The normalize effect is a simple effect to set maximum amplitude to a chosen level. If you think of any audio system, be it a simple CD player or a complex sound system with lots of equipments, the normalize effect is simply the volume control knob. You turn the knob up and down to turn the volume of the sound up or down. It is just that simple.
Such a simple effect hardly needs any explanation, but we will use this effect to illustrate the difference between linear scale and decibel scale (same data but represented in different scaling system). Also, specific to Audacity, we will look at how the effect works for multiple tracks (and related to this, the difference between Normalize and Amplify). We will also look at its use in stereo tracks.
To see how the normalize effect works exactly, I am using a generated track with only two levels of intensity, one at 1.0 and one at 0.5, as shown below. The normalize effect works with peak intensity, so we take note that the peak intensity in this case is 1.0.
Next we are going to reduce the intensity to be half of the original intensity. To do that, we use “normalize” and set the maximum amplitude to -6.0. As mentioned in the article “Use of Decibels“, -6 db means halfing the intensity, so here is the value we enter:
As also mentioned in the article, “Use of Decibels,” sound intensity works in proportion, so it is important to realize we are not subtracting the original intensities by an amount of 0.5 unit. In other words, it is NOT that the original intensity of 1.0 will be reduced by 0.5 and become 0.5, and the original intensity of 0.5 be reduced by 0.5 and become 0! Rather, it is that each intensity is halved (or multiplied by 1/2), so 1.0 becomes 0.5, and 0.5 becomes 0.25. This proportional effect can be clearly see in the waveform shown below.
Now let us examine the same thing in decibel scale. The original waveform has tones of intensity 1.0 and 0.5. These correspond to 0 db and -6 db in decibel scale, as shown in figure below.
When we half the intensity, we reduce all intensities by 6 db. Decibel (or logarithmic scale) converts multiplication to addition and division to subtraction. So if we are dividing all intensities by 2, in decibel scale it simply means we reduce all intensities by 6 db.
Below is the waveform after normalization. Note that in decibel scale, the original magnitude of 0 db becomes -6 db after the normalization, and the original -6 becomes -12.
Normalize effect (without DC offset removal) simply turns volume up or down. As far as actual data is concerned, it simply multiplies or divides all intensities by a scaling factor in linear scale, or add or subtract by a fixed amount in decibel scale.
In most cases of normalization, you probably don’t need to bother with the numbers but can simply listen to the volume. However, understanding how this works can help in understanding other more complicated effects.
I hope this article helps a little in understanding normalization and decibel scale. If you like this article and the series in general, please share and/or like it, and subscribe to the blog. Thanks!