What does the A in dBA mean?

It stands for A-weighting, a standard filter that turns down very low and very high frequencies to roughly match how our ears respond to everyday, moderate sounds. A reading in dBA is a sound level with that filter applied.

Is dBA or dBC better?

Neither is better in general. dBA is the standard for most noise guidance, workplace limits and neighbor complaints. dBC is more useful when bass matters, such as music, home cinema or a thumping subwoofer next door. Taking both and comparing them tells you how much low-frequency sound there is.

Why does my decibel app read higher than my friend's?

There are many possible reasons: different phones, cases, positions and distances. A common one is weighting. If one app shows unweighted dBZ and the other shows dBA, the dBZ number will often be higher, especially near fans, traffic or anything with a low hum.

What is Leq in decibels?

Leq means equivalent continuous sound level. It is the single steady level that would carry the same total sound energy as the changing noise you measured. It is the best one-number summary of how loud a period of time was.

Should I use fast or slow response?

Use slow for steady noise like traffic or a fan, because it gives a calmer number that is easier to read. Use fast when you care about short sounds like door slams or drum hits. Either way, the Leq and max over a session are often more useful than the live number.

dBA vs dBC vs dBZ: which decibel weighting to use

One of the most common complaints we found in reviews of other decibel apps was that a quiet bedroom read far louder than it felt. Often it was not the mic. The app was showing unweighted decibels, dBZ, without saying so, and counting the low hum of a fridge or the air conditioner that our ears mostly ignore. That one detail made a lot of people distrust their readings. It is also why Loudmark is built around dBA. Here is what those letters mean.

What weighting is

Our ears are not equally sensitive to all pitches. At everyday volumes, we hear the middle of the range, around voices, much more easily than deep bass or very high squeaks.

A microphone does not care. It picks up a deep rumble just as readily as a voice. So a raw reading can include a lot of sound that you hardly notice.

Weighting is a standard filter applied to the reading before it is shown. It turns some frequencies down so the number lines up better with a particular purpose. The letter after “dB” tells you which filter was used.

dBA: weighted like everyday hearing

A-weighting turns down low frequencies quite a lot and very high ones a little. The result roughly follows how our ears respond to quieter, everyday sounds.

Use dBA for:

Room noise, offices, classrooms and traffic.
Neighbor noise complaints.
Hearing risk. NIOSH and OSHA workplace limits are set in dBA, and so is the WHO guidance on night noise in bedrooms.
Comparing your reading with charts of everyday sounds, like our decibel chart.

If you only use one setting, use this one.

dBC: flatter, and counts the bass

C-weighting is much flatter. It trims only the very lowest and very highest frequencies, so it keeps most of the bass. It was designed with louder sounds in mind, where our hearing becomes more even across pitches.

Use dBC for:

Loud music, especially with heavy bass, at gigs, clubs or home cinemas.
A subwoofer or bass line coming through a wall or floor.
Peaks. Peak readings are often given in dBC.

A handy trick: measure the same sound in both dBA and dBC. If dBC is much higher than dBA, there is a lot of low-frequency energy. That is useful to note in a complaint about thumping music, where the dBA number alone can make the problem look smaller than it feels.

dBZ: no weighting at all

Z-weighting means zero weighting. The meter counts everything across its range equally, within the limits of the microphone.

Use dBZ for:

Technical work, like acoustic testing or comparing equipment.
Seeing the full picture when you will analyze the sound later.

For everyday questions, dBZ can mislead. A quiet room with a fridge, a fan or distant traffic may read noticeably higher in dBZ than in dBA, because of low rumble you hardly hear. That is the most likely reason a free app that shows plain “dB” seems to read high.

Quick guide: which one to pick

Is this about noise in a home, office or street? Use dBA.
Is this about hearing risk? Use dBA.
Is bass the problem? Take dBA and dBC, and write down both.
Is this a technical measurement? Use dBZ, alongside the others.
Not sure? Use dBA.

Whatever you choose, write the letter down with the number. “65 dB” on its own leaves people guessing. “65 dBA” does not.

Fast and slow response

Weighting is about which pitches count. Response time is about how quickly the meter reacts.

Fast follows changes every 1/8 of a second. It catches short sounds like a door slam, a clap or a drum hit, but the number jumps a lot.
Slow smooths the reading over about 1 second. It is calmer and easier to read for steady noise like traffic, a fan or an engine.

Neither changes the average much over a longer session. They mostly change how the live number moves, and how high the max goes, since fast catches short peaks that slow smooths over.

Leq, explained simply

Real noise goes up and down. Saying “it was 70 dB” is not quite right if it swung between 55 and 85.

Leq, the equivalent continuous level, solves this. It is the single steady level that would carry the same total sound energy as everything you measured. You will often see it written as LAeq when it is A-weighted.

A few things to know:

Loud moments count for more. Because decibels are on a log scale, a few loud bursts can pull the Leq up a lot more than you might expect.
Longer is better. Measure for at least 30 seconds for a quick check, and longer for noise that comes and goes.
Report min, Leq and max together. The min shows the background, the Leq shows the overall level, and the max shows the worst moments.

For step-by-step tips on taking a steady reading, see how to measure decibels on iPhone.

A note on phone microphones

Phone mics are made for voices. They tend to be less sensitive to very deep bass, and iPhone mics typically top out somewhere around 95 to 100 dB. So a phone’s dBC and dBZ readings of bass-heavy or very loud sound may be lower than a real sound level meter would show. Calibrating against a real meter helps your readings line up, but it does not turn a phone into a certified instrument.

When the letters matter for a complaint

If you are recording noise for a landlord, HOA or council, the weighting is part of the evidence. Use dBA as your main figure, because that is what most guidance and many local rules refer to. Add dBC if bass is the issue. Note the time, how long you measured, and the Leq and max. Our guide on how to record noise from neighbors as evidence covers the rest of a good noise diary.

Where Loudmark helps

Loudmark is our decibel meter for iPhone. It needs iOS 26. We built it so the weighting is never a mystery.

A live dBA meter, with dBC and dBZ available when you need them.
Fast (1/8 s) or slow (1 s) response.
Min, average (Leq) and max for every session, with a scrolling graph.
A plain comparison like “As loud as a vacuum cleaner”.
Calibration of plus or minus 20 dB in 0.5 dB steps, and a “near the mic limit” note when readings approach what an iPhone mic can handle.

All of that is free, along with one 85 dB alert and widgets. Loudmark Pro adds an evidence camera, overnight recording, PDF noise reports, a custom alert level, saved reference sounds and a Live Activity, for $24.99 a year with a 3-day free trial, $3.99 a week, or $34.99 once. There is no account, and sound is only saved when you start a recording and stays on your iPhone.

Loudmark is not a certified Class 1 or Class 2 sound level meter. It is built for everyday checks and personal records, not formal measurements.