Unit 28 · Sound, Rhythm and Recorded Music

Put two fingers on the front of your throat and hum. You can feel a buzz. Now stop humming. The buzz stops too. That buzz is a vibration: a quick back-and-forth movement. Your vocal folds, two small flaps inside your throat, are shaking many times each second.

Every sound you have ever heard started this way. A drum skin shakes after the stick hits it. A guitar string shakes after it is plucked. A speaker has a cone that pushes out and pulls in. Even a clap makes your hands and the air between them shake for a moment.

Sometimes the shaking is too fast or too small to see. You can still find it. Sprinkle a little rice on a drum and tap the drum. The rice jumps. Put your hand on a speaker playing music. You feel it tremble. When the shaking stops, the sound stops. A sound source is anything that vibrates and starts a sound.

When a speaker cone pushes out, it squeezes the air right in front of it. That squeezed air pushes on the air next to it. Then that air pushes the next air. The push passes along like a line of people bumping shoulders. This traveling push is a sound wave.

Here is the surprising part. The air near the speaker does not fly to your ear. Each bit of air moves forward a tiny bit, then springs back. What travels is the pattern of pushes, and the energy it carries. At the block party, no wind came from the speaker. Energy came.

A sound wave has places where air is squeezed together and places where it is spread apart. Scientists call the squeezed places compressions. The spread-out places are called rarefactions. A speaker making a steady note sends out compression, spread, compression, spread, over and over, as long as it keeps vibrating.

If sound is a chain of pushes, it needs something to push. The material a wave travels through is called its medium. For the block party, the medium was air. But sound also travels through water and through solids like wood, metal and the ground.

In the 1600s, scientists built pumps that could pull most of the air out of a glass jar. Robert Boyle, working in England, put a ticking watch inside such a jar. As he pumped the air out, the ticking grew fainter. When he let air back in, the sound returned. With less medium, less sound got out.

Outer space is almost a perfect vacuum, a space with nearly no particles at all. So astronauts cannot talk to each other through empty space the way we talk in a room. They use radios. A radio sends light-like waves, which do not need a medium, and the receiver turns them back into sound inside the helmet.

Pluck a thick, loose guitar string and you hear a low note. Pluck a thin, tight one and you hear a high note. The difference is speed. The thin string vibrates back and forth many more times each second. How high or low a sound seems is its pitch.

Scientists count vibrations per second. That count is the frequency. It is measured in hertz, written Hz. One hertz means one vibration each second. The A note that orchestras tune to is 440 Hz. The string making it moves back and forth 440 times in one second.

Double the frequency and you get the same note, only higher. Musicians call that jump an octave. The A above 440 Hz is 880 Hz. The A below is 220 Hz. On a drum machine, a deep kick drum is mostly low frequencies, and a tiny hi-hat is mostly very high ones.

Tap a drum softly, then hit it hard. The pitch stays about the same, but the hard hit is louder. When you hit harder, the drum skin moves farther from its resting place. It squeezes the air more. The size of the vibration is its amplitude.

Loudness is how strong a sound seems. More amplitude means more energy in the wave, and it seems louder. Loudness is often measured in decibels, written dB. The scale is not a simple count. Every 10 dB step means the sound carries about ten times more energy.

So pitch and loudness are two different things. Pitch comes from how fast something vibrates. Loudness comes from how big the vibration is. A soft high note and a loud high note have the same frequency. On the oscilloscope, a louder sound draws taller waves. A higher sound draws waves packed closer together.

Sound is fast, but not instant. In air at room temperature it travels about 343 meters each second. That is why you see lightning before you hear thunder. The light arrives almost at once. The sound takes about three seconds to cover each kilometer.

Sound moves even faster through water and faster still through steel. In solids and liquids the particles are packed close, so they pass each push along quickly. Put your ear on a long metal railing while a friend taps the far end. You may hear the tap through the metal first, then through the air.

The distance from one compression to the next is the wavelength. You can find it with a simple rule: wavelength equals speed divided by frequency. A 440 Hz note in air has a wavelength of about 343 divided by 440, or about 0.78 meters. Low bass notes have long waves, several meters long. That is part of why they carry around corners and through walls.

Your outer ear is shaped like a funnel. It gathers sound waves and sends them down a short tube to the eardrum, a thin skin stretched tight. When a sound wave arrives, the eardrum vibrates in the same pattern as the wave.

Behind the eardrum sit three tiny bones, the smallest in your body. They pass the vibration along and make it stronger. The last bone presses on the cochlea, a snail-shaped tube filled with fluid. Inside the cochlea are thousands of tiny hair cells. Different hair cells respond to different pitches.

When the hair cells bend, they send signals along a nerve to the brain. The brain does the rest. It tells a voice from a drum, finds the beat, and notices your name in a noisy room. Brains differ. Some people notice small sounds that others miss. Some people hear best with a quiet room or with headphones. Knowing what helps your own ears is useful science.

Your ears do not hear every vibration. A young person with typical hearing hears from about 20 Hz, a very deep rumble, up to about 20,000 Hz, a thin whine. This span is your hearing range. As people get older, the top of the range usually drops.

Sounds too high for us are called ultrasound. Dogs can hear some of them, which is how a dog whistle works. Bats send out ultrasound and listen for echoes to find insects in the dark. Doctors use ultrasound to make pictures of the inside of the body.

Sounds too low for us are called infrasound. Elephants can use very low rumbles to stay in touch across long distances. Very low bass, near the bottom of our range, is often felt in the chest as much as it is heard. That is the thump you felt at the block party.

Hair cells in the cochlea are delicate. A very loud sound, or a loud sound that goes on for hours, can bend and break them. Once they are gone, the body does not grow new ones. This is called noise-induced hearing loss. It can happen without any pain.

The U.S. government’s safety scientists say sound at 85 dB, about as loud as heavy city traffic, is safe for up to about eight hours a day. Each 3 dB louder cuts the safe time in half. At 100 dB, a level some headphones and concerts reach, the safe time is only about 15 minutes.

Protecting your hearing is simple. Turn it down. Take breaks. Step back from the speakers. Wear earplugs or ear defenders at loud events. Some people’s ears are extra sensitive to noise, and ear defenders help them stay comfortable. That is a smart tool, just like sunglasses on a bright day.

A microphone works like an ear. Its thin plate vibrates with the sound, and it turns those vibrations into a changing electrical signal. An oscilloscope draws that signal as a line moving across a screen. Time runs from left to right. Up and down shows the push and pull of the air.

Now you can read a sound like a graph. Taller waves mean bigger amplitude, so a louder sound. Waves packed closer together mean higher frequency, so a higher pitch. The time for one full wave is the period. A 440 Hz note has a period of about 2.3 thousandths of a second.

Different sources draw different shapes. A flute draws a smooth, rounded wave. A buzzy synthesizer might draw a sawtooth. A hi-hat draws a fuzzy scribble, because it mixes many high frequencies at once. The shape of a wave is part of why a trumpet and a violin sound different, even when they play the same note.

Listen to a clock. Tick, tick, tick. Each tick is an event, and the time between ticks is always the same. When something repeats at an even spacing, it has a beat. The steady feeling underneath the beat is called the pulse.

Your body is full of beats. Your heart beats. You breathe in and out. When you walk, your feet land left, right, left, right at a fairly even pace. Music takes this idea and makes it something to share. Everyone can feel the same pulse and move with it.

A beat is a lot like a wave. Both repeat. A wave repeats in space and time, and a beat repeats in time. The time from one beat to the next is the beat’s period, the same idea you met with sound waves. A slow song has a long period between beats. A fast song has a short one.

How fast is the beat? Musicians call the speed of the beat the tempo. They measure it by counting how many beats fit in one minute. That unit is beats per minute, or BPM. A clock that ticks once a second is at 60 BPM.

BPM makes the math simple. At 60 BPM, each beat lasts one second. At 120 BPM, twice as many beats fit in the minute, so each beat lasts half a second. You can always find the time for one beat: divide 60 seconds by the BPM.

Different kinds of music tend to use different tempos. Slow songs might sit near 70 BPM. Many hip hop tracks sit roughly between 85 and 100 BPM. House music is often around 120 to 130 BPM. The Drum Machine has a tempo control, so you can hear the same pattern slow and fast.

You do not need a machine to find a tempo. You need a clock and your ears. Start a timer, tap along with the beat, and count taps for 15 seconds. Multiply by 4, because a minute holds four sets of 15 seconds. That is your estimate of the BPM.

Any single count can be a little off. You might start tapping late or lose one beat. Scientists handle this by repeating a measurement and comparing. Count three times. If you get 29, 30 and 30 in 15 seconds, the tempo is about 120 BPM. The results agree, so you can trust them more.

You can measure other rhythms the same way. Find your pulse on your wrist and count for 15 seconds. Count a friend’s steps as they walk. Count the chirps of a cricket on a summer night. Every repeating event has a tempo you can measure.

Beats are easier to follow in groups. Musicians gather them into bars, also called measures. In most pop, hip hop and house music, each bar has four beats. You count them: one, two, three, four, one, two, three, four.

The first beat of each bar, the one, often feels strongest. It is where a new idea tends to start. The pattern of how many beats are in each bar is the time signature. Four beats per bar is written 4/4, and it is so common that people call it common time.

Not all music counts in four. A waltz counts in three: one, two, three. Some music from the Balkans and from India uses longer, uneven groups. Counting is a tool. Once you can count the bars, you can tell where you are in a song, just like a map tells you where you are on a street.

A drum machine has a row of 16 buttons. Each one is a step. Together they make one bar. Since the bar has four beats, each beat gets four steps. Steps 1, 5, 9 and 13 land right on the four beats. The steps in between fall on the quick counts you can say as one-e-and-a, two-e-and-a.

Turn a step on, and the drum plays at that moment. Turn it off, and that moment is silent. The machine moves through the steps in order, then loops back to step 1. This loop is a sequencer: a tool that plays events in a set order, again and again, perfectly on time.

The steps are equal slices of time. At 120 BPM, one beat lasts 0.5 seconds, so each step lasts 0.5 divided by 4, which is 0.125 seconds. The whole bar of 16 steps lasts 2 seconds. Change the tempo and every step stretches or shrinks together, so the pattern keeps its shape.

Listen closely to most beats and you will hear three main parts. The kick drum is the low thump. The snare is the sharp crack. The hi-hat is the quick tick or tss. Each one has a job, like players on a team.

A classic pattern goes like this. The kick plays on steps 1 and 9, the one and three. The snare plays on steps 5 and 13, the two and four. The hi-hat plays on every odd step, 1, 3, 5 and so on, eight times per bar. Say it out loud: boom, tss, crack, tss, boom, tss, crack, tss.

House music often puts the kick on all four beats, steps 1, 5, 9 and 13. People call that four on the floor. Hip hop often moves the kick around between the beats, which gives it a bounce. Small changes in where the drums land change how a beat feels in your body.

Play a hi-hat on all 16 steps and you get tick-tick-tick-tick, perfectly even. It can sound stiff, like a robot. Now nudge every second tick a little later. The first tick in each pair gets longer, the second gets shorter. The rhythm starts to lope. That is swing.

Jazz musicians have swung for more than a hundred years. Early drum machines added a swing setting to copy that human feel. The machine measures swing as a percentage. At 50 percent the steps are even. At about 66 percent, the first step of each pair takes up about two thirds of the pair, and the groove bounces hard.

Swing shows something important about rhythm. The groove, the feel that makes you move, can come from tiny shifts in time, less than a tenth of a second. Your brain notices these shifts even when you cannot name them. Try the swing button on the Drum Machine and listen to the same pattern change its whole mood.

Put on a song and watch a room. Heads nod, feet tap, and often nobody decided to do it. Moving in time with a beat is called synchronizing. People do it from a young age, and it gets stronger with practice. Rowers pull together. Marchers step together. Dancers at the Warehouse moved together.

Scientists who study the brain find that hearing a steady beat activates areas that plan movement, even when you sit still. The brain starts to predict when the next beat will come. When it guesses right, that can feel satisfying. That may be part of why a steady pulse feels good.

A steady pulse can also be a tool. Some people focus better with a quiet, steady beat in their headphones. Some people rock, tap or bounce a knee to think. That movement is the body finding its own rhythm, and it can help. Therapists use rhythm to help people walk more evenly after an injury and to practice speech. A beat is something the body understands.

Beats are not only made by people. Crickets chirp in rhythm. Frogs call in turns. Fireflies in some places flash together. Your heart keeps its own tempo, faster when you run, slower when you rest. These are natural rhythms.

In 1897, a physics teacher named Amos Dolbear wrote about crickets. He noticed that crickets chirp faster when the air is warmer and slower when it is cooler. A cricket’s body warms and cools with the air, so its muscles work faster in the heat. Dolbear turned the chirp rate into a way to estimate temperature.

Scientists still use this idea. The chirp tempo is a variable that changes along with another variable, temperature. When two things change together in a steady way, you can use one to predict the other. You will do the same with your own beats in Chapter 64.

Here is a strange fact that joins this chapter to the last one. Take a single click and repeat it 4 times a second. You hear a fast rhythm. Repeat it 10 times a second and it becomes a buzz of clicks. Repeat it more than about 20 times a second, and your brain stops hearing separate clicks. You hear a low tone.

Why? A click repeated 100 times a second is a vibration at 100 Hz. That is a frequency, and frequency is pitch. The difference between a rhythm and a note is only speed. Rhythm lives at slow repetition rates. Pitch lives at fast ones. The threshold between them sits around 20 per second.

So a beat at 120 BPM is a very slow vibration, 2 per second. A bass note at 110 Hz is the same idea sped up 55 times. Musicians and scientists both work with repeating patterns in time. They just work at different speeds.

Twenty years before Edison, a French printer named Édouard-Léon Scott de Martinville built the phonautograph. Sound shook a thin skin, and a bristle attached to it traced a wavy line on paper blackened with soot. It could write sound down, but it could not play it back.

Edison’s phonograph of 1877 could do both. The needle pressed the wave into tinfoil. Running the needle back over the track made it shake the same way again. The shaking plate pushed the air, and the sound came back out. For the first time, a recording could be heard.

In 2008, researchers scanned some of Scott’s old paper tracings and used computers to turn the lines back into sound. One of them, from 1860, is a person singing a few notes of the French song Au clair de la lune. It is one of the oldest recordings of a human voice we can hear today.

Look at a vinyl record in bright light. You see fine rings. It is actually one very long groove that spirals from the outside edge toward the center. Under a microscope, the groove is not smooth. Its walls wiggle from side to side.

Those wiggles are the sound wave, frozen in plastic. A slow, wide wiggle is a low, loud note. A quick, tiny wiggle is a high, soft note. When the record spins, a tiny tip called the stylus rides in the groove. The wiggles push it back and forth, the same way the air pushed the microphone.

The stylus is joined to a cartridge, which turns its movement into a small electrical signal. An amplifier makes the signal stronger, and a speaker cone moves with it, pushing the air. The wiggle in the plastic has become a wave in the air again. A stereo record even carries two signals, one on each wall of the groove, for the left and right speakers.

Records are made to spin at a set speed, counted in revolutions per minute, or rpm. Long-playing albums spin at 33 and one third rpm. Seven-inch singles often spin at 45 rpm. Old shellac records from before about 1950 spin near 78 rpm.

Play a record at the wrong speed and something odd happens. Play a 33 record at 45, and the voices sound high and chipmunky, and the song rushes. Play a 45 at 33, and the voices drop low and slow. The wiggles pass the stylus faster or slower, so every frequency and the whole tempo change together.

The math is neat. 45 divided by 33 and one third is 1.35. Every frequency goes up by 35 percent, and the BPM goes up by the same amount. A 100 BPM song becomes a 135 BPM song. On the Turntables you can switch speeds and hear this for yourself.

In the mid-1970s in the Bronx, in New York City, DJs were inventing hip hop at block parties. One teenager, Grand Wizzard Theodore, is often credited with making scratching into a technique. He stopped a spinning record with his hand, moved it back and forth under the needle, and liked the sound.

Here is the science. When your hand pushes the record forward, the stylus reads the groove forward, and you hear the sound. Pull it back and the stylus reads the groove backward, so the sound plays in reverse. How fast you move your hand sets the playback speed, and that sets the pitch. A fast push gives a high zip. A slow drag gives a low growl.

A scratch is really a performance of physics. Your hand becomes the motor. You are choosing, moment by moment, how fast and in which direction the recording plays. DJs combine this with a crossfader, a slider that cuts the sound in and out, to make rhythms on top of the beat.

Most DJ turntables have a slider called a pitch control. It speeds the platter up or slows it down by a few percent. On many classic turntables, the range is about 8 percent up or down. A record at 120 BPM can be nudged to about 110 or about 130.

Because a record plays pitch and tempo together, speeding it up raises its pitch slightly too. Over a small range, most listeners barely notice. Over a big range, voices start to sound strange. Many digital tools today can change tempo without changing pitch. A turntable cannot. Its sound is tied to its speed.

Why would a DJ want to change the speed at all? Two songs are rarely the same tempo. To blend them smoothly, the DJ has to make them match. That is the next lesson. The pitch slider is the tool, and your ears are the measuring instrument.

When a DJ blends two records, both play at once for a while. If their beats do not line up, the kicks clatter like two people walking out of step. Lining them up is called beatmatching. It needs two things: the same tempo, and beats that land at the same moment.

First the DJ matches tempo with the pitch control, listening in headphones to the new record while the old one plays for the crowd. Then the DJ lines up the downbeat, the first beat of a bar, often by giving the new record a small push or drag by hand. If the beats slowly drift apart, the tempos are still a little off.

This is a real measurement task, done by ear. The DJ compares two rhythms, notices drift, adjusts one variable, and checks again. Scientists do the same when they calibrate an instrument. The Turntables let you try it with two decks and a crossfader.

A record stores sound as a continuous wiggle. A computer cannot store a wiggle. It stores numbers. So digital recording measures the height of the sound wave again and again, very quickly. Each measurement is a sample. The list of samples is the recording.

How often you measure is the sample rate, counted in samples per second, or hertz. A music CD takes 44,100 samples every second. That sounds like a lot, and it is. Measuring often matters because a wave that wiggles fast needs many measurements to catch its shape.

There is a rule for this. To record a frequency, you must sample more than twice as fast as that frequency. So a sample rate of 44,100 Hz can capture sounds up to about 22,000 Hz, just above the top of human hearing. That is why the CD rate was chosen. A slower sample rate loses the highest sounds.

Each sample is a measurement of height. But how exact is it? Imagine measuring with a ruler marked only in whole inches, versus one marked in tiny millimeters. The finer ruler gives more exact answers. In digital sound, the fineness of the ruler is the bit depth.

A bit is a single 0 or 1. With more bits, you can write more different numbers. Each extra bit doubles the count. 8 bits can store 256 different heights. 12 bits can store 4,096. 16 bits, used on CDs, can store 65,536.

When the ruler is rough, each sample gets rounded to the nearest mark. That rounding adds a faint hiss or grit to the sound, called quantization noise. More bits means smaller rounding and a cleaner sound. Fewer bits means a rougher, crunchier sound, which some musicians love on purpose.

In 1987, a sampling drum machine came out that would become a legend. It could record short sounds, like a drum hit from an old record, and play them back on its pads in a sequence. Its sample rate was 26,040 samples per second. Its bit depth was 12 bits.

Those numbers had limits. At 26,040 Hz, the highest sound it could store was about 13,000 Hz, so the sparkly top of the cymbals was cut off. At 12 bits, each sample had 4,096 levels, so there was a little grit. Producers also sped samples up to fit more into its short memory, then slowed them down on playback, which added even more crunch.

Hip hop producers in New York loved that sound. It made drums feel heavy, warm and a little rough. Many producers still add grit on purpose to copy it. The Drum Machine on this site copies that 1987 recipe, 12 bits at 26.04 kHz. A limit in a tool became a style. That happens a lot in the history of technology.

A record groove is an analog recording. Analog means the stored shape changes smoothly, just like the wave itself. A tape recording is analog too. Every tiny change in the wave becomes a tiny change in the groove or the tape.

A CD, a phone recording and a drum machine sample are digital. Digital means the wave is stored as a list of separate numbers. Between samples there is no information, but with enough samples and enough bits, your ear cannot tell the difference.

Each way has strengths. Digital copies are exact; copy a file a thousand times and it does not change. Analog records wear a little each time the stylus rides the groove, and dust adds pops. But a record can be scratched by hand, slowed by a finger and felt in a way a file cannot. Many DJs today use both: digital files controlled with special records that act like analog ones.

Engineers do not start by building. They start with a question: what is this for? Jada’s purpose was to help a class settle. Another student might want a beat for a dance, for a workout, or for walking the dog. The purpose shapes every choice.

Next come the criteria, the things the design must do to succeed. For a calm beat, the criteria might be: slow tempo, steady pulse, no sudden loud sounds. Then come the constraints, the limits you must work within. Maybe you have only 16 steps, one bar, and five minutes.

Writing these down first saves time later. When you are not sure whether to add a crash cymbal, check the criteria. No sudden loud sounds? Then leave it out. Criteria also tell you what to measure when you test. Design and science meet here: a clear goal leads to a fair test.

Most producers build a beat in layers. Start with the kick drum alone and get it feeling right. Then add the snare. Listen. Then add the hi-hat. Listen again. Each layer should earn its place.

Building in layers is like adding one ingredient at a time when you cook. If the soup tastes wrong, you know what changed. If you add everything at once and it sounds messy, it is hard to tell which part is the problem. This is also how scientists build a model: start simple, then add parts.

Leaving space is part of the design too. A step with no sound is called a rest. Rests give the beat room to breathe, and they make the sounds around them stand out. A beat with every step filled can feel crowded. For many people, a beat with space in it is easier to listen to and to move with.

Say your beat feels too rushed. You could change the tempo, move the snare, and turn off the hi-hat all at once. If it gets better, which change helped? You cannot tell. Change one thing at a time.

The thing you change on purpose is the independent variable. What you watch for is the dependent variable. Everything else you keep the same is a controlled variable. If you change the tempo from 90 to 80 BPM and ask three friends how calm it feels, tempo is independent, calmness is dependent, and the sounds and volume stay controlled.

This is the heart of a fair test. It works for beats, for plants, for medicine, for bridges. It is how Jada tested her beat: the same class, the same time of day, the same reading time, with and without the beat. Only one thing changed.

Play your beat into the Oscilloscope. The line jumps each time a drum hits and settles back between hits. The picture is the beat’s waveform. Reading it is like reading a graph: time runs left to right, and the height of the line shows the push and pull of the air.

Look for three things. First, how tall do the biggest waves get? That is the peak amplitude, the loudest moment. If the waves hit the top of the screen and flatten, the sound is clipping, too loud for the system, and it will sound harsh. Second, how quickly does each hit fade? That is its decay. Third, how far apart are the hits? That is the rhythm.

You can adjust the screen. Stretching the time scale lets you zoom in on one kick to see its individual wiggles. Squeezing it lets you see a whole bar. Changing the height scale lets you see quiet sounds. A good scientist chooses the scale that shows what they want to measure.

Play a kick drum alone into the Oscilloscope. You see a few big, rounded waves spaced far apart, and then they fade. Those far-apart waves mean a low frequency, often around 50 to 100 Hz for a deep kick. Big height means strong amplitude.

Now play the hi-hat alone. The line turns into a thin, jittery smear with no smooth shape. A hi-hat is made of many high frequencies at once, jumbled together. Scientists call a jumble of many frequencies noise, even when it sounds nice. The hi-hat also fades quickly, so its decay is short.

Put them together, and you can see why a beat works. The kick fills the low end with big, slow energy. The hi-hat fills the high end with fast, light ticks. They do not crowd each other, because they live in different frequency ranges. Mixing engineers call this giving each sound its own space.

Your drum machine says the tempo is 90 BPM. Is it? Scientists check. Play the beat into the Oscilloscope and measure the time from one kick to the next kick on the main beats. That is the beat’s period.

Turn the period back into tempo: BPM equals 60 divided by the period in seconds. If the kicks are 0.67 seconds apart, 60 divided by 0.67 is about 90. The measurement agrees with the setting. If you measure 0.60 seconds instead, the tempo is really 100 BPM, and something is set differently than you thought.

You can also check the steps. At 90 BPM, each of the 16 steps should last about 0.167 seconds. With swing on, the pairs of steps will not be equal; the first one will be longer. Measuring lets you see swing as numbers, not just a feeling. Record your measurements in a data table, with the setting in one column and the measured value in the next.

Making beats can mean hours in headphones. That is exactly when hearing damage can sneak up, because it does not hurt. Keep the volume at a comfortable level. A good check: if someone an arm’s length away has to shout for you to hear them, it is too loud.

Take listening breaks. Every hour or so, take off the headphones for a few minutes. Your ears get tired, and tired ears hear less detail. After a break, you will often notice things in your beat you missed. Producers call these fresh ears.

Everyone’s comfort level is different. Some people find certain sounds, like sharp hi-hats or sudden crashes, painful or overwhelming. That is useful information for a designer. It is fine to turn those sounds down, choose softer ones, or wear ear defenders. A beat that works for more people is a better design.

A sample can mean a single measurement, but in music it also means a piece of another recording used in a new song. Hip hop was built on samples: a drum break from a funk record, a horn line from a jazz record, looped and flipped into something new.

The sounds in those old records were made by real people: drummers, singers, engineers. Their work is protected by copyright, a law that gives creators rights over how their work is used. Professional musicians who sample a song usually ask permission and often pay the people who made it. This is called clearing a sample.

For school projects, you can use the sounds built into the Drum Machine, record your own sounds, or use sounds that are marked free to use. Either way, give credit: write down where each sound came from. Scientists do the same when they cite other people’s data. Credit is how we show respect for the work we build on.

You designed a beat. You measured it. Now share it the way scientists share their work: with a claim, evidence and reasoning. The claim is one sentence saying what your beat does. For example: my beat helps our class settle faster after lunch.

The evidence is what you measured. Jada’s class took an average of about 6 minutes to settle without the beat and about 4 minutes with it, over one week each. Her oscilloscope showed no clipping and a steady 70 BPM. Evidence is numbers and observations, not just feelings, though listeners’ comments count as evidence too if you collect them fairly.

The reasoning explains why the evidence supports the claim, using science. A steady pulse is easy for the brain to predict. A slow tempo is near a resting heart rate. No sudden loud sounds means nothing startles. Honest scientists also say what they are not sure of: one class, two weeks, and other things might have changed too.