Technology Thursday: What you need to know about microphones – part 3

Part one and part two of this series covered the basic types of microphones singers will encounter and how those microphones respond to the amplitude of the voice. This final post of the series discusses how microphones respond to the frequencies of the voice.
Frequency Response

Frequency response is a term used to define how accurately a microphone captures the audio spectrum of the acoustic signal. A “flat response” microphone captures the acoustic output with little to no alteration of the audio spectrum. Microphones that are not designated as “flat” have some type of attenuation or boost across one or more bands of frequencies within the audio spectrum.

When using a microphone with a polar pattern other than omnidirectional (a pattern that responds to sound equally from all directions), the user may encounter frequency response fluctuations in addition to amplitude fluctuations. Cardioid microphones in particular are known for their tendency to boost lower frequencies at close proximity to the sound source while attenuating those same frequencies as the distance between the sound source and the microphone increases. This is known as the “proximity effect.”

Let us compare the frequency response curves of two microphones, the Shure SM-58 and the Oktava 319. The Shure SM-58 microphone attenuates or “cuts” the frequencies below 300 Hz and amplifies or “boosts” the frequencies in the 3-kHz range by 6 dB, the 5-kHz range by nearly 8 dB, and the 10-kHz range by approximately 6 dB (Figure 18–10). The Oktava 319 microphone cuts the frequencies below 200 Hz while boosting everything above 300 Hz with nearly 5 dB between 7 kHz and 10 kHz (see the figure below).

In practical terms, recording a bass singer with the Shure SM-58 would drastically reduce the amplitude of the fundamental frequency with a strong amplitude peak in the singer’s formant zone. In contrast, the Oktava 319 would produce a slightly more consistent boost in the range of the singer’s formant without reducing the amplitude of the lower frequencies. Either of these options could be acceptable depending on your needs, but the frequency response must be considered before making the recording.

Implications for the Singer

The frequency response of a microphone can significantly alter the balance of forward placement and fundamental of a singer’s voice (called the singing power ratio). If a microphone significantly boosts the amplitude of the forward placement zone, it will alter the singing power ratio, thus altering our perception of the singer’s voice. If a singer is struggling to find a reliable technical approach for boosting the upper frequencies of his or her voice, a microphone that boosts those frequencies could be beneficial. However, if a singer has an abundance of acoustic power in the upper frequencies of his or her voice, a microphone that boosts those frequencies could artificially alter the singing power ratio in a manner that would cause the voice to be perceived as overly bright and perhaps harsh (Omori, Kacker, Carroll, Riley, & Blaugrund, 1996).

Singers should take the time to audition numerous microphones to see which one best complements their voice. Set several microphones in a row with the same settings at the soundboard and sing the same excerpt on each microphone. If possible, make a recording and listen for changes in the timbre from microphone to microphone.

Microphone Technique

Just as there are techniques that improve singing, there are also techniques that will improve microphone use. Understanding what a microphone does is only the first step to using it successfully.

Practicing With a Microphone

The best way to learn microphone technique is to practice with a microphone. Using a dynamic microphone, try the following:

• Position the microphone directly in front of your mouth, no further than 1 cm away. Sustain a comfortable pitch and slowly move the microphone away from your lips. Listen to how the sound quality changes. When the microphone is close to your lips, you should notice that the sound is louder and has more bass response. As you move away from the mic, there will be a noticeable loss in volume and the tone will become brighter.
• Next, try sustaining a pitch while rotating the handle down. You should notice that the sound quality changes in a similar fashion as when you moved the microphone away from your lips.
• Now try singing breathy with the microphone close to your lips. How little effort can you get away with and still sound good?
• Try singing bright, at a medium volume level, with a closed mouth and spread lips with the microphone placed approximately 1 to 3 cm from your mouth. In this position, you should be able to create aggressive sounds without over-singing.
• Next, cup both of your hands around the microphone and then sing into your hands. Try using a vocal fry in this position and experiment with death metal–style sounds. You should notice that the cupping of your hands increases the bass response and helps boost your vocal power without excess effort.
• Also, experiment with variations in your diction. Because the microphone amplifies everything, you may need to under-pronounce some consonants when singing on a microphone.