The frequency spectrum in audio is the complete range of frequencies that can be captured, reproduced, and heard — from the lowest sub-bass rumble at 20 Hz to the highest air and shimmer at 20,000 Hz (20 kHz). Understanding the frequency spectrum is foundational to mixing, mastering, EQ, and sound design. Every EQ decision you make is a decision about the frequency spectrum. Every mixing problem that involves a sound being "too muddy," "too thin," "too harsh," or "too bright" is a frequency spectrum problem. This guide covers every region of the frequency spectrum in depth.
The Human Audible Frequency Range
The human audible frequency range is approximately 20 Hz to 20,000 Hz (20 kHz). This range narrows with age — adults typically have reduced sensitivity above 15–16 kHz, and high-frequency hearing loss often begins in the mid-20s. Children can hear closer to the theoretical 20 kHz ceiling. The range below 20 Hz (infrasound) and above 20 kHz (ultrasound) is not directly audible but can be perceived as physical sensation at high amplitudes in the sub-bass region.
Musical instruments span different portions of this range. The lowest notes on a standard bass guitar reach approximately 41 Hz (low E). The lowest key on a concert grand piano sounds at approximately 27.5 Hz. The highest note on a soprano voice can reach 1,000–1,100 Hz. The highest frequencies in recorded music are the overtones, harmonics, and breath sounds from instruments that extend up to 15–18 kHz or beyond — not the fundamental pitches but the acoustic information that makes instruments sound realistic and three-dimensional.
Frequency vs pitch: Frequency is the physical measurement (cycles per second, measured in Hz). Pitch is the perceptual experience of frequency — what we hear as "notes." Concert A is defined as 440 Hz. Each octave doubles the frequency: A3 is 220 Hz, A4 is 440 Hz, A5 is 880 Hz, A6 is 1,760 Hz. This doubling relationship means the highest octave of the audible range (10–20 kHz) contains the same number of "musical notes" as the lowest octave (20–40 Hz) — but the frequencies are 500x higher. This has practical consequences for EQ: a 3 dB boost at 10 kHz affects a very different portion of the frequency spectrum than a 3 dB boost at 20 Hz, even though both represent the same amount of gain change.
Sub-Bass: 20–60 Hz
The sub-bass region contains the lowest audible frequencies — the deepest bass content that is felt as much as heard. On good studio monitors or subwoofers, sub-bass is a physical sensation in the chest and stomach rather than a clearly defined pitch. On laptop speakers or small Bluetooth speakers, sub-bass content is completely inaudible because the speakers cannot reproduce these frequencies.
What's in this range: The sub-harmonic content of bass guitar (the frequencies below the fundamental note that add depth and rumble), the low fundamental of large kick drums, the sub-bass of 808 bass in trap and hip-hop production, pipe organ pedal notes, bass synthesizer sub patches, and low-frequency room modes from acoustic instruments in rooms.
Mixing implications: Sub-bass content that isn't musically purposeful (low-frequency rumble from microphone handling, HVAC noise, proximity effect on vocal microphones) should be removed with high-pass filters. Sub-bass that is musically purposeful (808 bass fundamental, kick drum weight) should be controlled carefully because it eats headroom on the master bus without being audible on most consumer playback systems. A kick drum with excessive sub content will cause a limiter to react on every kick hit, limiting the perceived loudness of the entire mix without the sub being audible to the listener. Adding saturation to sub-bass content (808 bass, kick drum sub) generates harmonic content in the audible range — making the sub-bass content audible on small speakers that can't reproduce the fundamentals.
Bass: 60–200 Hz
The bass region contains the fundamental frequencies of most bass instruments and the low-end body that gives music weight, warmth, and physical energy. Getting the bass region right is the foundation of a professional-sounding mix — too much and the mix sounds muddy and indistinct; too little and it sounds thin and lightweight.
What's in this range: The fundamental notes of bass guitar (41–330 Hz for the standard four-string range), the kick drum's fundamental "thud" (60–100 Hz), the body of piano in the low octaves, the fundamental of floor toms, the body of male vocal chests in the low notes, and the fundamental of cello in its lower register.
Key frequency points: 60–80 Hz is the "boom" — the frequency that makes the kick drum feel powerful on a subwoofer. 80–120 Hz is the kick drum's main body — the most audible portion of the kick's low end on most monitoring systems. 100–150 Hz is where the bass guitar's fundamental sits in the low registers. 150–200 Hz is the transition between bass and low-mids — often called "warmth" when present in appropriate amounts and "muddiness" when excessive.
Mixing implications: The kick drum and bass guitar occupy the same frequency space and must be managed to avoid conflict. Common techniques: sidechain compression (the bass ducks when the kick hits), frequency carving (boost the kick's frequency in the bass and cut it in the bass guitar, or vice versa), and careful arrangement choices (don't have the bass guitar and kick playing the same note at the same time in dense arrangements). Most instruments that don't contribute musically to the 60–200 Hz range should be high-pass filtered to clear the bass region for the instruments that own it.
Low-Mids: 200–500 Hz
The low-mid region is the most problematic frequency range in most mixes. It accumulates mud — a thick, indistinct buildup that makes mixes sound congested and unclear. Almost every instrument contributes some energy here, and when multiple instruments are playing simultaneously, the cumulative low-mid content can overwhelm the mix's clarity and definition.
What's in this range: The upper body of bass guitar, the kick drum's "cardboard" character (around 300–400 Hz), the "warmth" of acoustic guitars, the boxiness of close-miked room reflections, the nasal quality of vocals (around 800–1,000 Hz at the top of this range), the fundamental of guitar power chords in lower positions, and the body of piano in the mid registers.
The problem: Every instrument has some energy in the 200–500 Hz range, and when they accumulate in a dense arrangement, the low-mid region becomes congested. A mix that sounds muddy and indistinct when everything is playing together often sounds fine when individual elements are soloed — because the mud is a collective problem, not an individual track problem. This is why frequency carving between instruments is essential: each instrument should have its own cleared space in the frequency spectrum so they can coexist without competing.
Mixing implications: High-pass filter everything that doesn't contribute musically to the low-mid region (hi-hats, overheads, synthesizer pads, backing vocals). On kick drum: a cut at 250–350 Hz removes the cardboard quality. On electric guitar: a cut at 300–400 Hz reduces the boxiness that accumulates from cab proximity. On vocals: a cut at 200–300 Hz reduces low-mid buildup without thinning the vocal's chest resonance. The goal is not to remove all low-mid content but to carefully manage which instruments contribute to this range and how much each contributes.
Mids: 500 Hz–2 kHz
The midrange is the most information-dense region of the frequency spectrum and the range where human hearing is most sensitive. The fundamental frequencies of most melodic instruments, the intelligibility of vocals, and the characteristic timbre of most acoustic instruments all live primarily in this range. It is also the most fatiguing range when excessive — a mix that's too mid-heavy sounds honky, harsh, or forward in an uncomfortable way.
What's in this range: The body and presence of lead vocals (500 Hz–2 kHz contains most of the vocal's character), the fundamental of acoustic guitar strums, the "twang" of electric guitar, the crack of snare drums, the warmth of piano in the middle octaves, the fundamental of most wind instruments, and the harmonics of bass guitar (which give bass notes their pitch definition and note-to-note distinction on smaller speakers).
Key frequency points: 500–800 Hz: "warmth" or "muddiness" depending on amount — this range gives instruments body and tonal richness. 800 Hz–1 kHz: the "honky" range — excessive content here makes voices sound nasal and instruments sound congested. 1–2 kHz: "presence" — this range defines intelligibility and forward projection. Vocals with reduced 1–2 kHz content sound recessed and distant; boosted, they sound forward and present.
Mixing implications: The midrange is where most mixing decisions about instrument separation and clarity are made. The key technique is carving: identify which instruments need midrange presence (the lead vocal, the lead guitar) and give them space by cutting the same frequency in competing instruments. A lead vocal that sounds buried in a guitar-heavy mix often needs both a boost in its presence range and a corresponding cut in the competing guitars at the same frequency.
Upper-Mids and Presence: 2–6 kHz
The upper-mid and presence region contains the frequencies most responsible for the intelligibility and perceived "forward" quality of sound. Boosts in this range make sounds cut through a mix; cuts make sounds recede. It is also the range where harshness and listener fatigue accumulate — too much energy here makes a mix tiring to listen to over extended periods.
What's in this range: The "presence" of lead vocals (the consonants and forward projection), the attack of acoustic guitar picking (the sound of the pick on the string), the "bite" and aggression of electric guitar distortion, the crack and snap of snare drums, the attack of piano keys, the harsh consonants of brass instruments, and the "click" of kick drum beaters.
Key frequency points: 2–3 kHz: attack and punch — the range that makes drums feel physical and guitars feel aggressive. Too much accumulation here produces a "pokey" quality. 3–5 kHz: presence and intelligibility — the most important range for vocal clarity. The "telephone EQ" character (bandpass filter emphasising 1–4 kHz) makes voices recognisable because this range contains most of the speech information. 5–6 kHz: harshness — the top of the presence range, where sibilance often peaks and where overprocessed or over-EQed material becomes fatiguing.
Mixing implications: The upper-mids require the most careful balance of any frequency region. Too little and the mix sounds dull and recessed — elements don't cut through. Too much and it sounds harsh, piercing, and tiring. Reference against commercial releases in the same genre frequently. The presence range is also where most mixing engineers' ears become desensitised during long sessions — take breaks and return with fresh ears before making final decisions about 2–6 kHz balance.
Highs and Air: 6–20 kHz
The high-frequency and air region contains the overtones, harmonics, and ambient information that make recordings sound detailed, open, and three-dimensional. Appropriate high-frequency content makes a mix "breathe" — it creates the sense of acoustic space and instrument detail that distinguishes a high-quality recording from a flat, lifeless one. Too much makes a mix harsh and bright; too little makes it dull and muffled.
What's in this range: The "air" of cymbals (the shimmery content above 10 kHz that gives cymbals their realistic acoustic character), the breath and detail of flute and other wind instruments, the overtone structure of plucked strings, the "sparkle" of a high-quality condenser microphone capturing vocal overtones, room sound and ambience (high-frequency reverb that gives acoustic spaces their sense of size), and the high-frequency content of electronic synthesizers and samples.
Key frequency points: 6–8 kHz: sibilance and brightness — this range contains the most problematic sibilance frequencies on vocals and the harshest content of overdriven guitars and cymbals. 8–12 kHz: "air" — the most musically valuable high-frequency range for most material. A gentle boost here adds openness and detail without harshness. 12–20 kHz: extreme air — content here is increasingly inaudible on consumer systems but contributes to the perceived quality of high-end monitoring. Boosting here on a mastering EQ adds a quality of "air" that is felt as much as heard.
Mixing implications: A gentle high-shelf boost (1–2 dB above 10–12 kHz) on the mix bus or on individual elements is one of the most common "finishing" EQ moves in professional mixing and mastering. The Neve 1073's characteristic high-shelf at 12 kHz is responsible for much of the "vintage" sound associated with classic rock recordings. High-pass the reverb returns aggressively below 200–400 Hz — reverb in the high-frequency range adds air and space; reverb in the low-frequency range adds mud.
Using a Spectrum Analyser
A spectrum analyser is a visual tool that displays the frequency content of an audio signal in real time — showing which frequencies are present and at what level. Learning to use a spectrum analyser effectively improves mixing decisions but must be balanced with listening — the analyser shows what's there, not what sounds right.
What to look for: A balanced mix typically shows a gradual high-frequency rolloff (the curve drops from left to right, higher frequencies are lower level than low-mid frequencies) — this is normal and expected, matching the equal-loudness curves of human hearing. Peaks that stick up significantly above the general curve indicate frequency buildups that may need attention. Broad flat regions in the high frequencies indicate insufficient air. A "waterfall" (sustained energy at specific frequencies) indicates resonances.
Reference comparison: Load a commercial reference track and compare its spectrum to your mix side by side. The reference's spectrum is not a target to exactly match but a guide to the approximate tonal balance of successful recordings in your genre. Systematic differences between your mix's spectrum and the reference often identify the source of tonal problems.
The limitation of analysers: Frequency spectrum analysis shows level by frequency but not the interaction between frequencies over time, the stereo image, or the dynamic behaviour of the mix. A mix can look balanced on an analyser and sound wrong because of a frequency that's at the right average level but has problematic transient peaks. Always make final decisions with your ears, not your eyes.