Noise cancelling headphones remove background noise by comparing a desired signal to a perceived signal and removing the unwanted components. So for noisy situations where we don’t have access to the clean signal, are we stuck with just the noisy signal?
Not necessarily.
Audio editing tools like Audacity can also be used to remove constant background noise from an audio track by building a simple model of the noise component and then removing it from the audio track.
The following tutorial shows how a low level of background noise may be attenuated by generating a model of the baseline noise on a supposedly quiet part of an audio track and then removing it from the whole of the track. (The effect referred to as Noise Removal in the following video has been renamed Noise Reduction in more recent versions of Audacity.)
SAQ: As the speaker records his test audio track, we see Audacity visualising the waveform in real time. To what extent might we consider this a form of augmented reality?
Other filters can be used to remove noise components with a different frequency profile such as the “pops” and “clicks” you might hear on a recording made from a vinyl record.
In each of the above examples, Audacity’s visual representation of the audio waveform, creating a visual reality from an audio one. This reinforces through visualisation what the original problems were with the audio signals and the consequences of applying the particular audio effect when trying to clean them.
DO: if you have a noisy audio file to hand and fancy trying to clean it up, why not try out the techniques shown in the videos above – or see if you can find any more related tutorials.
Digital Worlds - Distorted Reality 
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