FootprintID and Mapping Frequencies in Matlab from Audio Files

In one of my other courses (Foundations of Intelligent Infrastructure), we went through an exercise today where we recorded sound and then used Matlab to map frequencies.

My group measured the sound of different shoes stomping on the concrete hall in Porter. Graphs showing frequency and sound below.

Our experiment reminded the professor of a project at CMU where floor sensors are used to measure movement across spaces. The specific application discussed is in elder care, but also may be a way to provide less invasive monitoring of spaces.


Matlab code (note: need to drop sound file into the same folder as the Matlab file):

clear all; clc;

% Load signal in the time domain, x (fs is the sample rate in hertz)
[x,fs] = audioread('takeone.m4a');
tb = (0:1/fs:(length(x)-1)/fs); % Convert samples, k, to time base, t
xlabel('Time (seconds)')

% Play the sound

% Use the fft command to compute the DFT of the signal. 
m = length(x);         % Window length, N
y = fft(x,m);          % DFT of signal
f = (0:m-1)*(fs/m);    % Frequency range
p = y.*conj(y)/m;      % Power of the DFT

% Plot up to the Nyquist frequency:
xlabel('Frequency (Hz)')
title('Five Shoe Stomps on Concrete Floor')
grid on;
xlim([0 1000])        % Zoom in on relevant range



Gestures to control Holograms (within limits)

We talked about how tiring gestural interfaces can be in class. I came across this project – the Holographic Theater- by Simmetrico while looking for some interactive design examples. I think it’s interesting that they choose to limit the gestures to a ‘portal’ area- maybe this kind of ‘area limit’ could support a type of ergonomics for gestural interfaces:




Piano Visualizer: Combining Sound and Visualization

These have become popular on my Youtube suggestions list:

There are multiple resources for piano visualization. They can be mesmerizing to watch. They are also used for interactive, remote piano instruction. When I started playing piano again after about 15 years, I found that videos were more helpful than sheet music (which I had to re-remember how to read).

Beats Headphones Noises – James Kyle

When pairing and unpairing my headphones, I noticed that it plays a little jingle that ends on a high note when paired and a low note when unpaired. It seems natural at this point that a higher note at the end would indicate a connection because I have been using them for so long but it makes me wonder if that would have always been the case. I don’t know much about music and chord progressions but I would think that a higher note ending would convey happiness consistent with how the manufacturer wants you to feel when you use their products, and a lower note ending would convey sadness or some type of negative motion for stopping use of their product.


On the topic of pairing noises, I noticed the sound another speaker makes when in paring mode resembles a radar blip which is a cool experience to give the user. I think the sound adds a layer to the experience of pairing a device by tying it to searching for non-visible objects.

Error Sounds – MATLAB’s Assortment of Error Noises

When running a MATLAB script, there are a few things that trigger a sound to go off. The first of these is when a break in the code is set for debugging which for a while triggered a nice sounding double beat almost like a wooden percussion instrument. The second is when an error happens in the code and it stops running as a result invoking the same noise. While the first use case is very informative, the second case is not so. Recently, my perspective on these sounds changed as I listened to another friends computer make a screaming sound as the program encounters an error. This slight change in the error noise changed my whole perspective on what was happening in the script.

Ambient Sounds: Washing Machines and Credit Card Machines

Growing up, the washing machines I knew would indicated that clothes were ready to put into the dryer either by 1) silence, or 2) a long, flat buzzing noise. Newer washing machine models have a new approach (so distinct I remember my mother commenting on her new one from several years ago)- now, they sing. The latest one in my current unit has lets loose a rousing, merry tune for about 30 seconds before falling quiet. It’s catchy, and it feels more like a cheerful reminder than an angry “get-over-here-and-finish-your-chores-now” admonishment.

Another (relatively) recent tone change is the sound of the card machine at cashier registers. Older card machines would make more unpleasant noises (buzzes, beeps) that carried a vaguely disapproving connotation, while newer ones make a cheerier sound. It makes sense that a vendor would want the card machine to make a gratifying noise, since it rewards the customer. It wasn’t something I ever thought of before the happier noise was more prevalent. After that, it seemed a no-brainer that when completing a credit card transaction, happy noises should be coming from the machine that takes my money. Although I realize it is all my human auditory perception, the older, angrier-sounding machines begin to feel undeserving.

The Secret Life of Components (Connectors) – James Kyle

When I first saw this video, I was shocked that there was 45 minutes worth of content just on different ways to connect wires. I kind of agree with a lot of his thoughts on the usefulness of the different types of connectors, specifically the “chocolate bar” connector. It just seems very bulky and hard to use compared to other connectors like the ones with “springy bits”. In my experience, screw terminals don’t hold wires very well so my favorite connector by far was the one where you stick the screw driver in but the wire in and then take the screw driver out and the springy bit clamps onto the wire. I thought the waterproof clamp was cool too given how easy it looks to connect for the protection it provides.

Photocopier How It Works

Watching the video I had a rough idea of how copiers worked in the modern era with sensors that sense the image and convert it into a file which it can then print multiple times. This was completely different to how photocopiers actually ran in the past which was very interesting to me. The way that one would photocopy something in the past would use a fine layer of powder deposited onto the piece of paper through a series of electrode wires and rollers. The paper would then run past a heater which would melt the toner onto the paper resulting in the final product. While watching him describe this process, the fact that papers came out warm from printers made so much more sense. The complex mechanical processes behind these printers was also very interesting to look at and learn about. I never realized how mechanically intensive the printing process used to be up until very recently. Finally, I thought the process of using electrons to transfer the negative an image was very interesting because it made for some movie magic like videos. For instance, when he would transfer the image onto the selenium, there would be nothing visible until he poured the powder on top and only where the charge remained would the powder stick. I thought this process was very cool.

Motion-Sensor(?) Split Flap

I was staying at this hotel for work and I was convinced this was a motion-sensor split flap, since it never seemed to turn on until I rounded the corner into the elevator bank. The flaps make a very satisfying noise- a homage to the train station boards.  There is a link to a video that I took below. According to the article posted below, it’s on a timer, not a motion sensor, but at the time, I thought it was a cool use of a motion sensor.


The Ritz-Carlton