert hall. Flanger and phaser effects use continuous, variable delays that can make a wooshing or synthesized effect. A time delay can also be used to create the sound of a chorus of voices singing from one recorded voice. By adding a signal with a constant delay to the original signal, making sure the delay is longer than a flanging effect but short enough that it isn’t perceived as an echo, the effect of a chorus of voices can be obtained. Adding a pitch shift to the altered signal can help as well.
A pitch shift effect shifts an audio signal’s pitch up or down. This can be used to create harmonies from one voice by combining a shifted vocal signal with the original signal. It can also be used for pitch correction, shifting wrong notes to the correct pitch.
Audio engineers can also use a time stretching effect to adjust the speed of an audio signal without affecting the signal’s pitch.
In post-production, audio engineers mix together multiple recorded tracks to create the
final recording and use equalization and audio level compression to create the cleanest, most balanced finished product possible. Equalization involves boosting certain frequency bands to produce a desired sound, allowing the engineer to adjust the tone quality of a recording. Compression involves reducing the dynamic range (reducing the volume of loud sounds and amplifying quiet sounds) of a sound to avoid unintended fluctuations in volume.
Engineers use mathematical algorithms, computers, electronics, and mechanics to control, alter, and manipulate sound waves in order to create the music that reaches us through recordings and live performances. Acoustical engineering is a field of science and artistry that impacts the sound and music we hear every day.