The Period of a 440 Hz Sound Wave is

2.1 Pitch, Frequency, Menses, Loudness, Timbre

To brainstorm our discussion, we will consider the attributes or characteristics of any kind of moving ridge. Each of these characteristics can be associated with something that we hear in a sound wave.

The most noticeable attribute of a wave is that information technology repeats in time. Whether information technology is a vibrating cord on a violin or waves breaking at the shore, something is repeating. Each repetition is called an oscillation:

An oscillation
is one segment of a repetitive motion.

Pitch, Frequency, Period

Musical notes or tones take a
pitch. The pitch of a particular note is often given as a number. For example, the note “A” in the eye of a pianoforte is designated A=440. Now, the question is 440 what? This number is how many oscillations occur in 1 second.

If you lot pluck a violin cord tuned to Heart A, the cord will vibrate or oscillate back and forth and will have a sure pitch. The technical term for
pitch
is
frequency
and the frequency referred to here is
how many times in one second the string oscillates dorsum and forth:

Pitch of Middle A corresponds to a frequency of 440 oscillations in 1 second.

Physicists practice not like to keep write expressions out like this all of the time, so a autograph has been adult. We can write,

A 440 = 440 oscillations per second = 440 oscillations/second = 440/sec = 440 Hz.

Each way of writing this gets progressively more compact. Since frequency ever refers to some number of oscillations, we practise not have to keep writing “oscillations”. Also, “per second” is more easily written as /2d, and second is abbreviated as sec. What may be more unfamiliar is the designation that “/sec” = “Hz”. Hz is an abbreviation of the unit of measurement Hertz, named after the physicists Heinrich Hertz. 1 Hertz corresponds to 1 oscillation/2d.

Once we empathise the pregnant of a pitch or frequency of 440 Hz, we can ask a related question: how long does ane oscillation of the vibrating string take? If the string oscillates 440 times in 1 second, then each oscillation will have (1/440) seconds. Another style to look at this is the following: if each oscillation takes (ane/440) seconds then 440 oscillations will take one second. This is the aforementioned as proverb that at that place are 440 oscillations/second.

And so, the fourth dimension it takes for ane oscillation is chosen the
catamenia, and the period is related to the frequency by:

Period = 1/frequency

For the case of a pitch of 440 Hz, the period will exist:

1/(440/sec) = (1/440) sec = 0.00227 sec

= ii.27 millisecond

= 2.27 msec.

Again, we have used some shorthand notation. If the period is rather small, nosotros don’t want to go on writing lots of zeros after the decimal point, and so we utilize scientific notation, instead. ten^-iii seconds corresponds to 1 millisecond and 1 millisecond is abbreviated as 1 msec. This is particularly convenient for sound waves, as the periods of audio waves are generally around 1 to 100 msec.

EXAMPLES

one. Consider the Globe going around the sun. Is this motion repetitive? What would an oscillation represent to? What is the menstruum and frequency of the motion?

two. What is the period and frequency of the wave on the following graph?

Repetitive sounds can be formed in unlike ways. The nearly common, of class, is from a musical instrument. But, now, consider the situation where you are standing in front of a set of bleachers and you lot strike a bass drum:

The individual echoes of the pulsate off each step are delayed from one another. So, to the drummer the echoes form a repetitive sound which then is heard as a pitch. Anyone who has played in a marching band can attest to this!

Amplitude – Loudness

Besides the pitch of a musical notation, perhaps the nigh noticeable feature in how loud the note is. The
loudness
of a sound moving ridge is determined from its
amplitude. While loudness is only associated with sound waves, all types of waves have an aamplitude. Waves on a calm bounding main may be less than 1 pes high. Expert surfing waves might be 10 feet or more in amplitude. During a storm the amplitude might increase to 40 or l feet.

Many things can influence the amplitude.

1. What is producing the sound?
2. How far are you from the source of the sound? The further away the smaller the amplitude.
3. Intervening material. Audio does not travel through walls as well as air.
4. Depends on what is detecting the wave audio. Ear vs. microphone.

Shape of the repetitive motion.

Although a wave repeats in time, its movement during on oscillation can be simple or highly complex. For example, the post-obit two graphs each prove repetitive motility and the period and frequency of the motion is the aforementioned in both cases.

In fact, their amplitudes are also the same. Thus, if these two waves represented audio waves, the pitch and loudness would exist the aforementioned in both cases. But would they sound
exactly
the same? The answer is No, because there is one more than attribute to sound waves that y’all are familiar with, and that is
tone quality. This is what makes different instruments sound unlike. A violin and a trumpet can play the same pitch with the same loudness, but we tin can easily tell them apart, because they have a different tone quality. In fact, the same instrument can create different tone qualities. If y’all pluck a guitar in different ways, yous can go quite dissimilar tones. Endeavor information technology! The technical musical term for this is
timbre. For general waves, we refer to the
shape
of the moving ridge or sometimes the
waveform.

In the first lab, you will experiment with all three characteristics of sound waves: frequency, dependence of loudness on altitude from the sound source, and timbre.