100 Days Of ML Code — Day 083

Jehoshaphat I. Abu
·Oct 7, 2018·

100 Days Of ML Code — Day 083

Recap From Day 082

Day 082, we looked at Harmonic Series. You can catch up using the link below. 100 Days Of ML Code — Day 082 Recap From Day 081medium.com

Today, we will continue from where we left off in day 082

Fletcher-Munson Loudness Curves.

Let’s look at one more thing before we leave our discussion of psychophysics for now. I want you to play the chirp sound below. I want you to focus on how loud it sounds over the course of the chirp from 20 Hertz to 20,000 Hertz.

Does it sound like its ever getting louder or softer or does it feel like the loudness is the same the whole time? Okay, so the loudness is obviously changing as that goes from 20 Hertz up to 20,000 Hertz. The amplitude of that sine wave in the file is actually not changing at all. It’s using the full negative one to positive one range throughout but our perception of that is changing based on the frequency of the sin wave.

This is explained by this phenomenon called the Fletcher-Munson Loudness Curves.

What Fletcher-Munson Loudness Curves shows is that on our y-axis we have decibels, on our x-axis we have frequency. If we follow one of the contours above, if we’re changing our loudness as we go up we actually perceive that curve as being the exact same loudness throughout.

So in order to get something that sounds like it’s equally loud from 20 Hertz all the way up to 20,000 Hertz we actually have to change it’s amplitude, in order to kind of fake our ears into hearing it sound like it’s the same. Because our ears are more sensitive, to a broader range of dynamics, especially around 3 to 5,000 Hertz.

Then let’s say at the very low end of the spectrum or even at the very high end. So this is another example about how frequency and loudness come together in our brains as we’re hearing sounds to create effects that are very different from what we might see if we’re just looking at a waveform.

So to review what we’ve covered in the past three days, we talked about psychoacoustics as describing how we perceive sound and not just how it exists acoustically in the world or how we might represent it as a waveform. We particularly talked about loudness versus amplitude, and we talked about pitch versus frequency. We looked at the Fletcher-Munson Loudness Curves as a really good example of this.

That’s all for day 083. 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.