Frequency division and hearing difference of different frequency bands in the audio system
One of the core tasks of an audio system is to accurately reproduce the frequency components of a sound signal. The human auditory system is capable of perceiving sound waves in the 20Hz to 20kHz range, but the energy distribution in different frequency bands significantly affects the subjective listening experience. Understanding the frequency characteristics of different frequency bands and their auditory differences is crucial for audio equipment design, music mixing, and acoustic environment optimization.
Ⅰ. Low frequency band: the foundation of power and rhythm
① Extremely Low Frequency (20-60Hz)
Audio Characteristics: Sounds in this frequency range can feel powerful, deep, and resonant, determining the "spatial" and "impact" of a sound, such as thunder and the boom of a bass drum. The human ear can hardly hear it directly, instead experiencing vibrations (such as the thump of a subwoofer).
Excessive ultra-low frequency can make the sound appear muddy and mask details in other frequency bands. Insufficient ultra-low frequency can lack a "foundation."
Typical manifestations: Explosions in movie sound effects, the deep bass in electronic music, thunder, earthquakes, and other natural low-frequency effects.
Application Recommendation: Appropriate enhancement can create an immersive atmosphere, but avoid masking other frequency bands.
② Low Frequency (60-200Hz)
Audio Characteristics: Determines the depth and power of a sound. This is the fundamental component of sound, accounting for 70% of the total audio energy and a crucial component in expressing musical style. When properly balanced, bass creates a powerful, full, and mellow sound.
Excessive bass can produce a booming sound and a muffled timbre. Insufficient bass can make the music sound thin and thin.
Typical manifestations: The low end of bass drums, bass guitar, and cello. Excessive low frequency can create a "booming" feeling, while insufficient low frequency can create a "hollow" feeling.
Application Suggestion: Adjusting low frequency can alter the depth and impact of music.
II. Mid-frequency band: the soul of human voice and instruments
① Mid-Low Frequency (200-500Hz)
Audio Characteristics: This frequency band influences the warmth and richness of the sound. Chest resonance in the human voice (82-392Hz for male voices) and the midrange of woodwind instruments are concentrated here. A moderate boost can enhance warmth and presence, shifting the sound's position further back and increasing transparency.
Excessive boosting can result in a muddy sound.
Typical effects: Chest resonance in male vocals, the mid-bass of electric guitar, and the midrange of piano.
Application Suggestion: Adjusting this frequency band can optimize the distance of the human voice.
② Mid-Frequency (500Hz-2kHz)
This frequency range is the most sensitive to the human ear and dominates the core timbre of vocals and most instruments.
Overdoing it can be harsh, while underdoing it can make the sound hollow.
Typical applications: Vocals (especially female), lead melodies on guitar and piano, and telephone sounds.
Application Recommendations: This frequency range is central to tuning, requiring a balance between detail and naturalness.
③ Mid-High Frequency (2kHz-6kHz)
Audio Characteristics: Human hearing is most sensitive to this frequency range, which dominates clarity and penetration. Vocal sibilance, string overtones, and the higher harmonics of most instruments are concentrated in this range, determining the instrument's articulation and presence.
1-3kHz: The core frequency band for speech intelligibility; excessive boosting can be jarring.
3-6kHz: Boosting can enhance the texture of instruments (such as the metallic quality of a trumpet), but excessive boosting can cause auditory fatigue.
Typical manifestations: Vocal sibilance, violin highs, and distorted electric guitars.
Application Recommendation: When recording, attenuating 4-5kHz can reduce "microphone popping," while boosting 6kHz can enhance vocal presence.
III. High Frequency Band: The Magic of Detail and Spatial Space
① High Frequency (6-12kHz)
Audio Characteristics: Dominates the "resolution" and "air" of a sound's timbre, influencing the sense of space and detail. Overtones of percussion instruments like cymbals and triangles fall within this frequency range; boosting them can create a "golden" sound.
Excessive boosting can result in harshness or excessive sibilance (e.g., a "hissing" sound); insufficient boosting can result in a muffled sound.
Tuning Mistake: Commercial recordings often boost 8-12kHz to create a "high-fidelity" sound, but low-quality equipment can easily introduce background noise.
Typical Effects: Overtones of triangles, female vocals, and extended high notes in string instruments.
Application Recommendations: Appropriate boosting can improve "resolution," but avoid excessive distortion.
② Ultra-high Frequency (12-20kHz)
Audio Characteristics: The human ear perceives a sense of "air" and "gloss," but some people (especially the elderly) may not be able to hear this. This frequency band includes extremely high-frequency overtones (such as the tail notes of a flute). A moderate boost can enhance the spaciousness of the soundstage.
Excessive boosting can introduce noise, or make the sound appear hollow or unnatural; insufficient boosting can make the sound lack "liveliness."
Device Limitations: Ordinary headphones or speakers have difficulty reproducing frequencies above 15kHz, resulting in a loss of detail.
Typical manifestations: Ambient sound in recordings (such as the airiness of a recording studio), high-frequency overtones, and the "shimmer" of electronic sound effects.
Application Recommendations: A slight boost can increase transparency, but this should be adjusted based on device performance.
IV. Some commonly used important frequency points
①50Hz
As the lowest frequency range, 50Hz is crucial for shaping the kick drum's impact. Properly boosting this frequency band can enhance the physical vibration of the beat, infusing dance music with the fundamental energy that drives physical movement. However, it's important to note that all vocal tracks must completely cut this frequency band, as it often contains microphone breath noise (pops) rather than the actual vocal signal.
②70-100Hz
This frequency range, known as the "golden band" for shaping the depth of bass parts, determines the physicality of low-frequency energy. Bass and kick drums experience a masking effect in this frequency range. Applying simultaneous gain to both can reduce the kick drum's impact. It's recommended to use staggered processing (e.g., focusing on 80Hz for bass and 60Hz for kick drum) to create a clear low-frequency layer.
③200-400Hz
In audio processing, this frequency range is primarily used to enhance the woody resonance of snare drums, remove muddiness from vocals, add warmth to guitar tones, and enhance the crispness of cymbals and percussion through attenuation. Appropriate gain applied to the kick drum at 250Hz can reduce the sense of low-frequency pressure, a technique often used in fresh pop mixes.
④400-800Hz
Precise adjustments within this range can achieve the following effects: optimizing bass clarity and enhancing the warmth of toms. By applying boost or cut to specific frequencies within this frequency band, you can flexibly control the thickness of guitar tones and finely adjust the texture of the instrument.
⑤800Hz-1kHz
This frequency band effectively controls the density and dynamics of vocals, making them more penetrating. Appropriate boosting of this area can also enhance the impact and rhythmic grit of the kick drum, making it a core frequency band for shaping the signature kick drum sound in electronic dance music.
⑥1kHz-3kHz
This frequency range is often called the "metallic" because of its remarkable penetration. Boosting the 1.5kHz-2.5kHz range can enhance the sharpness of guitar or bass, adding a sharp edge to the performance. Moderately attenuating the 2kHz-3kHz range can effectively eliminate harshness in vocals, making singing smoother and less aggressive. Conversely, boosting this range significantly enhances the sharpness of vocals and piano. It's important to note that over-processing this frequency range can easily muddy the soundstage, but precise control can allow specific instruments to break through the mix, creating dramatic, localized tonal presentation.
⑦3kHz-6kHz
The acoustic characteristics of this frequency band exhibit remarkable tonal shaping capabilities. Specifically, the 3kHz region retains the characteristic metallic quality of mid- and high-frequency sounds. This "hard" listening experience stems from the fact that this frequency band concentrates the harmonic energy of musical instruments. Extending the frequency range to 6kHz, moderate gain not only enhances the intelligibility of vocal articulation but also imbues the guitar tone with a lush overtone sheen, particularly in strumming, where high-frequency harmonics create a silky halo effect. However, it's important to note that the 6kHz gain adjustment requires precise control; excessive boosting can result in sibilant overload or high-frequency harshness.
⑧6kHz-10kHz
This frequency band has a multi-dimensional impact on timbre. Specifically, a moderate boost in this frequency band can imbue vocals with a sugary sweetness, creating a transparent, breathy texture by highlighting breath-like details. It can also enhance the high-frequency overtones of guitar plucks, creating a contrast between the clear attack and the lingering overtones, creating a crisp texture like "crystal shattering."
⑨10kHz-16kHz
Boosting can enhance the brilliance of vocals and the high-frequency penetration of cymbals and percussion. However, it's important to first use a spectrum analyzer to confirm the presence of a valid sound source in this frequency range; otherwise, you'll amplify background noise rather than the musical signal. We recommend using a dynamic EQ to enhance the airiness of the 10-12kHz band and precisely enhance cymbal harmonics in the 14-16kHz range, while avoiding over-boosting that can cause harshness.