Noise Crayon – Noise Amplitude to Light Spectrum Converter

Continuing on from my Ambient Noise Level Indicator, I wanted to create an enclosure and make it stand-alone – not requiring a computer to do the processing. I ended up with a little device that converts noise amplitude to the light spectrum: Noise Crayon.

The Ambient Noise Level Indicator used the MCU serial host Processing to perform a FFT and various averaging routines to create an indicator for ambient noise. The idea being that it would change colour when background levels rise above a threshold. Moving to an ATMEGA328, performing this processing – especially the FFT – is asking a little too much of it. There are libraries but I’ve heard of limited successes.

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SoundBar VU Meter Laminated Wooden Speaker

I felt that the battery powered Bluetooth speaker I made could be improved with more colour! Taking a leaf from the VU meters on amplifiers of the 80s, I decided it would be neat to sandwich clear acrylic between the plywood layers, each with an integrated LED that would form a full body amplitude meter.

Having a look around, I found a IC made by Texas instruments that did the VU meter job for me: the LM3915. Below is a photo series showing the construction and completed unit. I designed this version as a soundbar to sit below my monitors at work, so it doesn’t have a battery or Bluetooth, making the wiring easier inside and a slimmer unit. For this one I also used an Oak stain rather than a clear stain on the ply and filled the text with black acrylic, which looks much better I think.

Ambient Noise Level Indicator

As part of my work at MACH Acoustics – understanding how internal ambient noise levels affect different environments – I was inspired to create an indicator that shows when noise becomes higher than the base level. Some solutions already exist but they are pricey (because they used calibrated sound level meters), and not very engaging. I wanted something that could sit in a classroom and be a friendly indicator for the teachers and students, bringing the noise back down and perhaps learning something in the process!

The solution is a simple RGB led connected to the PWM outputs of an Arduino and uses Processing with the Minim Library to perform a FFT on the mic input – similar to a couple of other projects.

The operation is best described by the video below and commented code. I’ve added a handy GUI that allows the user to do a number of things:

  • View the mic reading, background sample, instantaneous sample, current colour and sample difference.
  • Change the threshold between colours and benchmark colour.
  • Set continuous sampling, direct LED/mic feedback
  • Resample the background
  • Set the frequency band that is used for the amplitude average – this is useful to demonstrate that it is working and also to ignore low frequency to only show speech for example; screechy children in a classroom!
The control panel when the Java applet is running.
The control panel when the Java applet is running.

Its only a prototype concept at the moment. I’d like to design an enclosure that would suit the particular environment, such as a glowing star or dragon for a classroom.

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MATLAB Finite Difference Time Domain Acoustic Modelling

As part of MACH Acoustics’ open window research, they wanted a FDTD model to visualise sound waves moving through various window opening scenarios. I created a FDTD function, that would create an impulse wave at a specified position then calculate discrete pressure points across a defined grid size and time step. Geometry (boundary conditions) could be loaded loaded into the function using scripts for different objects (opening, top/bottom swing window, baffle, etc), video saved and pressure, mic, time step data saved for repeat plotting (the solver took a few minutes to run so being able to plot existing data saved time). There is no currently no absorption so the sound does not decay, reflecting 100%. For short periods however this does not hinder the visualisation too drastically.

A GUI I created to control the simulation settings.
A GUI I created to control the simulation settings.

The videos below show it in action.

Opening with internal baffle plotted in isometric using surf

Opening with internal baffle plotted in isometric using surf