Digital voice recorder resting on an old book

Audio evidence is only as good as the quality of the recording; hiss, muffled sound, dips in volume and other sonic imperfections can take a high-quality piece of evidential audio and render it useless. That's why audio enhancement software can be so handy. Before making any audio recording that involves other people - whether they are aware they are being recorded or not - consult this guide on the legalities of surveillance equipment. It will explain where you stand legally if you need to record someone.

Once you've made your sound recording, you may be disappointed with the results. Walls - assuming you're trying to record through one - are an obvious barrier to audio perfection. Sadly there's not a lot you can do about walls aside from investing in some of our laser-guided audio recording equipment. But a few factors within your control enhance or diminish the quality of your recording.

Getting the best recording environment

Before you even take your microphone out of its box, consider the environment you are recording. Here's a list of things that are bad for recording;

  • Mirrors, tiles and other reflective surfaces
  • Open windows
  • Equipment with moving parts, such as fans
  • Beeping, buzzing or otherwise potentially infuriating devices
  • Equilateral walls - granted, there's not much you can do about this

And here is a good way to mitigate these problems

Reflective surfaces - cover these or remove them. Take mirrors out of the room, close curtains to conceal glass and drape as much soft fabric, such as old sheets, around the place as possible. Record producer John Leckie, who produced Radiohead and The Stone Roses, among others, famously brings in soft furnishings from his house into the studio to deaden the sound. Open windows - close them! Equipment with moving parts - Turn off the air-con, toilet fans and actual fans. If your computers fan is super loud, consider recording directly to a hardware-based recording device and then uploading that to your computer later.

Beeping and buzzing - very simple, put phones, tablet devices and any non-essential tech in another room. Equilateral walls - Go to any pro recording studio, and you'll note the control room has sloping, uneven walls. Wall reflections are only really relevant if you're using the sound recording for commercial releases, and even then, it's not a massive issue. But if you're an audiophile who wants to avoid those pesky bass traps and unwanted audio reflections, invest in removable baffles or stick some egg boxes to your wall.

Removing hiss from an audio recording

This is a post-production job, meaning you do it after you've captured your audio. Using the equaliser tool on your audio software (for more on audio software, check out our previous article on recording through a wall using a microphone), you can amplify or reduce the volume of certain frequencies. Unless you want to get geeky about it and learn the precise frequency of this precise audio hiss, drag the equaliser curve around the screen until the hiss abates.

Enhancing speech in an audio recording

Just as you dragged the eq curve around the screen to reduce hiss, you can do it enhances vocal frequencies, which is ideal for improving the clarity of someone speaking. Just be careful you dont reintroduce hiss to the recording.

Increasing the volume of an audio recording

If you want to make the overall recording seem louder (note; it's impossible to add volume to a recording, but you can add the perception of volume), use the onboard compression tool. This not only increases perceived loudness but also improves clarity. It boosts low and limits high signals, so the overall mix is more consistent, making it easier to listen to and removing any horrible spikes in volume.

Editing an audio recording

Once you've got the overall sound quality the way you want it, you may wish to remove unnecessary sections or cut out key sections to add to a separate file. Look for the scissors icon. This is the universal symbol for the trim or cut tool. Once you've selected the scissors, click on the audio file to select the first trim point and click again to mark the second. Everything in between these two points will be cut. Then use either copy, cut or delete to perform your desired action. Now the sound is how you want it, and you've selected and isolated the important bits; you've got some very useful audio evidence in a format that's easy to share, send and store.

The best way to export such data is as an MP3. If you need better quality, export as .WAV, but these files can be large and take longer to send. And remember to save as you go.