1. Spectrogram basics
Here’s how to get a colourful representation of frequency over time using Audacity…
1 Most audio editors offer some means by which to analyse a sound. Let’s use the free Audacity audio editor to take a look at a complex sound made up of a few different timbres piled on top of each other. Open StackedTrack.wav in Audacity – we see the standard amplitude display.
2 Play the file and take a listen. A rattling prayer drum hits first, a set of chimes ring out for a bit, and a synthetic bass drone runs underneath. Most of the action is near the start, as our waveform shows. Go to the upperleft of the track and use the drop-down menu to select Spectrogram.
3 Now we can see more than just the overall amplitude of our waveform. The vertical axis represents frequency, while the colour depicts the amplitude of a given frequency: grey indicates silence, blue is louder, red louder still, and yellow and white the loudest. You can also clearly see the bursts of bright colours when transients occur.