During mixing, we can use a compressor to even out differences in level. This is one way of helping a vocal sit nicely on top of a mix by ensuring that quiet, subtle words or phrases are loud enough to be understood with clarity, while louder sections don’t suddenly jump out and overpower everything else.
How we choose the compressor settings depends on the effect we want the vocal to have and on the style of the arrangement and instrumentation of the music.
In the album version of the song “The Writing’s on the Wall” by iZotope friends OK Go featured in the video above, the lead vocal is compressed aggressively, likely with settings similar to these:
You can hear the compression by listening for the accentuated breaths during the verses, the fast and drastic reaction of the compressor to loud plosives on P and B sounds, and the consistent level of the vocal throughout. All of this combines to a significant amount of gain reduction, and then a relative amount of makeup gain to help the vocal sit on top of the dense arrangement. These compression effects work well in this rock context, but might sound out of place in a more stripped-down acoustic version.
If we listen to that same song performed by the band acoustically, we can hear a more subtle, natural-sounding vocal. There is likely some gentle compression on each of the vocalists’ microphones, perhaps with settings like these:
This means that the vocal is going to be more dynamic, but still sits nicely on top of this arrangement and instrumentation, and still without peaks overpowering the mix at any point. This is especially important in a live broadcast situation like in the video above (recorded by 89.3 The Current in Minneapolis/St. Paul).
To get started with compression for your own vocals, first get the best balance you can between the lead vocal and all the other instruments without using any compression, accepting that a few words may sound too loud. If there are large changes between sections or phrases, like a loud chorus versus a quiet verse, consider adjusting the gain of these clips individually to make broad adjustments and get a generally even delivery. Then, you can use a compressor to attenuate just the peaks without making the compressor work too hard.
Depending on the style of your music, you may want to begin with more aggressive settings for a dense mix and more modest settings for a dynamic mix. For an aggressive vocal, start with a ratio of 4:1, and gradually bring the threshold control down to engage the compressor. For a more mellow vocal sound, start with a ratio of 2:1, and gradually bring the threshold control down to engage the compressor. The lower the threshold, the harder the compressor will work. The higher the ratio, the harder the compressor will work. Find a balance between the threshold and ratio to get the basic sound you want, before adjusting any of the other parameters.
Once a compressor starts working, it will begin reducing the level of the signal and may make your vocal sound quieter. You can compensate for this by using the makeup gain parameter on your compressor. Some compressors even have an automatic makeup gain feature that will add level after the compression has been applied in proportion to how much compression is used.
Once you have the threshold, ratio, and makeup gain set to an approximate starting point, it can be time to start adjusting other parameters like attack and release. It’s important to understand that all the settings on a compressor are interrelated, so changes to attack time may mean you want to adjust your ratio, or vice versa. Attack and release adjustments will likely sound more subtle than threshold or ratio adjustments, so it can be good to think of these as “fine” adjustments after you’ve gotten the basic sound you want.
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