Good candidates for the hard limiter.

At times there is a need to reduce the dynamic range (the difference between the loudest and softest sounds in a message) in order to provide a useful listening experience for those listening to these messages in a car, on headphones, or on their computer.

Most music CDs are mastered where one of the processes is to boost the sound while making sure there is no clipping, resulting in a decreased dynamic range. Similarly, radio stations employ an expander / gate / compressor / limiter to reduce dynamics and increase the overall volume to the live stream and when preparing programs.

You must be careful as you do this reduction in dynamic range to avoid removing the normal and intended variations in volume that are used for emphasis, reducing the dynamic range so much that the emphasis is lost.

We generally do this by bringing the lower peaks down and then use a process called Normalization up to -1dB. The hard limiter can be of great help where there are many high spikes in volume but much of the message is much quieter. Here are a two examples of messages where the hard limiter should be useful.

Here is the second file after the hard limiter has been applied:

Pretty nice looking isn't it? And it only took the computer a couple of minutes to do this. Read further because you may be looking at those green areas that look flat at the -1dB line and think they are clipped. They are notclipped. It is just that there are may peaks of the waves at -1dB close together. When zoomed in they are at or beneath -1dB; when listened to, it sounds fine.

Some files have an even greater difference between the high volume portions a the low volume portions. If there are any peaks that are clipped, the clip restore must first be used to restore them.

The hard limiter button is just to the left of the normalize button. It looks like an upside-down green, somewhat uneven letter U.

Another consideration before boosting the volume on a file is to determine if the background noise is low enough to boost the sound. Here is a screen-shot of the background noise in this file before the hard limiter was used to boost the volume and reduce the dynamic range.

As the curser is looping around, there is no sound that is much greater than -58dB and most of it in this section is less than -60dB. It is good practice to select small portions of the file that show the highest and lowest volumes and test various settings. Also, check to make sure that the emphasis the person speaking intended with their change in volume is not taken away by too much hard limiting.

This may take a bit of trial and error, so be patient. I have used as little as 3dB boost and as much as 14dB boost. Everything depends on the file and the testing of small portions to see what sounds best.

Be sure to check the residual background noise on these tests. If the end result is too high (greater than -42dB is my general rule of thumb) then do noise reduction before using the hard limiter as this gives the best results, at least it has in my testing.

When I am finished testing I then click some place in the file to remove any highlights of small portions and then I set the settings as you can see.

This particular file needed a greated deal of boost to the sound, so I chose to Boost Input by 14dB. I wanted the maximum amplitude (max volume) to be -1dB, which was set accordingly. All the other settings were left as default.

Here is what the file looked like about two minutes later:

Now, before you panic because it looks clipped, notice the highest sound is -1dB. How the hard limiter works is that it takes each sample (44,100 samples per second) and tries to add the boost I selected, in this case 14dB. But, this is the key, if the resulting volume would be above the maximum amplitude I set, then the hard limiter recalculates how much volume to add to the sample to bring it up to -1dB.

This process is repeated point by point for each sample throughout the entire file. If nothing clipped before the hard limit, nothing will be clipped after the hard limiter is applied.

Here is the background noise after the hard limiter did its work on the same section of background noise we looked at before:

-48dB is totally acceptable. This file is now ready for the rest of the traditional editing techniques such as one second of silence at the beginning and end of the file, reducing any pauses greater than three seconds.

If this is to be edited to Conference Editing standards, you are done.

If this is to be edited to more stict standards like radio, podcast, website, etc., then you are ready to start listening through the message and fixing the other little things you have been led by the Spirit to fix.