The Acoustics of How a Computer Hears Sound

The process of getting sound into and out of the computer is actually quite simple and is totally dependent on the science of sound, which we call acoustics.

Excerpted and adapted from Make Your Own Music: A creative curriculum using music technology (Backbeat Books) by Richard McCready. Reprinted with permission.

The process of getting sound into and out of the computer is actually quite simple and is totally dependent on the science of sound, which we call acoustics. Sound is made up of different speeds of vibrating air. Your ears are capable of feeling the vibrations in the air and telling your brain what you are hearing. The computer doesn’t have ears, so it needs some help understanding what sound is.

Here’s how it works: Your microphone is a delicate device that is able to feel the vibration of air and convert it to an electrical voltage. That voltage is then converted to digital data by an audio interface – like the PreSonus AudioBox USB – and is represented in your recording software as a waveform.

As you play back the waveform, the audio interface converts the digital data back to voltage. When this voltage is sent through speakers or headphones (which are actually just a very small pair of speakers that you wear on your head), the voltage is converted back to air vibrations that your ears then pass to your brain as sound. The audio interface is the essential link, and so a good quality audio interface is critical to good recording.

The microphone

The microphone is an example of a type of device we call a transducer – it takes one form of energy (sound waves) and converts it to another (voltage). A speaker is also a transducer, but it converts voltage to sound waves. Headphones contain tiny speakers, known as drivers, in each earpiece. In a simple way, a speaker is a backward microphone.

There is no doubt that we would have no such thing as recording without the invention of the microphone, which is generally credited to a Welsh physicist and musician named David Edward Hughes (1831–1900). Though he was born in Wales, in the United Kingdom, his family immigrated to the United States when Hughes was just seven years old. He was quite a prodigy, learning to play the harp by the age of six, and subsequently becoming a virtuoso pianist. He later became a professor of music at St Joseph’s College in Bardstown, Kentucky.

Hughes loved to tinker with electricity, and he created a number of telegraph and telephone-type devices. He invented the microphone in the mid-1870s as a device for converting the air vibrations created by the human voice into an electrical signal so that a human could be heard distinctly in a telephone conversation. His carbon microphone (as it was called) was essentially a transducer that changed sound to voltage.

When Hughes invented his device, he decided not to patent it. He wanted to give it to the world as a gift because he realized the enormous potential it would have in telephony. He probably had no clue that it would become so widely used in music and broadcasting today.

Emile Berliner and Thomas Edison both also created a type of carbon microphone quite independently, and both filed for the patent in 1877. There was a legal battle, and Thomas Edison was granted the patent, though he was not actually the first to come up with the technology.

All microphones use a capsule to convert sound waves to voltage. The type of capsule determines whether the microphone is dynamic, condenser, ribbon, or some other type. A condenser microphone operates via a small diaphragm that feels the vibration of air coming in and moves accordingly. The distance between the diaphragm and a static plate is then measured and transmitted by the microphone as voltage. The tiny amount of movement required to create the electrical signal means that condenser microphones are very precise in their recording quality, but are not capable of handling large sound pressure levels (very loud noises). They are somewhat fragile and should be handled carefully. Dust and dirt can render a condenser microphone less precise, so you should keep your microphone protected in its case whenever you are not using it.

Excerpted from Make Your Own Music: A creative curriculum using music technology, by Richard McCready. McCready was born in Northern Ireland and studied tuba performance, piano, and composition at the Royal Northern College of Music, Manchester, England. He began his teaching career at Frodsham School, a science and technology school in Cheshire, England. After immigrating to the US, McCready was awarded the Technology Institute for Music Educators Teacher of the Year Award in 2013, the 2013 Howard County (Md.) Music Educator of the Year Award, and the 2014 Maryland Outstanding Music Teacher Award. McCready was also a finalist for the Recording Academy Educator of the Year Award in 2015. In April 2013, School Band and Orchestra magazine featured a cover story on McCready’s work at River Hill High School. Earning two masters’ degrees from Towson University, one in tuba performance and one in vocal performance, McCready plays many musical instruments, but the focus of his teaching is music technology – an area in which is widely regarded as one of the outstanding innovators in the US.

Acoustics and the science of how a computer hears sound

The process of getting sound into and out of the computer is actually quite simple and is totally dependent on the science of sound, which we call acoustics.

The microphone

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