Removing excessive natural reverberation in audio post

One problem that you may encounter in audio post work is a large amount of natural reverberation recorded on the sync tracks. In the worst case this will make your dialogue difficult to understand as well as give you problems to match other (more closely mic’ed) dialogue to it.

In this post I want to share two approaches to diminish this natural reverberation on the track leaving you with cleaner audio to work with.

Solution 1: Expanding

You’ll need a downward expansion plug-in (ie a gate that has a ratio setting) such as Avid’s Expander Gate Dynamics III. Use a low ratio (1.1 – 1.4), fast attack and set the threshold to 0 dB. Leave hold and release relatively short. You will notice that the reverb tails at the end of words drop significantly. Of course this does not remove early reflections, but at least it kills annoyingly long decay times, leaving you with more intelligible dialogue. The higher the ratio, the more intense the effect.

Removing reverb tails on sync sound using a gate

Solution 2: Using phase-inversion, EQ and compression

This is slightly more complicated but gives you more freedom with regards to which frequencies you want to affect. In the screenshot below, I have duplicated my problematic track and processed the audio on the duplicate using an equaliser with just the phase-inverter switched on. Playing back both tracks you should hear – nothing (if you still do, check that all automation on both tracks is the exactly the same).

Original and phase-inverted track

Now, add a compressor to the phase-inverted track, use settings like these (important: fast attack, low threshold, low ratio):

Compressor setup

If you need a more agressive effect try to raise the compression ratio (you will first notice that the sound becomes more and more similar to the original since you are adding less and less of the phase inverted signal) and then raise the output gain of the compressor until you are satisfied with the result. Here’s an example:

More extreme compression settings

Last but not least: If you want to tweak the frequency response of your effect, insert an equaliser before the compressor. Experiment with low- and high shelves for a start and see how they affect the sound. Interestingly, if you shelve off the highs of the phase-inverted track the low and mid-frequencies become more accentuated and vice versa.

Finally, here’s a screenshot showing the original audio on top and the three approaches discussed (simple gating, phase-invert and compress with low ratio and phase-invert and compress with high ratio) below.

Reducing reverb tails - results

That’s it for now – I hope you liked the read. If you’ve got any feedback or want to discuss results, feel free to leave a comment!

Signing off…

Norbert