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.