Fixing poor location sound can be a challenge, but the right tool can get you there in minutes.

What Kills Location Audio?

Sound sources recorded on location can be compromised by a combination of external factors including noise, poor acoustics, or equipment (either in its use or occasionally its quality). This is perhaps most noticeable on dialogue owing to the listener’s ability to know instinctively when something isn’t right with a human voice.

We have tools to deal with artefacts such as electrical or acoustical noise, and even the amount of ambience in a recording, but a third factor is comb filtering of the recorded audio. This can be a result of a poor acoustic environment interfering with an otherwise nice, dry, clean voice, but what causes it exactly?

Comb Filtering

Sometimes a location or a particular shot will dictate that a mic ends up placed near a reflective surface. Reflections from that surface will arrive later at the mic than the direct sound does. As well as adding an ambient quality, these will reinforce certain frequencies while cancelling others due to phase differences related to the sound’s varying wavelengths at those frequencies. This scenario is different to a recording that is simply too reverberant, as the reverberation is not correlated to the dry sound.

Most will be familiar with the familiar hollow, nasal, or ‘sucked-out’ sound that comb filtering can bring. In a two mic scenario, combing cannot be fixed by introducing a delay offset to one of the mics because the amount of phase shift at any given offset will be different at any given frequency. The problem can get very complicated when more than one mic is involved, and especially when the source and/or the mic is moving.

This is commonly heard when boom operators ‘drop’ with the subject as they sit down at a large table, for example. This is especially noticeable on fricative sounds rich in harmonic content. For simpler scenarios where everything is static, we can correct a signal’s response with the right tool.

UNFILTER from Zynaptiq

For any mixer contending with the anomalies of a co-produced project, UNFILTER from Zynaptiq is the plugin that can deal with dips arising from comb filtering, and also can even restore frequencies in other sources with seemingly little information left to work with making UNFILTER is an extremely powerful utility for post-production and music mixers alike, and has a unique feature set that makes new ways of working possible:

UNFILTER Features:

• Automatically detect and remove resonances, equalization, roll-offs and the effects of comb filtering from musical, location, dialog and surveillance recordings.

• Apply the measured filter response to other signals to place them in the same "acoustic world".

• Export the measured filter response to or import it from a linear- or minimum-phase impulse response file (WAV).

• Mastering grade adaptive, free-form and graphic equalization.

• Extremely steep 96dB/octave shelving high-pass filter.

• Output limiter for unsupervised use in batch processing applications.

• Highly time-efficient workflow and UI

Killing Colouration

Audio suffering from the effects of comb-filtering will be a fact of life when acoustic environments and mic positioning conspire against us. While flawless production sound is the ideal, we also have the tools to iron out problems that do creep through.