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Tackle "Impossible" Mastering Solutions

June 30, 2014

Fig. 1. In the spectral editor for SpectraLayers Pro, bass frequencies (displayed as red blotches) are painted with a mouse on thin-sounding kick drum hits to make them sound much fuller. The top half of the spectral editor displays the mix’s left channel, while the bottom pane shows the right.

EVERY NOW and then in my mastering work for clients, I’m confronted with a mix that has such a deeply embedded problem that I think to myself, how the heck am I going to fix this?!? Fortunately, there is almost always a technical solution for even the most challenging hurdle. The trick is to analyze the defect in terms of its distinct components, such as its envelope, ambience, and dynamic range, and the frequency band and channel it occupies. Here are three examples of seemingly impossible mix quandaries and their mastering fixes.

Thin Kick Drum With Full Bass Guitar The bass guitar has the perfect amount of low-frequency content, but the kick drum sounds paper-thin. How can I add basement frequencies to the kick without making the bass guitar sound too boomy?

The saving grace of thin kick drum beats is that they typically have shorter sustain than bass guitar notes. So, one cure for this ailing mix is to have a dynamic equalizer briefly add bottom end to kick drum hits and then undo its processing before the bass guitar has a chance to sustain.

The Brainworx bx_boom mid-side plug-in does the job posthaste. Instantiate bx_boom on your DAW’s stereo master for the mix. Set the plug-in’s mode initially to LO. Turn the bass drum (threshold) knob clockwise until the knob flashes on kick drum hits, but not so far as to make the knob constantly glow. Set thus, bx_boom will boost the mid channel’s bass frequencies—centered around 32Hz—for 50ms whenever the kick drum voices and then quickly return to flat response. As you turn the bass drum knob farther clockwise, the amount of bass boost will progressively increase from +4 to +10dB. A knob setting of +40 to +50 (an arbitrary scale) usually satisfies. If the kick still sounds too thin, try using MID (boosting at 48Hz center frequency) or HI (64Hz) mode, as long as that doesn’t audibly reinforce the bass guitar.

If you’re not pressed for time, Sony SpectraLayers Pro offers a more surgical solution in the form of spectral editing. Import your mix into the standalone software, and create a new, empty Layer for adding audio (in this case, additional bass frequencies for the kick drum) to the mix. Select SpectraLayers’ Draw/Frequency tool and, with your mouse, paint a sub-bass tone on each of the mix’s kick drum hits in the GUI’s spectral editor (see Figure 1). It will sound best if you paint a frequency that is the tonic for the key of the song (for example, 65Hz for the key of C major or minor). After you’ve added a subbass tone to each and every kick drum hit, adjust how loud you want the tones to be en masse by raising the fader for their layer in the Layers side panel. The entire process is time-consuming and painstaking, but done correctly, the kick drum hits can be made to absolutely thunder without audibly affecting any other element of the mix.

Boomy Kick With Balanced Bass Guitar This problem is the opposite of that in the preceding example. bx_boom is once again the antidote. To attenuate only the kick drum’s bottom end—without noticeably affecting the bass guitar’s—turn bx_boom’s bass drum knob counter-clockwise until it flashes on beater strikes. As you rotate the bass drum knob farther counter-clockwise, attenuation of bass frequencies will progressively increase from –4 to –10dB (attenuating for only 50ms with each beater slap). A knob setting between –40 and –60 will usually winnow enough rumble from the kick drum to make it sit pretty in the mix.

Lead Vocal Is Too Dry Adding reverb to a mix will lend vital wetness to a desert-dry vocal, but it will also unpleasantly reverberate other elements such as the bass guitar and cymbals. Assuming the cymbals were miked in stereo with a spaced pair of mics, you can add reverb to only the mix’s mid channel to isolate the cymbals from the reverb. However, the center-panned bass guitar will still sound like it’s playing in a subway. Are we at a dead end? Nah.

The remedy is to filter the mid channel’s reverb to weed out the bass guitar (and, while we’re at it, any unwanted instruments voicing above the vocal’s frequency range). iZotope Ozone 5 is the magic bullet. Insert Ozone 5 on the mix’s stereo master, and assign its reverb module to the mid channel in mid-side mode. Drag Ozone’s high- and low-frequency cutoff nodes in the plug-in’s Mini-Spectrum Window (at the top of the GUI) to create a bandpass filter for the midrange. Reverb will be added to the lead vocal and any other center-panned, midrange elements (such as electric guitar) but will virtually leave the rest of the mix untouched. Mission Impossible accomplished!

Michael Cooper ( has written more than 400 articles about pro audio over the past 25 years.


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