The most important factor that determines the sound characteristics of a microphone: What effect does the frequency response of a microphone have on the quality of sound?

What is microphone frequency response?

A microphone responds to mechanical waves (acoustic energy) at its diaphragm and converts them into an audio signal (electrical energy). The frequency response defines the range of sound a microphone can reproduce and how its output varies within that range. Frequency response refers to the microphone’s sensitivity at different frequencies, indicating its ability to capture sound signals at different frequencies. It is typically measured in Hertz (Hz), and the frequency response range is usually between 20 Hz and 20 kHz.

Frequency response is a crucial factor in determining the characteristics of microphone sound. It is represented graphically by a response curve. The two most common types of frequency response are flat response and shaped or customized response.

Sound waves are complex and typically consist of a series of frequencies and amplitudes. The frequency response of a microphone represents its sensitivity to different frequencies, indicating which frequencies it is more or less sensitive to. However, the frequency response range can sometimes be misleading, so it’s best to rely on frequency response graphs to truly understand a microphone’s frequency response.

Achieving a completely flat frequency response is challenging, so some minor variations are normal. Nonetheless, if a microphone’s frequency response remains relatively flat across most of the frequency range, it can be considered “flat.” Microphones with some variations are often categorized as “flat/colorful,” indicating that they may have roll-offs in the high or low frequencies.

Choosing a microphone with a flat/colorful frequency response is often preferred because it can accurately and naturally capture sound. Such microphones can produce more realistic and accurate sound effects.

Frequency Response of the Human Ear:

Yes, our ears also have a frequency response!

As we discussed, the outer limits of human auditory perception are around 20 Hz on the low end and 20,000 Hz on the high end.

We have developed sensitivity in the range of 2,000 Hz to 5,000 Hz. This is the range of vocal clarity for human speech. As we discussed earlier, vocal microphones benefit from a boost in this range.

As the spectrum gets lower towards 20 Hz, we become less sensitive to SPL levels.

In fact, we feel these sub-bass frequencies (20 Hz – 60 Hz) more than we actually hear them.

On the high end of the spectrum, as we age, we slowly lose sensitivity and repeatedly damage our hearing.

For example, due to spending a lot of time playing music in loud bands and attending loud performances, I personally struggle to hear anything above 16,500 Hz… Protect your ears!

≤ 60 Hz = Sub-bass
This is felt more than heard in this frequency range (refer to the Fletcher-Munson curve). Most instruments and sounds lack information in this range.

Pay particular attention to the sub-bass frequency response of kick drums, bass guitar amplifiers, and large diaphragm microphones.

60 Hz – 250 Hz = Bass
This is where most of the “musical” bass information resides. The fundamental frequencies of many instruments are in this range, including the majority of human vocals!

250 Hz – 500 Hz = Low-mid
This range contains the strong harmonics of low-frequency instruments and the fundamental frequencies of some high-frequency instruments. Overemphasis in this frequency range can make a microphone sound “muddy,” while underemphasis can make it sound too thin.

500 Hz – 2 kHz = Midrange
The human ear becomes more sensitive in this range. It includes the weak harmonics of low-frequency instruments and the strong harmonics of high-frequency instruments.

2 kHz – 4 kHz = High-mid
This is the range where the human ear is most sensitive. A microphone that is significantly boosted or attenuated in this range will not accurately reproduce the timbre of the sound.

4 kHz – 6 kHz = Presence
If a microphone is sensitive in this range, it can enhance the sense of “presence” in the sound or potentially make it sound harsh. There’s a fine line here.

If a microphone’s frequency response drops in this range, it can make the source sound transparent or farther away than it actually is.

≥ 6 kHz = Brightness
Many dynamic microphones roll off in the “brightness” range at some point, even though their rated capture frequency may go up to 20 kHz.

This range is part of why condenser microphones tend to sound more “hi-fi” overall. They excel at picking up the frequencies in this range, including all the higher harmonics of the sound and the “air” and “sparkle” (my technical terms).

Ribbon microphones, on the other hand, often gently roll off in the brightness band, resulting in a reproduced sound that is “warm.”

To better understand the complex frequency response of human hearing, look at the Fletcher-Munson curve:

In general, the curve above demonstrates the relative frequency sensitivity of human hearing.

In the graph, you will notice several lines associated with different “phon” values.

“Phon” represents the level of perceived loudness. The lower the “phon” line, the more sensitive we are to the sound pressure level of a particular frequency.

0 phon represents the threshold of audibility, which is the minimum sound pressure level we can hear.
120 phon represents the threshold of pain, beyond which the sound pressure level can cause auditory damage.

At the low-frequency end (20 Hz), we require higher sound pressure levels to truly perceive the sound. However, at 4 kHz frequency, we are highly sensitive to changes in sound pressure, even small variations can be detected.

What is the difference between the impact of flat frequency response and shaped frequency response on sound?

Flat response microphones are equally sensitive to all frequency ranges, so their response curve is essentially a flat line. A flat response microphone can accurately reproduce the sound source with little or no change from the original sound. This is great for recording instruments or sound effects, but flat response microphones often sound subpar. Shaped response microphones are more sensitive to certain frequency ranges than others. Their response curve has peaks and valleys. Many shaped response microphones are less sensitive to low frequencies, which reduces the pickup of handling noise and stage rumble when the microphone is mounted on a stand. Shaped response microphones typically also have an enhancement in the mid-high frequency range, often between 3,000 and 6,000 Hz. This is called presence boost, and it enhances the clarity or “punch” of the sound and instruments. Ideally, whether a microphone has a flat or shaped frequency response, the frequency response curve should be relatively smooth line. If there are many sudden peaks and valleys, the microphone’s sound may not be very natural and it may be more prone to causing feedback in a PA system. Some microphones allow for adjustments to their frequency response to suit different applications. The most common adjustment is the low-frequency roll-off control to reduce the pickup of room rumble, and enhancing the mid-high frequencies to improve speech clarity.

If your voice is higher and thinner, there will be more energy in specific frequency ranges. If your microphone has a faster response in that range, it will enhance the pitch and timbre. In other words, it will emphasize the higher tones and “weaknesses” in your voice. This may steer you away from microphones that respond in this way. Ideally, we want to faithfully reproduce our voice as voice actors.

In fact, high-quality microphones may initially sound a bit “plain” because they don’t emphasize any specific parts of the frequency spectrum. Audio engineers often like this because all the audio information is there, and they can adjust it as needed. Shaped response microphones are suitable for audio applications that require adjustments and optimization in specific frequency ranges. They can enhance the clarity, presence, and punch of the audio to meet the needs of different situations. They can improve the clarity and presence of music and vocals by boosting the mid-high frequency range. Shaped response microphones are also suitable for speeches, conferences, lectures, and broadcasting. Their frequency response is usually optimized to improve the clarity and intelligibility of speech. In professional recording studios, shaped response microphones are commonly used to record vocals, instruments, and other sound effects. Their response characteristics can help engineers capture the desired tone and audio characteristics. Shaped response microphones are also widely used in the broadcasting and television industry. They can provide clear voice recordings and deliver good results in TV shows, radio programs, and news broadcasts.