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Author Topic: Harmonics when ringing out  (Read 3144 times)

dawsonbristol

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Harmonics when ringing out
« on: December 30, 2023, 11:15:52 PM »

I feel like I need to preface this with the fact that obviously I understand that often if (for example) 1k rings, 500 or 2k might be an issue as well. Question: I’ve heard it posited recently that, when you’re ringing out, if you just duck frequencies as they appear, sometimes you’ll be cutting high harmonics of lower frequencies. Specifically the argument someone made was that you should focus on cutting what’s “lower” regardless of the order of priority, like if you’re messing around with feedback above 5k you’re chasing your tail should be addressing something lower.

What I do not understand is if/why a harmonic would ever ring before its own fundamental when you’re just slowly boosting level. Even if the answer is “that’s just how it is with systems sometimes” I just wanna know because it’ll affect my workflow

In addition, does cutting the fundamental actually impact the level of its harmonics? Eg when 500 and 1k are taking off would a cut at 500 make 1k less prominent too? Haven’t had a chance to test for myself, need bigger brains than mine to opine
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John Roberts {JR}

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Re: Harmonics when ringing out
« Reply #1 on: December 31, 2023, 12:25:49 AM »

Feedback modes are generally related to loudest frequency response.  I don't recall seeing harmonic pitch relationships between modes. 

[edit- TMI, years ago I speculated about detecting the delay in the feedback path and introducing an opposite polarity signal, effectively subtracting that source of feedback from the mic feed. In theory this seemed promising, but the response of feedback paths are not very flat. At the time cheap high quality delay was not trivial so I abandoned this /edit] 

JR
« Last Edit: January 01, 2024, 09:01:41 AM by John Roberts {JR} »
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Steve-White

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Re: Harmonics when ringing out
« Reply #2 on: December 31, 2023, 01:40:37 AM »

Let me add some food for thought with regard to the harmonics which are typically above the fundamental.

Good monitors make for easier setup.

If the source isn't fairly flat, the feedback points can be all over the place.

With good monitors, I pull the first feedback frequency out the most and less and less (2-3db) on subsequent frequencies which are typically harmonics of the fundamental.

Reflections can also come into play as can mechanical feedback of the floor vibrating and resonating.  Low metallic ceilings can also be a problem.  As well, proximity.  I do the initial ring-out with empty stage then have an assistant walk up to the vocal mics for a final check and tweaks. 
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Ivan Beaver

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Re: Harmonics when ringing out
« Reply #3 on: December 31, 2023, 05:17:04 PM »

Forget about the "harmonics".

They will still be there, with the same relationship to the fundamental.

It is the loudest thing at the mic position that will start to feedback.

I have only been in this business about 4 decades, and never once thought about (or heard about) a harmonic relaionship in regards to feedback.

If you pull the fundamental freq down (via eq or physical position of mic and or speakers and or reflections (think cowboy hats) the harmonics will come down.

Also with feedback, any harmonics that are generated are typically distortion components,  This is because feedback is fundamentally a sine wave oscillation, that is based on the overall gain.

look up (and run through a couple of different numbers entered) PAG-NAG equations to get a better idea of what affects gain before feedback the most.  Hint, it is the distance between the mic and the source.  But playing with the numbers helps to give you an idea of how much certain things matter, and how little other things matter
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Scott Holtzman

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Re: Harmonics when ringing out
« Reply #4 on: January 01, 2024, 01:55:34 AM »

Forget about the "harmonics".

They will still be there, with the same relationship to the fundamental.

It is the loudest thing at the mic position that will start to feedback.

I have only been in this business about 4 decades, and never once thought about (or heard about) a harmonic relaionship in regards to feedback.

If you pull the fundamental freq down (via eq or physical position of mic and or speakers and or reflections (think cowboy hats) the harmonics will come down.

Also with feedback, any harmonics that are generated are typically distortion components,  This is because feedback is fundamentally a sine wave oscillation, that is based on the overall gain.

look up (and run through a couple of different numbers entered) PAG-NAG equations to get a better idea of what affects gain before feedback the most.  Hint, it is the distance between the mic and the source.  But playing with the numbers helps to give you an idea of how much certain things matter, and how little other things matter


Your monitor should have more than enough output, if it doesn't get a bigger one.  My guess is you are trying to get to much out of it if you are chasing the birdies (second round of feedback frequencies).  Knock down the main offenders and call it a day.


Once you get good at it you should be able to walk up to the monitor.  Create a little feedback, knock down that frequency (you should be able to do this without a spectrum analyzer) then repeat, maybe with a few mechanical taps on your thigh.  If you are wringing out those last few DB you are wasting time. 
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Art Welter

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Re: frequency peaks when ringing out
« Reply #5 on: January 01, 2024, 04:59:57 PM »

Specifically the argument someone made was that you should focus on cutting what’s “lower” regardless of the order of priority, like if you’re messing around with feedback above 5k you’re chasing your tail should be addressing something lower.

What I do not understand is if/why a harmonic would ever ring before its own fundamental when you’re just slowly boosting level.
If you are slowly increasing level and that level is reflected back into the mic by a hand, face, hat or  glasses in front of the mic, the built in +3 to +6dB high frequency "presence peaks" in typical vocal mics may "take off".
Since the presence peaks are often centered around 5-10kHz, even a "flat response" speaker may need to be cut in those regions.

At the lower end of the spectrum, the mic may not feed back, but the +5-15dB proximity effect boost when the mic is close to the sound source may require a corresponding cut to counteract that rise, without it the mic may sound "muddy".
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Ivan Beaver

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Re: Harmonics when ringing out
« Reply #6 on: January 02, 2024, 08:09:23 AM »


Your monitor should have more than enough output, if it doesn't get a bigger one.  My guess is you are trying to get to much out of it if you are chasing the birdies (second round of feedback frequencies).  Knock down the main offenders and call it a day.


Once you get good at it you should be able to walk up to the monitor.  Create a little feedback, knock down that frequency (you should be able to do this without a spectrum analyzer) then repeat, maybe with a few mechanical taps on your thigh.  If you are wringing out those last few DB you are wasting time.
Exactly.

Once you knock down the first couple (say 2 or 3 major problems) the rest is an exercise in futility.  If you keep whacking away, you will destroy the tonal character.
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Noah D Mitchell

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Re: Harmonics when ringing out
« Reply #7 on: January 02, 2024, 08:57:13 AM »

Exactly.

Once you knock down the first couple (say 2 or 3 major problems) the rest is an exercise in futility.  If you keep whacking away, you will destroy the tonal character.


Do these same guidelines apply when eq’ing an individual channel, like a lapel mic? Or primarily just mix masters and monitor busses?
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Steve-White

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Re: Harmonics when ringing out
« Reply #8 on: January 02, 2024, 04:07:38 PM »


A) Do these same guidelines apply when eq’ing an individual channel, like a lapel mic? B) Or, primarily just mix masters and monitor busses?

A) Yes

B) Everything
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Russell Ault

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Re: Harmonics when ringing out
« Reply #9 on: January 02, 2024, 07:23:11 PM »

Do these same guidelines apply when eq’ing an individual channel, like a lapel mic? {...}

Not to steal Ivan's thunder, but I would suggest that the answer to this question is "It Depends™". I agree with everything Ivan said, but for any given application you have to ask yourself how important "the tonal character" of the sound actually is; for example, in speech-oriented applications the answer is often something along the lines of "do whatever you need to do to make the words intelligible and the system feedback-stable, and if after all that it still sounds even vaguely like a human voice then you can call that a win".

-Russ
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Re: Harmonics when ringing out
« Reply #9 on: January 02, 2024, 07:23:11 PM »


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