How do I find resonant frequencies?

How do I find resonant frequencies?
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#1

I’ve seen a few tutorials on EQing. They mention one purpose is to remove resonant frequencies. They suggest to boost with a narrow Q and sweep. But to me everything sounds bad. Can anyone put into words what I’m supposed to be listening for?

Thanks in advance.


#2

Hi Damian, I think first we have to make a significant distinction in the interest of clarity…

EQing to remove a resonant frequency refers specifically to searching for an undesireable overtone that is already evident in the raw recording. For example, a rhythm guitar performance may have a constant ringing undampened open string enharmonic to the rest of the notes being played. As a result, it is distracting from an otherwise fine recorded performance and needs to be de-emphasised.

In other words, because you can ALREADY HEAR the ringing note, by boosting an eq with a narrow “Q” and sweeping through the frequencies, the aim is to get that tone (that you can already hear, although it may be somewhat masked by the surrounding audio) to “jump out”, at which point you can then turn it down, thereby minimising the negative effect of the resonant frequency.

The same principle and process can apply to virtually any sound… For example, a snare drum “boing” can be identified by the same process… But you already probably know that…As you’ve already observed, when boosting and sweeping with a narrow Q, EVERYTHING sounds weird…

The key to it is already being able to ALREADY HEAR the sound you want to get rid of BEFORE you start sweeping - thus my example above of the ringing open guitar string. I often find singing or humming the frequency that is annoying me to be helpful. Some mixers like to use a keyboard to help identify the specific note they are hearing.

Keep in mind that resonant frequencies often have overtones above and below the fundamental, so for example, if the problem is at 200hz, then the octaves above, at 400 & 800hz may be contributing to the problem.

However, as you have kind of implied in your question, not all reductive eq is done with the goal of finding resonant frequencies per se, and this is where it can get confusing watching mix tutorials, because some mixers don’t always specify the reasons why they are using eq…

In many cases, the use of reductive eq is just to more broadly de-emphasise freqency AREAS that mask other sounds, or are not needed in the context of the mix. To a greater or lesser extent, this may be an taste/artistic/stylistic decision.

In this case, the same principle applies - that you have to already have an idea of what you don’t like about the sound BEFORE you start sweeping around - but usually the sweeping can be done with wider “Q” settings. The sweeping method effectively becomes the audio equivalent of using a magnifying glass to find something that you know you have dropped.

As with anything in mixing, the first step is to LISTEN before doing anything. Only after first identifying the problem, then you can start using the tools at hand (in this case EQ) to solve the problem that you’ve already identified.

…and as with anything else in music, it takes time and practice to train our ears to hear and identify these things, so that is a BIG factor in the process,

I hope that answers your question - it’s actually quite a tricky thing to explain clearly!


#3

Yet you did so pretty much perfectly! Well done Andrew.


#4

+1

+1 again

Before I knew the frequency spectrum as well as I do now (which just comes with experience and awareness), I tried to associate a tonal timbres with nouns and verbs. Like thud, air, sparkle, crunch, warmth, boxy, muff…then eventually figure out stuff like (this is personal to me) definition/character/charm in a vocal is around 8k. Air is 12k. Boomy thump and thud in an acoustic guitar is usually somewhere below 500hz.

There are two basic questions I’ll ask before reaching for an eq (though the process is instinct by now).

  1. What is the problem? What do I WANT to hear that I’m not hearing now
  2. What is the cause? Is this a function of levels, compression, EQ…sometimes you won’t know…you’ll have to fish, you’ll have to try and error. Through experience, you’ll learn not to reach for an EQ if a stereo widener or a sparse reverb is the correct tool.

But when you fix something, take a sec to think about why the chance you made had the desired affect. Sometime you don’t know. I don’t really understand how the Manley Vari-Mu works. It modifies its own circuit somehow based on the relationships of two other things you do to it…or something like that. If you can’t understand whats going on ‘under the hood’, I just turn frickin knobs (since I’m just a genius like that), but I do try and make note of the cause and effect.


#5

Thanks for the replies.

Great explanation.


#6

The method Andrew described in post #2 is the one most commonly used as far as I know. If you’re having difficulties, you could try the method I use.

  1. Use a spectrum analyser to identify any resonant frequencies.
  2. Nuke them with your favoured EQ. I use a graphic.

#7

I generally use the same sweeping method as described by Andrew to find resonant frequencies. But sometimes it’s not so clear. For instance: I have quite a nasal voice which I would like to make less prominent. As Andrew explained, I might be hearing an overtone while not being aware of the fundamental. In my case I think it’s hidden somewhere around the 1K region. Lately I’ve been using a bandpass filter to single out the fundamental from the overtones in combination with the usual sweeping method. I’m still not sure I’ve found the holy grail, but I feel I’m getting closer…
(any further tips are welcome!)

One more thing: this nasal effect on my vocal is worse in some parts than others. So once I’ve found the offending frequencies I use a dynamic Eq to attenuate. The free TDR Nova plugin is excelent for this job. The method also works well on sibilants.

While posting I just found out the last post is a year old… Oh well, maybe someone will read it anyway.


#8

Great answer there. Couldn’t have said it better myself.