Parallel filters

A parallel 12dB/oct high pass at 2kHz at unity gain produces a 6dB high shelf boost and a 2dB cut at 1kHz. At a 6dB/oct slope, the phase shift almost doesn’t matter anymore, with the corner frequency effectively shifting a little lower.¹

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Use a parallel high pass to apply a shelving boost to multiple channels at once, with the added flexibility of controlling how much gain of each channel you send to the parallel high pass.¹

A parallel low pass with a 12dB/oct slope has an effect like the Pultec low end trick. When applying dynamic processing to this shape, a compressor turns into an expander at the dip just above the corner frequency, where the two are summed.¹

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Parallel bandpass filters are especially useful for bringing out more fundamental in your drum shells.²

Flip the polarity of a parallel bandpass filter to produce a hard notch at the corner frequency. Turn down the volume of the parallel track to turn the notch into a cut. Turning down 6dB creates a ~6dB cut. Turning down 12dB creates a ~3dB cut. Send anything that you want to cut to this track. To make it dynamic, a downward expander becomes a downward compressor after the polarity is flipped.³

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Use a parallel band-pass filter to boost and cut two tracks. Send both to the parallel channel with the polarity flipped on one. This results in a bell boost for one track and a notch for the polarity-flipped track. Back off the send gain to the notch track -6dB to turn it into a 6dB bell cut. Adjust the fader to dial in the cut and boost. Dan Worrall then uses a downward expander to dynamically ride this frequency region and allow each part to interact.⁴

Send both to the parallel channel with the polarity flipped on one. This results in a notch filter for one track and a bandpass filter for the polarity-flipped track.⁴