# What makes two sounds similar?

 P: 38 Hello, i have been wondering this for a long time... for example: if we say the word "hello" with a loud pitch scientifically speaking higher amplitude versus if we say the word "hello" with a low amplitude versus if we say "hello" really fast versus if we say "hello" very slow versus if we say "hello" normally the question: what make all the above sounds similar?? as in if we graph the above sounds what would remain constant in all the graph?? thank you
P: 5,632
Wikipedia has this to say:

 Propagation of sound The behavior of sound propagation is generally affected by three things: A relationship between density and pressure. This relationship, affected by temperature, determines the speed of sound within the medium. The propagation is also affected by the motion of the medium itself. For example, sound moving through wind. Independent of the motion of sound through the medium, if the medium is moving, the sound is further transported. The viscosity of the medium also affects the motion of sound waves. It determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible.
http://en.wikipedia.org/wiki/Sound_w...ansverse_waves

But the thing that REALLY makes them similar is that all sound is a longitudinal wave....
the above referenced articles discusses this....Light, in contrast, is transverse.
HW Helper
Thanks
P: 26,148
hello anj16!
 Quote by anj16 … if we graph the above sounds what would remain constant in all the graph??
the shape
it'll always be the same, except it may be higher or lower on the page, or stretched or squeezed horizontally and/or vertically

 PF Gold P: 1,909 What makes two sounds similar? anj16, Welcome to Physics Forums! It is important that we all use terms accepted by science to describe experiments. Otherwise, folks will be confused as to our meaning and miss the point. For example, the term "amplitude" is quite different from the term "pitch". As for your question in the OP, there are similiarities in those examples you gave. They are described by "acoustic signature". Just Google that and see the Wikipedia page plus references. In classifying and identifying particular ships and submarines and also in identifying specific species of birds and frogs we use an "acoustic fingerprint". Google that, too.
 P: 15,319 pitch (frequency) amplitude (loudness) tone/envelope (shape) harmonics (multiple sounds) For all your sounds, the first two can vary, but it is the third - the tone - that makes them all sound similar. Alternately, you could keep the pitch and amplitude the same and change the tone, to get sounds that are very different. Say the word 'woah' very slow, 'w' then 'o' then 'ah'. The major difference between the three is the tone of the sound. Tone is the shape of each individual peak/valley. There are sine waves, sawtooth, square waves etc. The wider the shape (within the cycle), the more round the tone (like 'o'). The thinner the shape, the thinner the sound (like 'w'). See here. There's a little audio clip on the right. There are other factors, such as harmonics, that play into the 'sound' of sound.
 Admin P: 23,723 If you wonder what makes them all be understood the same way - that is, why we hear "hello" each time, and not some other random word - check Liberman-Mattingly motor theory of speech perception (and related theories).
 P: 38 Thank you all for helping me out just to clarify DaveC426913 would i be consistent with your explanation if i say that the number of peak and valleys remain constant making the sounds sound similar???

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