You’ll encounter several kinds of EQs in both hardware or software environments so it’s important to understand the various EQ types and which is best suited to address whatever miserable mistake you’re trying to fix, mix-wise.
Shelving. Applies equal gain change for all frequencies above/below a certain frequency. These can be useful for general shaping — adding brightness or beef to a sound.
Lowpass/highpass. With lowpass EQ, frequencies above a certain point, commonly referred to as the cutoff frequency, are attenuated while frequencies below the cutoff pass through unimpeded, hence the name “lowpass.” Likewise, highpass EQ attenuates frequencies below the cutoff, allowing frequencies above it to pass through untouched.
The rate at which frequencies are attenuated is called the slope, and is represented as a ratio (e.g.,12dB/octave). (See Figure 1).
Peak. The peak EQ boosts frequencies at, and around, the center frequency. This type of EQ allows you to accentuate or emphasize a limited slice of the frequency spectrum without dramatically affecting the general tonal quality. Often, you can control how wide or narrow the “slice” is (called bandwidth), for broader or more focused changes. (See Figure 2.)
Notch. Similarly, notch EQ is used to “notch out” or cut a narrow band of frequencies. Use this to reduce computer noise, ground hum, and so on. It can also help get rid of ringing drum tones, or take the “point” off electric guitars, snares, and other piercing mid-frequency sources.
In most DAWs, peak and notch EQs are often combined as one type, giving you the choice of cutting or boosting from one EQ.
Parametric. Parametrics are so called because they offer parameters for adjusting the EQ’s frequency, bandwidth, and gain. Most DAWs combine several EQ types into one “multi-band” parametric EQ (e.g., 4-band, 5-band, and so forth), where you can choose the type (lowpass, peak/notch, high-shelf) for each band.
Fixing Common Mix Problems
The combination of tracks and the way they interact can cause frequency ranges to build up, resulting in a dull or uneven mix (e.g., too boomy). Additionally, some tracks may “jump out” at certain frequencies.
A well-balanced mix where no single instrument or frequency range consumes too much sonic space may require a fair amount of nipping and tucking. Often, individual tracks need to be massaged to blend better with others, which requires close scrutiny to hear problem areas. To zero-in on these offending frequencies, it helps to use a peak EQ with considerable gain (10dB or more) and sweep this across the frequency spectrum. You won’t use this EQ in the final mix, but as you sweep the center frequency, you’ll be able to hear which frequencies help define the track’s tone, and which ones are problematic.
Experiment with this to find the “center” of various instruments — it’s an exercise that will pay off big when you run up against mixes that are:
Possible cause: Build-up of low and low-mid information as a result of the proximity effect from cardioid mics, too many tracks with extended low-frequency material, or poor room acoustics.
Solution: Highpass EQ on any track that isn’t supposed to sit in the low frequency range (percussion, vocals, guitars, strings) to make room for bass guitar and kick drum. Start somewhere between 100–200Hz, with a semi-steep slope. You can sometimes get away with a higher center frequency, provided you use a more gentle slope, which will make the EQ less obvious, but still clear out space in the low end.
Possible cause: Similar-sounding instruments competing for space in the midrange.
Solution: Separate similar tracks by using peak EQs to emphasize different frequencies, while cutting others, so that sounds complement and fill in around each other. On double-tracked guitars, for example, try boosting one at around 1.5kHz, cutting at 600Hz, and rolling off some of the highs starting at 3kHz. Conversely, reduce the other track by 2–3dB around 1–1.5kHz, and use a high-shelving EQ starting at around 3–4kHz to bring out more of its highs. This will allow both tracks more space, and create a better blend.
Possible cause: Midrange-heavy tracks masking and crowding high-frequency material (strummed, driving acoustic guitars, tambourines and shakers, vocals).
Solution: Apply lowpass starting around 5–6kHz on tracks that don’t need to “sparkle,” making space for high-frequency tracks to shine. Additionally, if mid-frequency tracks are still getting in the way, you can try cutting around 1–2kHz. You can also use shelving EQ (1–2dB of gain) to brighten similar tracks, such as grouped background vocals and guitars.
Possible cause: High frequencies being accentuated by one or more tracks.
Solution: Apply lowpass with a gentle slope to strident, overly bright tracks. If this isn’t enough, try making a slight dip in the 4–5kHz range.
Possible cause: Ringing drum tones; resonant frequencies from room acoustics picked up by the microphone, or from the instruments and vocalists themselves.
Solution: Notch EQ with narrow bandwidth to reduce or completely cut out unwanted frequencies.
During mixdown, EQ shouldn’t be limited to track-specific changes — feel free to make more “global” tonal changes, too. I often use EQ sparingly to treat the overall mix. I may use a little high-shelving starting at around 7–8kHz to add “air,” or cut out some of the low-mids with a gentle dip around 400Hz, which also helps to de-mud.
However, if you make radical EQ changes to an entire mix, it’s likely there’s something wrong on a micro level. Go back and solo each track, paying close attention to whether anything is adding too much bass or high frequency material, then adjust accordingly.
With practice, you’ll reach the point of quickly recognizing EQ-related problems, and how to fix them. Just remember to use your ears, not your eyes, and whenever possible, reference on several systems. This will help uncover any trouble spots, and ensure that your mix translates well to other playback systems. Your listeners will thank you for it.