What is Normalization?
It is not uncommon for audio engineers to receive audio for mixing that has been recorded at low volumes. Many amateur audio engineers might, in an attempt to increase the loudness of an audio clip, just place a limiter on the channel strip and crank up the gain. This is detrimental to the mixing process as it might negatively alter the dynamics of the clip if other parameters of the limiter (ratio, threshold, attack and release) are not adjusted. For this reason, professional engineers might opt to use normalization.
Normalization is a volume adjustment feature that is present in every digital audio workstation on the market. It is used by engineers and producers to increase the overall loudness of a clip or increase the loudness of part of the clip to a target loudness thatis measured in Decibels relative to full scale (dBFS). It does this in such a way that the dynamic range of the audio is not adversely affected since both the highest and lowest peaks are adjusted by the same degree when the normalization process is applied.
How Does Normalization Work
Normalization plug-ins function by analyzing audio files in either one of two ways. The first way is by analyzing the peaks of the audio clip to find the highest one. This is referred to as Peak volume detection. The second is that they analyze the clip to determine the average loudness of an audio clip. This is referred to as RMS Detection. Which of these detection methods an engineer applies is largely dependent on the type of audio file they are working on. Let us look at the practical applications of each of these methods
Peak Volume Detection
Peak Volume detection assesses an audio file to find its highest peak. Let’s assume that an engineer sets a target loudness of -6dB and the highest peak of an audio file is at -12dB, then the loudness of the entire audio file will be raised by 6dB. Peak normalization is best suited for tracks with sharp transients. As such, peak normalization is best used on drum tracks or, to use a non-musical example, it could be used on sounds such as punches or gunshots. It is best used on individual tracks in a mixing session. In most cases, a target level of 0dB is used as a default. Some normalization plug-ins may not offer the option to adjust the target loudness. There are some drawbacks to using peak normalization. Despite the fact that an audio clip may sounds nice and loud when normalized and played in solo mode, there is the possibility that normalizing to 0dB causes clipping on your master channel. For this reason, it is advisable to use normalization sparingly.
RMS (Root Mean Square) Volume Detection
This detection method assesses the audio clip for the highest and lowest peaks and finds the average loudness of the clip. The clip can then be processed to bring the loudness up to the desired target level. Some engineers use this to increase the loudness of audio that does not have sharp transients for example when editing ambiences or during mastering.
How to Normalize in Pro Tools
Now that we know what normalization is let’s see how we can use the Normalize function in the pro tools audio suite.
Step 1 – The first step is to select the audio to be processed. This can be done from either the edit window or by clicking the track name on the clip list.
Step 2 – Open the AudioSuite menu and then open the Other sub-menu. Here is where the Normalize plug-in can be accessed from.
Step 3 – With the Normalize window now open, the parameters to be used for normalization can be adjusted.
From the screenshot above, the options marked with numbers represent:
- Plug-in selector. This can be used to select a different plug-in if one opts to use a different plug-in from the audio suite instead of “Normalize”.
- The Selection reference. Here we can specify whether the normalize plug-in uses the selection in the playlist or the one in the clip list
- The Use in playlist control. When selected (highlighted in blue) will do one of a few things.
- If the selection reference is set to Playlist, then the audio clips n the playlist will be replaced by the normalized audio once the Render button is clicked.
- If the selection reference is set to clip list, all instances of the selected clips that appear throughout the session will be replaced.
If the use in playlist option is not selected, the newly rendered audio will appear in the clip list but will not replace the one(s) in the playlist and will thus have to be placed in the playlist manually. The use of Spot mode may come in handy here. In most cases engineers have the use in playlist feature selected.
Step 4 – Select an Output mode from the Processing Output Mode Selector.
Here there are three options to choose from.
- Overwrite files- As the title implies, selecting this option will permanently replace the audio files on disk with the newly rendered, normalized files. This process is destructive and thus irreversible. This is why Pro Tools brings up the following dialogue box if the render button is clicked while this option is selected.
The destructive nature of this output mode is why it hardly ever used by audio engineers.
- Create Individual Files- Use this option if your selection is of more than one clip and you wish for the rendered clips to remain as individual clips such as in the example below where clicking Render would result in the two selected clips a and b being normalized and rendered as two separate audio clips.
- Create Continuous File- When applied, this option will result in a single rendered audio file. Any gaps between clips will be automatically filled with silence similar to how gaps are filled when consolidating clips.
Step 5 – Select a Processing Input Mode from the Processing Input Mode Selector. This selector determines how the normalize plug-in will perform its analysis of the selected audio clips. It offers two options.
- Entire selection- With this choice selected, the normalize plugin will treat the entire selection as if it were one clip. The loudest peak among the selected clips will be used as the reference point therefore all the selected clips will have their loudness increased by the same amount.
- Clip by Clip- Selecting this option tells the normalize plugin to analyze each clip individually. This means that the increase in loudness will vary from clip to clip even though the target loudness will be the same value for all selected clips.
Step 6 – Use either the slider or the text box to set a target loudness.
Step 7 – Click Render to render the normalize audio files based on the parameters selected in the steps above. Upon doing so, it can be noted that the names of the newly rendered files will have the letters “NORM” appended to them.
In conclusion, we can see that the normalize function in Pro Tools is used to increase the overall loudness of selected clips to a target loudness without altering the dynamics of these clips. It can be a faster alternative to slicing and clip gaining the audio clips in a session. Also, being an Audio suite plugin, it does not process audio in real-time thus allowing engineers to render entirely new audio files once the processing is complete. Normalize is a great tool to have in your audio engineering arsenal.