Monthly Archives: March 2020

Microphones – “Good” and “Bad”

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As you will see in the next few posts, there are many ways to classify microphones. You can categorize them by type: dynamic, ribbon, and condenser. You can also group them by directionality: omni, cardioid, and figure 8. Some people would also group them as “good” and “bad.” Of course, we all want good microphones and would like to avoid the bad ones, but the answer to the question is extremely subjective.

Usually, the question implies, “What is the cost of” a good microphone. The answer to that is $100.  The Shure SM57 is probably the most popular microphone used in recording studios. It appears in almost every studio’s mic locker, and usually in multiples. The SM-57 retails for around $100. The answer is also $3500. This is the cost of a Neumann U87, which appears in all major studios and has been used on countless hit songs. So, it isn’t about price.

Astatic Corporation in Conneaut, Ohio, built a little green bullet-shaped crystal microphone in the 1940s called the JT-31. Crystal microphones are rarely used today because of their poor frequency response and distortion. The JT-31 was used as a Public-Address and communications microphone. It sounded terrible by today’s standards but became extremely popular among blues harp players. It was lightweight, cupped in the hands easily, and distorted the sound (in a pleasing way) when played through a tube amplifier. So if you are a harmonica player, it is a good microphone. So, “good” depends on your use.

The Neumann U87AI is a $3500. microphone. It has a self-noise level of 12 dB(A). The $250. RØDE NT1, which sells for about $250. has a self-noise of only 4.5 dB(A), which is 7.5 dB better than the Neumann. This is a significant amount. If you need a quiet microphone, buy the RØDE. “Good” depends on what specification is essential to you.

I could go on here, but I hope you can see that what is “good” is very subjective.  Much depends on what your needs are. In general, microphones of any type, condenser, dynamic, and ribbon, at the very bottom of the price range, have compromised build quality and poor quality control.  But that changes quickly as the microphones go up in price. Because of modern manufacturing methods and the precision of computer-controlled machines, the cost of manufacturing a great microphone has diminished considerably. Plus, the economies of scale kick in as the home recording market has exploded in the past 25 years, and the volume of quality recording microphones has increased exponentially as well. As an electrical engineer, I don’t see anything in the build or components of most microphones that justifies a price of over $1500.

The differences in quality between a $500. microphone and a $3500. microphone are subtle. But there is intangible value in knowing you are buying the best. There is considerable psychological value in using the model of microphone that studios have used for years to record many classic hits.  And what is that intangible value? Significant since many people are willing to acquire microphones for over $1500.

Consider this, a $40. crystal-controlled Timex watch is four times as accurate as a $3500. Rolex. But some people gladly spend for the Rolex because it offers them something more than the ability to keep precise time.

Microphones Operate in a 3-Dimensional Space

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3-Dimensional Microphone

Microphones are arguably the most critical piece of equipment in the studio because they pick up the vibrations in the air that we know as sound and convert it to an electrical signal that you can record manipulate and reproduce. They are the interface between the physical world of sound and the world of recorded audio. Any discrepancies in the fidelity of the microphone become part of your recording.

 It is essential to understand that microphones operate in a 3-dimensional space. It is also important to realize that there are no point sources of sound and that the sources we record have a physical size. The sound radiates from that whole physical source, and different sounds may radiate from different parts of it.

Consider an acoustic guitar. The guitar has a physical size of about 3 feet long, a foot and a half in width, and a thickness of six or more inches. Sound radiates from the whole body of the guitar, a different sound comes out of the soundhole, the strings radiate another sound, where the fingers pluck or strum the strings is one more sound, and the fingers of the other hand sliding along the fretboard produce a separate sound.

Imagine the microphone as a mixer that combines all of these sounds. Depending on the characteristics of the microphone, its directional pattern, and how we position it in 3-D space, it picks up a different mix of all these sounds. The signal coming out of the microphone cable is one-dimensional. Thus, the output of the microphone is the sum of all of those different sounds. They are processed as a single sound by any inline processing or in the DAW.

But we’re not done yet; our imaginary mixer has additional channels! Besides the different sounds coming from the guitar, there are sound reflections off of the floor and the ceiling. There’s sound reflected from the studio walls, noises occurring in the studio, and the sounds of the guitar player breathing and moving around. And if other instruments are being played at the same time, there is leakage from those. All of these sounds mix with the music from the guitar.

You can get more room sound by moving the microphone away from the guitar or less room sound by moving it closer. You can change the sound of the guitar by pointing your microphone at different parts of the guitar. And your choice of microphones affects the balance of all of these sounds. This whole mix then comes out of the microphone cable as a single monaural signal.

This signal coming out of the microphone cable is one-dimensional, a final mix. You can’t change the balance of the mix in post-production. Any effects or processing that you do affects that whole mix of guitar and room sounds. That is why microphone choice and positioning are so critical.