In last article, we talked about the effect of “normalize.” Basically, it takes the maximum amplitude of the signal we are processing, adjusts it to the level that we choose and adjusts the whole signal proportionally. In terms of decibels (db), this simply means adding or subtracting the same amount of db to the whole signal such that the maximum amplitude is at the chosen level.
Next we need to know how Audacity does normalization in a multiple tracks situation.
Figure 1 shows a simple Audacity project with 2 mono tracks. It is taken from one of my instructional videos. The first track (named “My Voice”) contains my voice in a describing tone. The second track (named “music”) is some background music that I chose to use.
You can see that the background music is relatively low in volume comparing to my voice. I usually like to put some background music in my videos because a completely silent background can sometimes sound strange and unnatural. Yet I don’t want the background music to be so overpowering that it competes with my voice, so I typically use low volume for background music.
Now watch the effect when I chose both tracks and then normalize them to a maximum amplitude of -3.0. Figure 2 shows the tracks after such normalization.
You can see that the music tract got amplified a lot. In fact, its volume is compatible to (or competing with) “My Voice” now. This is because Audacity took each track and normalized each of them separately and independently. That is, it took “My Voice,” examined the maximum amplitude and adjusted the whole track so that the maximum amplitude became -3.0 db. Then it independently examined the maximum amplitude of the “music” track and adjusted the volume so that the maximum amplitude of the “music” track became -3.0. That means we lost the relative volume between the 2 tracks.
There is nothing wrong about this, and this is completely described in Audacity manual. We just need to be aware of it.
You could choose to normalize “My Voice” alone, and that would keep the low volume of “music,” but since “My Voice” would be adjusted to become louder or softer, the original balance between the two tracks would become different, so you would also need to adjust “music” separately to maintain the balance.
If you want to adjust the overall volume but maintain the balance among difference tracks, you should use “Amplify” effect rather than “Normalize” effect. “Amplify” effect works very similar to “Normalize”, but “Amplify” maintains balance among tracks.
“Amplify” effects will be treated separately. For now, all you need to know is that “Amplify” and “Normalize” are similar but they treat multiple-track adjustment differently.