Hearing Matters: Decoding the Distinction Between Frequency and Loudness

When describing any sound, there are two characteristics that are more important than any others. These are frequency and amplitude, or in layman’s terms, pitch and loudness. However, there is a lot of confusion about these terms out there, particularly in regard to frequency. Let’s try and clear that up!

The Science of Frequency and Amplitude

Sound is really just the movement of air particles. A sound wave is a repeating pattern of moving particles, which travels through the air until it reaches your ears and you perceive it. (This is hard to picture, but just know that the particles aren’t shooting through the air toward you; it’s more like each particle wiggles back and forth temporarily, setting the particle next to it to wiggling, and so on, until the wiggle has transferred from one particle to the next to the next without any single particle actually going very far.) The particles can move faster, meaning more motions per second, or they can move in larger motions independent of how many of those motions occur each second. This is easier to understand in visual terms, so take a look at the following diagram:

If you look at the top two waves, you’ll see that the waveform on the right shows a lot more motions per second than the one on the left. This is frequency: how frequently (get it?) the air particles move. In other words, faster wiggles. The lower two waves have the same frequency – assuming the diagram shows one second, both waves are at three cycles per second, but the one on the left shows a much smaller motion than the one on the right. This is amplitude: not how fast the particles move, but how big the movements are.

You will perceive these patterns as pitch and loudness. More wiggles per second means higher frequency, which is perceived as higher pitch; fewer wiggles per second means lower frequency or pitch. If you’re unfamiliar with the term “pitch,” think of it as bass versus treble. Lower pitch is the bass, and higher pitch is treble. Think of a piano keyboard. The keys on the far left end of the keyboard are the lowest frequency, with the very lowest key being 27.5 cycles (wiggles) per second, and the very highest being 4186 cycles per second. Middle C is 261.6 cycles per second. That’s frequency. Now, you can play that Middle C very softly, or you can hit that Middle C just as hard as you can, and the second note will be a whole lot louder than the first – but it will still be 261.6 cycles per second no matter how loudly you play it. That’s amplitude.

Frequency is expressed in a unit called Hertz, or Hz. One Hz is equal to one cycle (or wiggle) per second. So that Middle C is at 261.6 Hz, meaning that when you play that key on the piano, you cause the air molecules to vibrate 261.6 times per second until the note dies away.

Amplitude is expressed in a unit called decibels, or dB. This is a little more complicated than Hertz, because it isn’t a linear scale, and furthermore, we use dB differently when talking about human hearing than when we talk about actual sound pressure level. Just know that more decibels means a louder sound!

Other ways to describe frequency and amplitude

Frequency is the same as:

  • Pitch
  • treble/bass
  • High, squeaky, piercing, shrill (treble)
  • Low, deep, rumbling (bass)

Amplitude is the same as:

  • Loudness (soft/quiet versus loud)
  • Volume
  • Intensity
Examples of high and low frequency sounds

High frequency sounds:

  • Birds chirping
  • Microwave or smoke alarm beeping
  • Mosquitoes buzzing
  • Mice squeaking

Low frequency sounds:

  • Thunder
  • Traffic/road noise
  • Fans
How frequency and loudness are related to human speech

Of course you already know that some people have higher pitched voices and some have lower. The pitch where you perceive someone’s voice is called the fundamental frequency; the average man has a fundamental frequency between 85-155 Hz, the average woman has a fundamental frequency between 165-255 Hz, and children average around 260-280 but decrease with age. Did you know, however, that regardless of fundamental frequency, every person’s voice produces sounds at a range of frequencies? Sounds that you use your voice to produce – think “ah,” “oh,” “ooh” – are the lowest frequency sounds in typical speech. Sounds that are just air – think “ss” and “ff” – are the highest pitched, as well as the softest. In between are sounds like “ch,” “g,” and “sh.” You can hear the difference pretty easily if you say “ss” out loud (yes, right now!) and then say “sh.” You’ll hear that the “sh” sound is lower pitched compared to the high-pitched hissing of the “ss.”

This article isn’t meant to be about hearing loss – we have plenty of those if you look around our website! – but an important thing to understand is that people don’t lose their sensitivity to all frequencies equally. The typical pattern of hearing loss which results from aging and noise exposure is this: a decreased ability to hear high frequencies, while retaining normal or near-normal low frequency hearing. This means you’ll lose the ability to hear some of those higher pitched sounds, but hear lower sounds as well as you always have, resulting in the perception of hearing but not understanding. Those higher sounds bring clarity to speech. So you may not feel like you need to hear birds chirping, smoke alarms beeping, or anything else that we listed previously as high-frequency sounds, but those high frequency speech sounds are mighty important if you want to understand what people are saying to you!

The third descriptor: Timbre

Frequency and amplitude – pitch and loudness – are the most important descriptors of sound, but they aren’t the only ones. The third main descriptor of sound is timbre, or sound quality, and while a full discussion of timbre is beyond the scope of this article, just know that almost all sounds contain many frequencies at once (called harmonics), all of them higher than the fundamental frequency which you perceive as pitch, and that the combination of all these tones in a sound is how you can identify whether you’re hearing a flute or a violin, or whether it’s your friend Sarah or your friend Mary on the phone when she says “Hi, it’s me!” Timbre encompasses all the ways you might describe a sound as rich and dark versus thin and reedy, nasally or gravelly, brassy or tinny or twangy or mellow. Interestingly, timbre is essentially a combination of the frequency and amplitude of those harmonics; it’s more complex than simply locating the pitch and loudness of a tone on a graph, but it’s still sound, meaning it still comes down to those wiggling air particles.