Video Recording: Improving Sound Quality – Basic Noise Reduction

tware. This article focuses on how to reduce noise in video that has already been recorded; the other two articles are on:

(I’ve noticed that some people have arrived at this page by searching for information that isn’t included here, but that I may be able to provide. If the information you are looking for is not here, leave a question in a reply/comment and I’ll do my best to answer it).

The first thing to consider is whether it is practical to even try reducing the noise. If is quite easy to clean up constant, steady noises like hums and hisses with freeware programmes such as Goldwave and Audacity. However, If you want to get rid of sounds like someone talking during a piano recital, a baby crying during a wedding ceremony or a plane passing overhead, you will need to get more specialized audio spectrum editing software like Spectralayers Pro, which is not particularly easy to use.

Rather than try to reduce sound later, it’s always better to try to tackle noise during the recording process. Sometimes, however, that’s not an option; we just have to work with what we have.

Why is it Difficult to Remove Noise?

It is helpful to understand a little acoustic theory before trying to reduce noise. If we play Concert A on any musical instrument, the frequency of the sound waves of the fundamental tone of that note is around 440 hz (or 440 vibrations per second). Concert A on a piano and concert A on the violin have the same fundamental frequency, but the two instruments sound different. This is because the sound being produced is  made up of the fundamental tone and a large number of overtones. The frequencies, amplitudes (i.e., strength) and shapes of these overtones give a piano, violin or your own voice its characteristic sound (or timbre).  This is why when you try to reduce background hisses by reducing the level of high frequencies, for example, you affect almost everything else in your audio clip—you are also altering the overtones of things like the human voice, which is why you can sometimes end up with a heard-over-the-telephone voice or a robotic sound instead of natural human voices.

Removing Hums and Hisses

Fortunately, a very steady noise in the background—like the sound of an air-conditioner or fan—can be reduced significantly. For that kind of noise, you can try using the noise filter in your video editing programme, but you will probably get much better results if you use audio editing software such as Audacity (freeware) and Goldwave (shareware) or software specifically designed for noise removal  such as Magix Audio Cleaning Lab (commercial software).  Use your video editing programme to export the audio file or to render the audio part as a separate file. You can also open some video formats in audio editing software like Goldwave and save the file as a WAV file.

Once you have opened the audio file in your audio editing programme, locate the noise reduction function (In Goldwave select Effects → Filter →  Noise Reduction; In Audacity, select Effect  → Noise Removal). Once there, you will see various presets that might prove useful (e.g., Reduce hum, Remove hiss) . However, I would recommend trying the Use Clipboard function in Goldwave or its equivalent in Audacity—Profile Noise Print. To do this, you need to a short segment that contains only the noise you want to get rid of (i.e., you can just hear the hiss or hum; no one is speaking, no music is playing)—a little less than one second will be enough, though in general, the longer the selection of consistent and continuous noise the better. Select that part (just hold down your left mouse button and drag).

What the Use Clipboard / Profile Noise Print does is digitally remove from your recording the part of the audio signal that matches the selected noise sample. To me this function is like magic; I learned about audio recording using analogue equipment (like reel-to-reel tape decks), and to be able to remove noise this easily digitally never fails to amaze me. It still isn’t perfect—if you don’t have strong enough reduction settings, you will get chirping noises in the background, and if the settings are too strong, you will affect the original timbre of the voice of musical instrument—but it is still an amazingly effective way to eliminate noise.

In Goldwave, you need to copy the segment you selected (Ctrl-C or Edit Copy) to the clipboard. After copying, select your entire file.  Then, open the noise reduction dialogue box and select the  function Use Clipboard. Adjust the various settings to find the ideal amount of noise reduction  (Click on the play icon in the noise reduction dialogue box to hear the effect. Unfortunately, you need to re-click the play icon whenever you change one of the settings). Select OK when you are done. The whole process is shown here:

In Audacity, the process is similar, but you don’t need to copy the selection. Just select the sample then go to Effect Noise Reduction Noise Profile Get Noise Profile.   After getting the profile, select your whole file then return to the Noise Reduction dialogue box to adjust the settings and apply the effect.The whole process is shown here: Audacity:

You can also use this noise-print removal function with Magix Audio Cleaning Lab, which is very effective at reducing noise and enhancing audio quality. I recently used it to remove noise and enhance the quality of some music I had recovered from twenty-year-old cassette tapes and thought it did a great job. The software offers finer levels of control than Goldwave and Audacity, making it easier for you to avoid the chirping effect mentioned earlier. Also, when using this software, you can hear the results of any changes in setting on the fly’ (i.e., in real time), whereas in Goldwave or Audacity, after you change a setting, you need to audition (i.e., preview) the sound.

If you are using Premiere Pro for video editing and have Adobe Soundbooth installed, you can also the noise print removal function of this software. In Premiere Pro, just right-click on the audio clip in the timeline, select Edit in Soundbooth and then Render and Replace and your audio file will open in Soundbooth. Select a short clip of the sample noise and then select Processes and Capture Noise Print. Select the whole clip and then select Processes and Reduce Noise. Soundbooth, however, doesn’t give you as much control over settings as in the other software programmes.

Some noises bring their own problems. For example, the noise of a passing traffic may seem like a steady sound, but if you remember you high school lessons on the doppler effect, you’ll also remember that the frequency of objects moving towards and away from a listener will change as the soundwaves are compressed and stretched out. The sound may not be as constant enough to allow you to use a noise-print noise reduction method.

Reducing a Sudden Click

If the sound is really short like a click, I will usually use Goldwave, zoom in on the click so that I can see on the waveform exactly where it begins, select that part and reduce the volume of that by about 70%. The click will still be there but it will be less noticeable. If you reduce it by 100%, you will get a short burst of complete silence, which might be as noticeable as the short click. Magix Audio Cleaning lab also has a de-click function specifically designed for this purpose. You can control how aggressively the software seeks out and eliminates clicks.

Reducing Isolated Sounds

What if you want to reduce the volume of something like a baby suddenly crying during a piano concert? You will probably need to get specialized software for this (and this kind of noise removal is not at all easy).

Using Purchased Software

You can use audio spectrum editing software; these are programs in which you work with visual representations of the audio waveform. For example, you can use Sony’s Spectralayers Pro’s Extract Harmonics tool or Extract Shape tool to visually identify and extract an isolated sound. In their review of the software, MusicRadar writes: “success is entirely dependent on your ability to select the offending frequencies, and that can take time. Once that’s done, though, the results are often excellent.”

Using Freeware

The quick and dirty method is to simply reduce the audio level (fading out and fading back in) and making the part where the baby screams quieter.

Another method would be to apply a form of equalization. You can try (with try being the key word here) using what is called a spectrum filter to identify and decrease the levels  of the frequencies associated with the baby’s scream. You are not just looking for at a fundamental tone (i.e., the ‘musical’ pitch) of the baby’s scream, but you are also looking for the overtones that make the baby’s voice sound different from that sound of a piano. You would visually compare the frequency spectrum of the piano before the scream with the spectrum of the combination of piano/scream. You might be able identify which frequencies are associated with the baby and apply notch filters to those frequencies (a notch filter decreases a very narrow range of frequencies). The following shows an example of a spectrum filter (from Goldwave) with the frequencies around 550 hz and 2kz being sharply reduced (using two notch filters).

Goldwave Spectrum Filter

The chances for success (i.e., piano unaffected and screaming diminished) using freeware programmmes, however, are not great.

Other Ideas

There are other things you can do to handle background noise in your video besides removing it. For example, you can cover it up with something else like music to make it less noticeable. In some situations, you can even add more noise to make it seem like the noise belongs there. For example, let’s say you are editing a street interview and you have to re-record the interviewer’s part later at home on in the studio. If you cut between the interviewer (with almost no background noise) and the interviewee (with lots of street sounds in the background), the contrast will be very noticeable. You can mix some ambient street noise into the edit to make the background sounds more consistent and therefore less jarring (this is  why its a good idea to record some ambient sound whenever you are doing video recording).

Further Reading

~by longzijun


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