Hands on: Improve noisy recordings

Sometimes the recordings you make just don’t turn out as well as you would have liked. There may be background hiss, clicks, pops or distortion present in the recorded audio, or you may simply be trying to record something in a hostile environment such as a busy street, an airport or even on a noisy telephone line.

Other times you inherit recordings that are noisy and have to work with the consequences. If at all possible it’s best to try to record the piece again, but often this isn’t an option, so you need to switch to rescue mode and start looking for a way to salvage the contents of the audio file.

Thankfully today’s sound-editing software tends to have quite a comprehensive range of tools that you can use to remove various background noises. These range from easy-to-use plug-ins such as noise gates to much more complex noise-reduction tools that take a digital footprint of the background noise and then use complex algorithms to try to separate it from the main audio signal.

But while noise-reduction tools have become much more impressive over the years, you still have to be realistic about their abilities. You’ve heard the saying that you can’t turn a pig’s ear into a silk purse, and the same holds true for noise reduction.

If the signal is atrociously bad in the first instance, no amount of tweaking is going to turn it into a pristine audio file. You may have seen noise-reduction tools work wonders on TV shows such as CSI, taking a barely comprehensible audio track and making it sound as if it was captured in a recording studio, but in real life this never happens.

You can often remove significant amounts of hiss, hum, crackle and pops, but the worse the original signal is, the less likely you are to get good results in the final processed signal. But that’s not to say noise reduction is a lost cause. Often it can work wonders – ­ you just need to be realistic about what’s possible before starting out.

The spectrum of noise
What makes noise reduction such a tricky process is that noise usually comprises lots of different types of sounds, with different frequencies and timbres all mixed together. Often it hops around the frequency spectrum, jumping from low- to high-frequency sounds and everything in between.

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