Removing Audio Problems Part 2: Removing Hiss

Recently, I posted an article about the basics of removing audio problems, and the limitations that you face right out of the box when you go to fix some nasty audio. This time around, we are going to talk about removing a very specific type of audio problem: hiss.

What is Hiss?

Not to be confused with hum, hiss is a persistent noise on a recording that sounds like … well … hiss. Turn the sound up loud enough and you will almost always here some on your recording. A low levels, it isn’t much of a problem.

The problem is when you have hiss on a recording that is distracting – say from a bad microphone or from turning up low dialogue. You could also be trying to restore an old recording that has hiss on it. Wherever it comes from, however, it’s annoying and needs to be destroyed.

The Basic Method of Getting Rid of Hiss

Hiss removal involves a few similar steps no matter what software you are using. First of all, you need to find a sample of hiss just by itself. That way the audio program knows what the hiss actually sounds like isolated – before that, it could get hiss confused with other parts of your recording. After setting some parameters, your tool of choice will try to remove that hiss from the recording without damaging any other areas.

To illustrate, I am going to take a look at removing hiss from two programs: Audacity and iZotope RX.

Removing Hiss with Audacity

If you are not familiar, Audacity is a great (and free) audio tool for Mac and PC. You can get it here. To get started, open it up, and import a piece of audio.

After importing your track, look closely for a small chunk of audio where there is only noise. After you’ve found it, select that portion of audio.

Select Noise Removal… out of the drop down list of effects from the Effects menu. This will give you a little dialog box that presents a handy two step guide. The first, is to get a noise profile. Since we’ve selected our noise profile area, we can just click the “Get Noise Profile” button.

Once you have the noise profile, deselect the noise profile area, and get back to the two step panel. You can adjust the noise reduction amount, preview it, and hit okay. Play back your audio, and the hiss is now minimized or gone.

As we mention in our limitations section, your audio may be affected depending on the Noise Reduction level you’ve chosen. If you are getting audio that sounds like it was recorded underwater, it is time to go back and rethink your parameters.

Removing Hiss with iZotope RX

iZotope RX is a fantastic program that is well worth the fact that it is not free. You can get it at BHPhoto.com.

What does iZotope RX have that free solutions don’t have? Well first of all, it can do a lot more than take out hiss, but we are sticking to hiss in this article. One of my favorite features of iZotope RX is its Spectrogram information. It can be viewed right on top of the more conventional wave pattern:

This view allows you to see – in much greater detail – disturbances or irregularity in audio. For instance, hum can be observed as a single line shooting horizontally through a recording. Hiss appears as “noise” you can see in the background of the audio.

Removal works in a similar fashion to Audacity. Find a portion of the audio where just the hiss is present, click the Denoiser button and click Train. This will “train” the program in the audio noise profile of the recording.

As in Audacity, you have a Noise Reduction level and a Smoothing option. However, you also have a choice of several algorithms that might give different results. Some take longer to process, but it is worth it to see which one might fit your situation the best.

When using an advanced program like iZotope RX, it is a good idea to look through their documentation. In the case of iZotope RX, the documentation happens to be extremely helpful and thorough.

Limitations

Of course, there are limitations. Like we mentioned in our previous post, audio is like a bowl of soup. You are going to take out some things you want to leave in. Since every piece of audio is very different, you’ll need to do some experimenting with parameters to see what level of removal leaves your audio suitably in tact.

via Removing Audio Problems Part 2: Removing Hiss | DiY Filmmaking.