Reducing Noise in Audio Files

The beauty of digital audio is its promise of pristine quality.
No clicks, hiss or scratches that were the norm of vinyl and
tape recordings. That’s not to say that all digital audio is
noise-free. Far from it. Poor recordings can still be made in
the digital medium and recordings that have been transferred
from analog (vinyl records or cassettes) to digital will retain
some of their noise.

Fortunately, cleaning up digital audio is a fairly easy process.
There are many software packages on the market specifically
designed for reducing specific types of noise in digital
recordings. Not all of them are suitable for all types of noise,
so it’s important to analyze the type of noise you are trying to
get rid of.

Most noise reducing software has a function for removing
background hiss. This works by capturing a profile of the
background noise. The profile is used to create a filter that
matches the characteristics of the noise. To use this function
you must select a quiet section of the audio to get a sample of
the noise you want to reduce. A good place to take your sample
from is between songs or the first second or two before the
audio actually starts. The sample does not have to be long –
half a second is all you need – but it can’t be music or voice –
it should represent a silent section.

This noise profile will help you to reduce exactly the right
kind of noise from your audio recording. It is useful for
reducing background hiss, but clicks and pops need another kind
of processing.

Pops and clicks are of two flavours – digital and analog.
Digital clicks can be caused by processor overload as you make a
digital recording. The recording “stops” for a moment and the
resulting skip creates a very short click. Digital clicks are
easy to detect and most noise reduction software does this
automatically. 

Analog clicks and pops are caused by scratches and imperfections
on vinyl and their duration is much longer than digital clicks.
To remove this type of noise, a special filter is needed to
automatically detect and remove the unwanted sound. Settings can
be adjusted to match the size and frequency of the noise.

There are several audio packages on the market that are
specifically designed to reduce noise from vinyl and cassette
recordings. They allow you to capture the audio digitally by
connecting a turntable or cassette deck to the sound card on
your computer. Once the audio is stored on the computer, it can
be processed to remove background hiss and clicks. Most presets
will give you adequate results and you will be able to enjoy
your old recordings in the digital domain.