Equalising for Spectral Character
March 20, 2025
Equalising for Spectral Character
Five Core Priorities for Today’s Recording Engineer
- Frequency Range – Modern audio equipment is capable of capturing an incredibly wide spectrum of sound – nearly 10 octaves, covering frequencies from 20 Hz up to and beyond 16,000 Hz. (Beyond 20kHz in todays recording world) However, both physical limitations and creative decisions often require careful management of this range. Equalisation (EQ) plays a crucial role in overcoming these challenges, helping engineers balance and shape the frequency content to achieve a natural and impactful sound.
- Rhythm and Groove – Rhythm forms the backbone of any musical performance, but it’s not just the performer’s job to deliver it effectively. Engineers play a key role in maintaining and enhancing rhythmic feel by managing the balance of low and midrange frequencies, especially in the bass and kick drum. Through thoughtful mic placement, level control, and EQ, the engineer ensures the rhythm section drives the track with clarity and punch.
- Variety and Interest – Our ears are naturally drawn to variety and contrast. A great mix maintains listener engagement by presenting a balanced spectrum, where each sound source complements the others. Using EQ, panning, and dynamics processing, the engineer can create space and contrast in the mix, giving each element its own place while maintaining overall cohesion.
- Dynamics and Energy – Dynamic range – the difference between the quietest and loudest parts of a track – is key to emotional impact. (Something clearly missing in many modern mixes!) While the human ear can perceive an enormous dynamic range, modern recording systems typically manage a maximum of around 60 dB. (Well and truly beyond 100 dB today) The engineer’s job is to control dynamics through careful gain staging, compression, and EQ, ensuring the energy of the performance is preserved without causing distortion or listener fatigue.
- Spectral Balance and EQ Control – Equalisation isn’t just a technical process; it’s an art form. Spectral control means shaping the tonal balance of a mix, boosting or cutting specific frequency ranges to enhance clarity, presence, and emotion. By fine-tuning how each element sits within the frequency spectrum, the engineer creates a mix that feels balanced, dynamic, and engaging – bringing out the best in the performance and ensuring it translates across playback systems.
This article is drawn from information originally published in a 1960s Langevin catalogue, yet it offers valuable insights that remain highly relevant for making effective EQ adjustments in modern audio production.
Octaves and Frequencies
VERY LOW BASS - POWER RANGE
The 16 to 64 Hz range represents the threshold of physical sensation, where sound is often felt more than heard. This is where deep, low-frequency sounds like wind noise, room ambience, and distant thunder reside. In the upper part of this range, just below 32 Hz, the lowest fundamentals of instruments such as the piano, organ, and harp can be found. Research by J. C. Sierenberg suggests that the human ear retains a strong memory of these extreme low frequencies; they don’t need to occur often within a musical passage to create a lasting impression of power and depth. Even a brief appearance can balance the overall tonal spectrum and prevent higher frequencies from dominating the sound.
Harvey Fletcher’s studies on human hearing demonstrate that our sensitivity to these low frequencies decreases significantly at lower listening volumes. To maintain the perceived balance, playback systems often need to boost this range dramatically – by as much as 10, 20, or even 30 dB, equating to a gain increase of up to 1,000 times.
Careful management of sub-bass frequencies is critical. Without it, issues like stage rumble and environmental noise, such as traffic outside the studio, can intrude—something famously problematic in New York’s Studio A. Overemphasising these frequencies, especially when using velocity-sensitive ribbon microphones, can lead to a muddy, indistinct sound. It’s just as important to attenuate this part of the spectrum when necessary as it is to boost it, ensuring clarity and control in the low end of a mix.
1st to 2nd
Octaves
16 - 64Hz
BASS - RHYTHM AND MUSICAL FOUNDATION
Most of the deep, low-frequency tones produced by drums and pianos fall within this range. This is where you’ll find the core fundamentals of the rhythm section in a dance orchestra and the sonic foundation of virtually all musical arrangements.
Leopold Stokowski once remarked, “If I had a thousand bass viols I could use them all!” As exaggerated as that sounds, the concept isn’t entirely far-fetched. Large numbers of string instruments, supported by percussion, can produce powerful, resonant themes – especially when combined with horns and basses playing in unison. That said, the acoustic reality is that adding 1,000 bass viols would only increase the overall sound level by about 1 dB. In practical terms, even eight bass viols in the pit of a large orchestra are enough to create a rich, balanced low-end foundation. In orchestration and mixing, controlling energy in the 100 Hz range is key to maintaining that depth and weight.
Directional microphones introduce another consideration: the proximity effect. This phenomenon causes a significant low-frequency boost when the microphone is placed very close to the source, particularly with vocals. To avoid an unnatural bass-heavy sound in dialogue or close-miked sources, applying low-frequency attenuation helps restore clarity, natural tone, and proper balance in the mix.
3rd to 4th
Octaves
64 - 256Hz
MID-RANGE
The human ear is highly sensitive in the midrange, and most modern recording and playback systems handle this part of the spectrum well. However, balance is crucial. If the 6th octave – roughly between 1 kHz and 2 kHz – is boosted too much relative to the surrounding frequencies, the result can be a harsh, horn-like quality. Excess emphasis in the 1,000 to 2,000 Hz range often introduces a “tinny” or nasal sound that can be fatiguing to listen to.
The core fundamentals of most musical content lie both above and below middle C, typically spanning from around 128 Hz to 512 Hz. Since many instruments are rich in their first overtones, a significant amount of the overall sound energy extends up to about 2,500 Hz. For musicians, audio engineers, and listeners alike, prolonged exposure to an overly pronounced midrange can lead to listening fatigue. To counter this, it’s common practice to slightly attenuate frequencies in the 5th, 6th, and 7th octaves – by around 5 dB – creating a smoother, more natural listening experience without compromising clarity or presence.
5th, 6th and 7th
Octaves
256 - 2048Hz
LISPING QUALITY
Frequencies around 3 kHz have a strong impact on the human ear. At high listening levels, the point of greatest ear sensitivity often shifts downward from 5 kHz to around 3 kHz. This is one reason why many public address systems are designed with a pronounced presence in the 3 kHz range – to maximise intelligibility, especially in noisy environments.
However, when lower-level signals are overly boosted at 3 kHz, the sound can take on a harsh, “lisping” quality. This excessive focus can make it harder to distinguish certain consonant sounds, particularly labials like “m,” “b,” and “v,” which can become unclear or masked.
In many mid-range, lower-fidelity systems, a prominent peak around 3 kHz tends to mask important speech recognition frequencies, as well as sounds in the range above 4 kHz. This loss of upper clarity can dull brilliance and reduce overall definition. Without proper attenuation, the result is often listener fatigue, as the ear unconsciously strains to make sense of the compromised sound. Managing this frequency range carefully is crucial to maintaining clarity, balance, and a comfortable listening experience.
7th and 8th
Octaves
3kHz
PRESENCE RANGE
For male voices, the frequency range that most affects speech clarity typically falls between 3,000 and 6,000 Hz. In female voices, the fundamental frequencies are generally about an octave higher, and their consonantal clarity is usually concentrated between 5,000 and 8,000 Hz. However, the upper end of this range can approach areas where human hearing sensitivity starts to decline. Additionally, the overall frequency range of a woman’s voice is about half that of a man’s, stimulating fewer auditory nerves, which can make it slightly less prominent or more difficult to distinguish in certain contexts.
In wide-frequency material – particularly in vocal performances – much of the tonal clarity and presence is found around the 5 kHz range. Voices that are strong and rich in harmonic content at this frequency tend to sound clearer, fuller, and more pleasing. This is especially true for male opera singers, who often benefit from a boost around 5 kHz. Female voices, while sometimes less prominent in this area, can also be enhanced by increasing presence in this range, which helps improve definition and reduce listening fatigue. Boosting around 5 to 8 dB at 5 kHz can enhance articulation, bringing greater clarity to consonants like “t,” “s,” and “sh.” This adjustment can also give the impression of increased level without adding harshness, thanks to the natural transparency of this frequency range.
Conversely, attenuating the 5 kHz region on instruments can create a more transparent, open sound when done carefully. Many engineers working with electronic equalisation have described this approach as creating a “saddle” in the frequency response – dipping the 3 kHz region slightly and then easing into a boost at 5 kHz. This technique can help balance clarity and smoothness in both vocal and instrumental recordings.
8th and 9th
Octaves
4.75kHz to 5kHz
BRILLIANCE
Unvoiced consonant sounds – such as those produced by the teeth, tongue, and lips – occupy the higher frequencies, typically around the 10 kHz range. These frequencies contribute relatively little to the overall energy of speech, accounting for less than 2% of its total power, yet they play a critical role in providing clarity and brilliance. The same principle applies to musical instruments, particularly percussion, where the highest harmonics add definition and presence. To accurately capture these high-frequency details – regardless of microphone placement or inherent sensitivity in the upper register – having the ability to boost this range smoothly is often beneficial.
However, some microphones, particularly those with smaller diaphragms (around half an inch in diameter), may require the opposite approach. In these cases, particularly when recording speech or vocals, the extension of high-frequency response can exaggerate certain sounds. This phenomenon relates to the “baffle effect,” described by Mueller, Black, and Davis in 1934, where additional sound pressure builds on the microphone diaphragm, increasing output by as much as 9.8 dB over a significant frequency band. The primary frequency affected is closely tied to the diaphragm’s physical dimensions. For example, a diaphragm size equivalent to 5% of a given wavelength corresponds to approximately half the wavelength of 9 kHz.
If the microphone is not properly damped, this rise in response can lead to excessive sibilance, resulting in harsh, unnatural “ess” sounds during speech recording. Interestingly, in certain musical contexts – such as Latin percussion featuring instruments like gourds and rattles – this same high-frequency boost can enhance clarity and detail, producing an engaging and lively sound when handled appropriately.
9th and 10th
Octaves
6.5kHz to 16kHz
Effective equaliser adjustments begin with a clear understanding of the fundamental frequencies where each instrument or vocal naturally sits within a mix. By identifying these key frequency ranges, you can make more informed decisions when shaping the tonal balance, enhancing clarity, and ensuring each element has its own space in the overall sound. We hope this guide provides you with practical insight and helps you develop more controlled, professional-sounding mixes.
