It's not only mastering engineers who apply subtle EQ adjustments to the full mix, experienced mixers like Mick Guzauski will often add some EQ on the master bus. In this excerpt, from the third installment of the "Lifeboats" series, "Mick Guzuaski Mixing Lifeboats," you'll see a couple of different EQ plug-ins used to gently augment the overall frequency signature of the song.
SHELVING UNIT
Guzauski starts out by opening a Sonnox Oxford EQ and Filters plug-in. He initially says he's going to put in a 20Hz high-pass filter, which will roll off audio below that. But then he changes his mind, saying that the Juno synth part that's a critical part of "Lifeboats," contains some subsonic information, and he likes the way that sounds.
Guzauski turns his focus to the high end of the mix, and after listening again, he uses the Sonnox to add a 1.25dB high-shelving boost at 5024Hz and a 1.06dB boost with a peaking EQ at 5760Hz. Notice that he makes his adjustments in real time, as he's listening.
Guzauski ended up with these settings on the Sonnox Oxford EQ
Next, he inserts a UAD Manley Massive Passive MST, which is an emulation of the mastering version of the original hardware version. He boosts at 16kHz for air, using the Shelf setting, with the bandwidth (aka "Q") set just a little below the middle position. He also sets a very slight boost at 33Hz, in the lower part of the frequency range.
Then he compares the bypassed and unbypassed versions and makes a couple of minor tweaks. He lowers the high-bell filter of the Massive Passive a little, and drops the boost on the Oxford EQ's high-shelving filter to 1.25 to 1dB.
WIDTH OF THE BAND
What are the takeaways from what Guzauski did with his master-bus EQ? One is that subtlety is the name of the game when EQing a full mix. His boosts are all in the 1dB neighborhood. If your mix requires boosts or cuts above about 2dB, most likely you're better off working on the EQ of the individual tracks instead.
Typically, engineers use the master bus to add some air on top (which is what Guzuaski was doing with the shelving EQ), or to provide an overall bass boost, or to apply the sonic attributes of a particular EQ to the full mix. The latter was one of the key reasons Guzauski chose the Manley Massive Passive, which has a signature sound, thanks to its passive circuitry and tube amplification stage.
Guzauski chose the UAD version of the Manley Massive Passive, in part to imbue the mix with its sweet tone.
Like with master bus limiting, you want to be particularly careful not to use a heavy hand with master bus EQ, particularly if your mix is going to get professionally mastered. If you're just aiming for overall clarity or punchy bottom end, it's probably better to leave that for the mastering engineer. However, if you're trying to give your mix a particular "sound," and what you’re doing is more creative than corrective, go for it.
PEAKY, PEAKY
Guzauski used a combination of shelving and peaking EQs to get his results. A peaking EQ features a filter that boosts or cuts a particular frequency and falls off in a bell shape to either side of the selected frequency (aka the "corner frequency"). How wide that bell shape is depends on the Q setting.
The lower the Q, the wider the bell, and vice-versa. A really high Q setting gives you an ultra-narrow bandwidth, allowing you to get surgical on small frequency ranges. With a bell filter set to a wider bandwidth (lower Q), you will be boosting or cutting in a broader frequency range on either side of the selected (aka "corner") frequency.
A shelving EQ applies the same boost or cut to one side of the selected ("cutoff") frequency. If it's a high-shelving filter it will affect everything above that frequency, and if it's a low-shelving filter, everything below it.
It may sound like all filters of a specific type (e.g. shelving) are identical, but they're not always. For example, you'll find plenty of subtle variations between shelving filters on different plug-ins. Sometimes you'll find differences on the same plug-in, for example, on the Waves H-EQ , you can choose from seven different varieties of bell filters and seven shelving filters.
The Waves H-EQ offers multiple variations within each filter type, each with a slightly different response. Here shown with a high-shelving filter.
The other type of filters you commonly find in EQ plug-ins are of the band-pass variety: high-pass and low-pass. These roll off from the cutoff frequency at slopes of varying steepness. Typically, the most gentle is 6dB per octave, and they get steeper in increments of 6dB from there.
Their names are somewhat counterintuitive because a high-pass filter cuts lows and a low-pass filter cuts highs. To add to the confusion, a high-pass filter is also known as a low-cut filter, and a low-pass filter is also known as a high-cut filter. The key to remembering which is which is the word "pass." High-pass filters let frequencies above the cutoff pass through, and low-pass filters allow frequencies below the cutoff to pass through.
A high-pass filter on the left, a bell filter in the center and high-shelving filter on this MOTU Masterworks EQ.
High-pass filters are not just used in mixing. You also find them in many condenser microphones, where they can be switched in to keep the mic from capturing too much room tone and other low-frequency information.
Low-pass filters, which roll-off highs above the cutoff frequency, can be used to get rid of unwanted high-frequency information on sources that are in the lower-mid and low-frequency ranges, and also to make a source sound further back in a mix. Because our ears perceive more high end in sounds that occur close to us, removing highs with a filter can help you move something back in a mix.
THIS TOO SHALL PASS
Many mixers use high-pass filtering to get rid of frequencies below the useable range of instruments or vocals, and thus reduce the muddiness of the mix. One way to go about that is to solo a track, play it back, and slowly turn up the cutoff frequency on the high-pass filter until you hear it start to thin out, and then back it off to just before that point. That way, you're getting rid of information you don't need but not cutting any important frequencies.
That said, there might be some instruments, for example, electric rhythm guitars, where you might want to go past that point where it audibly thins out. The lower frequencies in the guitar may not be needed and may just be cluttering things up. Listen both soloed and in context of the mix before deciding.
Example 1: In this example, you first hear a section of a mix with no high-pass filtering.
Example 2: Here's the same example with high-pass filtering applied as described above. Listen to the lower midrange, and you'll hear that it's a little cleaner there.
Example 3: This shows how you can use a low-pass filter to move something back in a mix. You'll hear the same mix as an example 1, but when it repeats, the rhythm guitars were low-passed at about 3.5 kHz, which makes them feel further back in the mix.