# 100 Days Of ML Code — Day 077

Jehoshaphat I. Abu
·Oct 1, 2018·

## Recap From Day 076

Day 076, we looked at the first property of sound waves. You can catch up using the link below. 100 Days Of ML Code — Day 076 Recap From Day 075medium.com

Today, we will continue from where we left off in day 076.

## Frequency

“Frequency is the speed of the vibration, and this determines the pitch of the sound. It is only useful or meaningful for musical sounds, where there is a strongly regular waveform.”

Frequency is another really important property of waves. If we look at the sine wave below there’s a couple of important terms to think of. The very top point of the sine wave is called its peak. And the very bottom point after the peak as seen below is called its trough. And so, if we measure the distance from one peak to the next peak, that is called Cycle. The wavelength is the distance from crest to crest, trough to trough, or from a point on one wave cycle to the corresponding point on the next adjacent wave cycle.

Frequency is simply measured as the number of cycles per second. And is measured in a unit called Hertz, which is usually abbreviated as Hz so for instance in the video below is a sine wave at 440 Hz. The note A which is above Middle C has a frequency of 440 Hz. It is often used as a reference frequency for tuning musical instruments.

So, what frequencies can we as human beings actually hear? What you usually see people say is that from about 20 Hz up to about 20,000 Hz. It’s important that you understand this is all approximate. And I want to delve into that in a little more depth to explain exactly what I mean.

First of all, when we’re at the low end of a spectrum when we get below 20 hertz, we might very well still hear the sounds. But that’s when it stops sounding like a pitch to us, and starts sounding more like rhythm. So as an example, if I play you something at 10 Hz e.g a saw tooth wave. What you’ll hear is that it is not going to sound anymore like a pitch but it’s going to sound like rhythm.

So you can hear ten times a second something going duh duh duh duh duh and so on. so, that’s what happens in the low end of the spectrum. On the high end, the 20,000 Hz end different people may be able to hear up to different levels. Particularly as we get older we have a harder and harder time hearing those really high frequencies.

One final note here is that some animals have different ranges of hearing than we as humans do. dogs, for instance, can hear as high as 40,000 or sometimes even 60,000 Hz. So that’s why when you see a dog whistle, it’s just making a tone that’s higher than 20,000 Hz, but falls well within the range of dog hearing.

That’s all for day 077. I hope you found this informative. Thank you for taking time out of your schedule and allowing me to be your guide on this journey. And until next time, be legendary.