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So mixing... (audio engineering). When using an equalizer on trackouts/instrument tracks, the general approach is cut out the "bad frequencies" and increase the "good frequencies" to accentuate the instrument track.

What exactly are the bad frequencies? I can sweep across the audio spectrum and a lot of frequencies can sound "bad", so what exactly should I be cutting specifically and to what degree of decibels?

At the same token, what are the good frequencies, how wide should my Q be when accentuating them and to what degree of decibels?

  • They're not bad frequencies. They are conflicting. An example would be acoustic guitar. Some are more trebly, some more bassy. But you don't have a dozen acoustics in the studio so if you want it to sound brighter so it stands out more you could EQ it. Maybe the snare you have doesn't sound 'tight' as you'd like for this particular song ... eq it to make it sound like a different snare. Does doing that make the snare bad? – Randy Zeitman Oct 4 at 4:28
  • What is "Q" in this context? Q factor? A measure of the bandwidth of the bandpass filters in the equalizer? Or something else? – Peter Mortensen Oct 4 at 17:49
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There is no one way to use an EQ, but there are a few common techniques that people use to EQ, and they can be applied on most sources.

First a few general tips:

  • Make small changes. EQs are not magic, and they will not instantly improve your recording. They are best for making small tweaks.
  • Be careful with boosting. It's oftentimes better to attenuate first and then increase the overall gain if necessary.
  • Try things. Try whatever you want, and learn from it. If you want something to sound in a specific way, that's completely fine. Don't let random people on the Internet tell you what to do 😉

Now, the techniques:


Cutting / Filtering

You may have heard about something like a high-pass or low-cut filter. This concept can be achieved by taking a EQ band and positioning it to "cut" only the lowest frequencies.

If you are recording a violin for example, their lowest string G is just around 190 Hz. Any information below 190 Hz is likely not useful, so you can simply cut it out. If you repeat the same concept on every instrument in the mix, you'll likely increase the total clarity.

High-Pass/Lo Cut Filter

You can of course do the inverse to achieve a low-pass filter, but this is not as common (especially not with acoustic instruments) as it results in more of an effect.


Cleaning

You mention the "bad" frequencies. What you are referring to are frequencies that are especially resonant, compared to the rest of the spectrum. The reason the "bad" frequencies occur can be due to the room they were recorded in, the instrument itself, the playing technique, or a number of other reasons.

The act of removing (attenuating) these frequencies is commonly referred to as cleaning.

  1. Pick the most narrow Q your EQ will allow, max out the gain and scan through the spectrum until you find especially resonant frequencies.

    Scanning the spectrum

  2. Once you find the most resonant ones, widen your Q and attenuate the problematic frequency and its near range with your gain set to something like -1 to -3 dB.

    Attenuating frequencies

Note that the resonant frequencies will probably reoccur one octave above the last, so it can be useful to start in the low range, and then go up by octaves (double the frequency) using a lower gain each time


As for specific values, I gave you a general idea of some of it, but really as I said in the beginning, there are no one-size-fits-all solution in EQing. Play around with different values and see what happens. The most important tool at the end of the day, is your ears.

If it sounds good, it's good.

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    Check out this bad boy: audio-issues.com/music-mixing/… – schadjo Oct 3 at 15:30
  • “Pick the most narrow Q your EQ will allow” – too narrow is usually not good for the finding-step, unless it's something like a static hum you want to remove. A width of ½ to 1 octave is generally good. If you make the peak too narrow, then it'll make a bad ringing sound everywhere, which may actually be what the OP's problem was when trying the sweeping. – leftaroundabout Oct 3 at 16:56
  • @leftaroundabout never had that problem myself but it's certainly good to know that can be an issue, thanks. – Oscar Lundberg Oct 4 at 17:52
  • Re "most narrow Q" (two instances) and "widen your Q": Don't you mean "most narrow bandwidth (highest Q)" and "widen your bandwidth (lower Q)", respectively? (Ref. Relationship between Q and bandwidth) – Peter Mortensen Oct 4 at 17:59
  • @PeterMortensen Fair enough, but Q is quite unintuitive especially for beginners and that's why I phrase it as "most narrow Q". This phrasing along with the image examples makes it unlikely that it will be misunderstood. – Oscar Lundberg Oct 7 at 11:43
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The best way to use an equaliser is not to NEED to use it.

Yes, some instruments share a frequency range, playing them together can sound muddy. So DON'T play that pair of instruments together. It's called good orchestration, and it's been part of the composer's art for a thousand years.

You say "the general approach is cut out the "bad frequencies" and increase the "good frequencies" to accentuate the instrument track". No. If you're GOING to eq, most of the time you should cut. Maybe a gentle boost in the 'presence' or 'air' ranges of a vocal. But generally beware of boosting, particularly of boosting a narrow range.

You might want to cut the low bass, below the range that the anticipated playback system can handle. Leave it in for the 'club mix' though - but I hope you've got monitors that can tell you what you're getting!

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    Exactly. Narrow boosts are good for a wah-wah sound, else... not so much. – leftaroundabout Oct 3 at 16:57
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    There are three fundamentally different use cases for EQing. One is to literally "equalize", i.e. (mostly) remove unnaturally overemphasized frequencies and (rarely) boost missing ones to make it sound more "natural". The second case is sound design, i.e. make it sound "less natural". For example, a heavy metal kick drum needs to be aggressively EQd in a specific way until it sounds nothing like an actual kick drum anymore. However, that is the sound a kick drum in this genre is supposed to have. Number three is "cleaning up the mix". With a good arrangement, this shouldn't be needed. – Jörg W Mittag Oct 3 at 23:20
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The use of EQ is twofold:

  1. to try to give each instrument/part it's own space in the spectrum.

First up - think about what the objective is of a good mix? You want to hear each part that contributes to the musical arrangement, clearly and in it's own space. Of course, you can't do any better than the raw material that you have recorded here! So already part of mixing is thinking about the arrangement. (Years ago, most recording sessions had a specialist arranger - these days arranging and mixing tend to overlap a lot.)

So each musical part (this could be bass, drums, percussion, lead vocal, backing vocals, horns, strings, guitars, keys ... whatever) wants to sit in its own space and be clearly audible. If the arrangement is good this should mostly look after itself but EQ can help. Here are some typical uses:

  • male lead vocals often get a little boost at around 3-5kHz - known as presence, this helps it "cut through". Other parts that might interfere might get a slight cut at the same frequency.

  • bass can sound better (especially on smaller speakers) when boosted a bit at around 200-250Hz. This gives a bit of "pop" to the sound.

  • cymbals might be boosted a bit at around 5-10kHz and up.

and so on. The key here is not to overdo it. Less is more.

  1. To remove any annoying frequencies, or just stuff that shouldn't be there. For instance:

    • many parts will get a "low cut" at around 125Hz (analogue mixers usually have a dedicated switch for this). This is to remove any low end "rumble" which might not be directly audible but still decreases headroom, and keep the bass end of the mix clean.

    • a vocal or other part that has some annoying "ring" to the sound - you can use EQ to tune into that part of the spectrum and reduce it.

Basically you use your ears. just beware of overdoing it! On today's DAWs which have almost unlimited EQ and FX, it is all too easy to go overboard, and end up with a mix that sounds really unnatural and awful. The best approach is to try to start with good musical performances well recorded, and then only use EQ to fix what really needs fixing.

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What exactly are the bad frequencies? I can sweep across the audio spectrum and a lot of frequencies can sound "bad", so what exactly should I be cutting specifically and to what degree of decibels?

There's no general answer to this: it depends on the instrument, the recording system and the room. You want to avoid resonances, where one frequency sounds much louder than the rest because the room acts to amplify this frequency.

At the same token, what are the good frequencies, how wide should my Q be when accentuating them and to what degree of decibels?

Accentuation quickly leads to listening fatigue. Your goal is to make the recording as good a match as possible for a live session in a perfect room.

There's a pitfall here: when you listen to the recording in your studio via loudspeakers, your playback chain includes the loudspeakers and the room they're in. This adds its own coloration, which you may have to compensate for by running an EQ in the playback chain, separate from any EQ that's applied to the recorded tracks.

When you record a live concert, things get more complicated: you need one EQ for the PA system (which is geared to avoiding feedback), and a separate EQ for the recording.

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If you know the key of the song, you can use one of those frequency/keyboard graphs to find the fundamental frequencies for your track. Most people use their ears to do this but its nice to cheat sometimes. For example, my song is in the key of A major and I know A is 440hz. Based on that I know where the A frequencies exist within the frequency range like: 110hz, 220hz, 880hz, 1760hz... etc. Just multiply by two. When you do this you are only focusing on the root note so you can try EQing other frequencies/notes on the key you're working on. I found this very useful when I started doing it, also there are charts with frequency ranges for every instrument that explains what happen when you boost within that range. Fun Stuff.

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    I find this a very dubious approach. Most engineers do not consider EQing a musical effect that should have anything to do with the key or the specific notes played by the instruments (except for resonances that are only triggered by one particular note or partial). – leftaroundabout Oct 3 at 17:12
  • It's clearly unconventional, but, hey, making music is supposed to create new stuff. And if it sounds good, it is good. It needs to be said that this isn't the typical way of using an EQ, though. OP probably asked rather for the typical use case and how to do that. – Alfe Oct 4 at 9:37

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