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Old 5th April 2018
  #121
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Wyllys's Avatar
 

Quote:
Originally Posted by shufflebeat View Post
AntG, that change of tack is as close as we're going to get to "ok, you were right".

Also, you can be damn sure once the insults start flying SamC has run out of answers. The questions were straightforward enough.

Sam, for a man who does sound for more than 200 gigs a year you're not the best listener. If you'd bothered trying to understand the problem you could have saved us all 2+ pages of arrogant BS.
What color is the sky in your world? I'm sorry if you aren't getting the help you need here. We're audio professionals, not psychiatrists.

Last edited by Wyllys; 5th April 2018 at 08:16 PM..
Old 6th April 2018
  #122
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Quote:
Originally Posted by Samc View Post
I'm thinking that we should include reduced hearing and incompetence to the list of what cause feedback...they're both certainly more valid than "cheap preamps" in my opinion.
I never claimed that cheap preamps were the only reason for feedback. What's I'm saying is that a cheap preamp is much more likely to go microphonic at maximum gain than a quality preamp will.

I am going to run some experiments yet for the last few day's I've been out at the time of day when it would be OK to experiment.
Old 6th April 2018
  #123
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I was thinking about this argument earlier today and came up with a great analogy.
Its an analogy and not perfect but here goes.

I'm equating it to driving a car around a corner as fast as possible without losing control and spearing off the corner. The fastest speed you can drive is the maximum gain before feedback and feedback is flying off the road.

Speaker placement and microphone type/quality/location defines the corner. Any changes here change the corner and the possible speed it can be taken at. What the driver has at his control is gain staging and eq and we aren't talking about the eq yet.

Now, what I said to start the flamefest here was equivalent to saying that a driver with better technique can go around the corner faster than a driver with poor technique. Going fast into a corner, tugging on the steering wheel and lifting off the throttle is going to have you spearing off the corner (feedback) while a driver with more skill is going to keep the car on the road.

Now Wyllys and Samc have come along and said that this was nonsense. They stated that no matter how good or bad your driving was (gain staging) the car was going to go around the corner at the same maximum speed. I came back and said that, "sure, if your driving a Ford Focus RS (high end gear) then yes you can go around the corner faster than if your driving a VW Beetle (low end gear) but they came back again and said that this was nonsense.

Their statement was effectively that "Stig" driving a Ford Focus RS couldn't corner faster than a numbskull driving a 1975 Beetle.

OK, its an analogy but you can see that some of us are incredulous at this.

Now this is the real problem here. All I really said was that practicing good technique would deliver better results (higher gain before feedback) and then I had Wyllys and Samc jumping on me telling me that I was leading people astray and giving bad advice.

Several of us were perplexed and much of this was to do with Wyllys and Samc's attitude.
Now Wyllys and Samc may well be correct. They well could be correct but their attitude still leaves me perplexed.

If they had said something along the lines of, well you know, that's what I was taught when I was starting out but now we know its not true then I might have paid them more heed. The trouble is that they took a derisive and confrontation attitude instead which has left me an some others perplexed and incredulous.

Have I given away some secrets of the business that I'm not supposed to reveal and the guys are trying to shut it down? Is the whole point that they want people to do a bad job so that they are more likely to get hired? (OK, this IS a conspiracy theory).

Do they just like being Jerks (more likely) and lording it over people?

Either way I'm still going to gain stage my mixer correctly and run some experiments.

Last edited by AnthonyG; 6th April 2018 at 02:37 PM..
Old 6th April 2018
  #124
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Wyllys's Avatar
 

Quote:
Originally Posted by AnthonyG View Post
I never claimed that cheap preamps were the only reason for feedback. What's I'm saying is that a cheap preamp is much more likely to go microphonic at maximum gain than a quality preamp will.

I am going to run some experiments yet for the last few day's I've been out at the time of day when it would be OK to experiment.
You say that preamps go microphonic when turned up full. In the nearly 60 years I've been working with audio gear I cannot remember that happening, but...

If you want to test your theory you can simply turn the preamp up full, take a pencil and tap the gain knob. If it's "microphonic" you'll hear the tapping clearly.
If you hear the tapping, get it repaired or replace it.
Old 6th April 2018
  #125
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Quote:
Originally Posted by AnthonyG View Post
I was thinking about this argument earlier today and came up with a great analogy.
Its an analogy and not perfect but here goes.

I'm equating it to driving a car around a corner as fast as possible without losing control and spearing off the corner. The fastest speed you can drive is the maximum gain before feedback and feedback is flying off the road.

Speaker placement and microphone type/quality/location defines the corner. Any changes here change the corner and the possible speed it can be taken at. What the driver has at his control is gain staging and eq and we aren't talking about the eq yet.

Now, what I said to start the flamefest here was equivalent to saying that a driver with better technique can go around the corner faster than a driver with poor technique. Going fast into a corner, tugging on the steering wheel and lifting off the throttle is going to have you spearing off the corner (feedback) while a driver with more skill is going to keep the car on the road.

Now Wyllys and Samc have come along and said that this was nonsense. They stated that no matter how good or bad your driving was (gain staging) the car was going to go around the corner at the same maximum speed. I came back and said that, "sure, if your driving a Ford Focus RS (high end gear) then yes you can go around the corner faster than if your driving a VW Beetle (low end gear) but they came back again and said that this was nonsense.

Their statement was effectively that "Stig" driving a Ford Focus RS couldn't corner faster than a numbskull driving a 1975 Beetle.

OK, its an analogy but you can see that some of us are incredulous at this.

Now this is the real problem here. All I really said was that practicing good technique would deliver better results (higher gain before feedback) and then I had Wyllys and Samc jumping on me telling me that I was leading people astray and giving bad advice.

Several of us were perplexed and much of this was to do with Wyllys and Samc's attitude.
Now Wyllys and Samc may well be correct. They well could be correct but their attitude still leaves me perplexed.

If they had said something along the lines of, well you know, that's what I was taught when I was starting out but now we know its not true then I might have paid them more heed. The trouble is that they took a derisive and confrontation attitude instead which has left me an some others perplexed and incredulous.

Have I given away some secrets of the business that I'm not supposed to reveal and the guys are trying to shut it down? Is the whole point that they want people to do a bad job so that they are more likely to get hired? (OK, this IS a conspiracy theory).

Do they just like being Jerks (more likely) and lording it over people?

Either way I'm still going to gain stage my mixer correctly and run some experiments.
This is an untrue and misleading recount of what happened, your made claims that are FALSE and we/I said so and even posted up an article which explains the facts and you keep repeating the same falsehoods over and over. In fact, your claim about cheap mic preamps is so wrong that no one else has supported it.

Instead of trying to learn from the thread you’re using it to scapegoat and cuss us out...misrepresenting the facts in the process, so petty and sad.

Your claims are FALSE and your analogy is also false!!!

Last edited by Samc; 6th April 2018 at 05:04 PM..
Old 6th April 2018
  #126
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I just finished soundcheck and just for ****s and giggles decided to do some tests...with the position of the mic and monitors fixed, feedback happens at the same SPL all the time. Mic pre slammed to distortion, not slammed, stereo bus slammed and distorted, the onset of feedback was always the same thing didn’t happen sooner or later one way or the other.

But...maybe this is a trick to steal work from you so don’t take my word for it go test it yourself.

We have already stated the importance of good gain-staging, that goes without saying....but improper gain-staging does NOT cause feedback as was claimed. In the next few days I’ll test a little Yamaha mixer next to an XL4 to debunk the other ‘theory’.
Old 6th April 2018
  #127
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Wyllys's Avatar
 

I was going to pass on this, but a sudden drop in temperature and high winds have me holed up inside.

Quote:
Originally Posted by AnthonyG View Post
I was thinking about this argument earlier today and came up with a great analogy.
Its an analogy and not perfect but here goes.

I'm equating it to driving a car around a corner as fast as possible without losing control and spearing off the corner. The fastest speed you can drive is the maximum gain before feedback and feedback is flying off the road.
I can't agree that flying off the road is analogous to feedback, but rather exceeding system limitations to the point of physical damage. To be analogous, you'd have to be able to get back on the road again by merely reducing your speed...and that ain't gonna happen once you've crashed.

But if it helps you to use an analogy, I'll oblige.

For an analogy to be valid, all terms must be equal...or ANALOGOUS. To create an analogy between running an audio system and driving a car, everything must correspond in function, requiring a working knowledge of BOTH systems
in order to compare (substitute) apples : apples.

Thus:

feedback threshhold : speed limit

Both are set by law, the first by physics, the second by government.

system gain : speed

curve in the road : compression

rough road : distortion

jalopy : cheap, low quality gear

Lamborghini : Samc level system

(I drive a Jetta TDI Sportwagen.)

and so on.

Exceed the limit in either terms and you get audio feedback...which in highway terms is the sound of the siren on the squad. Curves (compression)? Well, they'd amplify the effect of speed requiring a reduction for continued safe operation. The analog would be reduction in headroom.

I hope that helps. If you have any questions regarding other aspects/components in the analogy, do please ask.
I'm a really good driver. 60 years and no accidents...but I have gotten a couple of speeding tickets...

Quote:
Now Wyllys and Samc may well be correct.
I should hope so! And remember...

Those sheep in the pasture by the side of the road aren't groupies.

Last edited by Wyllys; 7th April 2018 at 03:17 AM..
Old 6th April 2018
  #128
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Quote:
Originally Posted by Samc View Post
A compressor will bring up low level noise and increase the RMS level of the signal effectively making it louder.
Also, if you've gained up the monitor to compensate for the compression, compressors inevitably RELEASE once the signal drops below the threshold. Now, you've got what amounts to a gained up monitor.
Old 7th April 2018
  #129
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Quote:
Originally Posted by blue439 View Post
Also, if you've gained up the monitor to compensate for the compression, compressors inevitably RELEASE once the signal drops below the threshold. Now, you've got what amounts to a gained up monitor.
Yes, but you need to have a good working knowledge of the compressor to know these things.
Old 8th April 2018
  #130
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Quote:
Originally Posted by blue439 View Post
Also, if you've gained up the monitor to compensate for the compression, compressors inevitably RELEASE once the signal drops below the threshold. Now, you've got what amounts to a gained up monitor.
Absolutely, yes, yes, yes. I couldn't have put it better myself.

I did try in #114 but W&S seem determined to disregard what is as plain and clear to anyone who has ever experimented with a compressor in even the most basic setup.

Cheers, blue.
Old 8th April 2018
  #131
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Quote:
Originally Posted by Samc View Post
I just finished soundcheck and just for ****s and giggles decided to do some tests...with the position of the mic and monitors fixed, feedback happens at the same SPL all the time. Mic pre slammed to distortion, not slammed, stereo bus slammed and distorted, the onset of feedback was always the same thing didn’t happen sooner or later one way or the other.

But...maybe this is a trick to steal work from you so don’t take my word for it go test it yourself.

We have already stated the importance of good gain-staging, that goes without saying....but improper gain-staging does NOT cause feedback as was claimed. In the next few days I’ll test a little Yamaha mixer next to an XL4 to debunk the other ‘theory’.
No-one in this thread has ever suggested that the usual rules don't apply.

For the benefit of the hard of hearing - a system will feed back in accordance with the circumstances laid out clearly by W&S earlier in the thread.

Several of us have suggested that a restricted dynamic range, such as that resulting from inappropriate use of compression/limiting or the clipping of a signal from an overdriven input (i.e., a powered monitor) will encourage the unwary to raise the overall level rather than sort out the issue upstream. This will push this part of the system beyond the "loop" threshold and the system into feedback.

In order to reassure myself that I've not inadvertently strayed into a parallel universe, like Sam I too have set up a small system at home (weekend off) and illustrated the validity of this proposal beyond any possible doubt. I recommend you do the same.

What Sam suggests in the post I quote is absolutley true and no-one has suggested otherwise (don't take my word for it, read the thread if you have no further reason to live).

Sam seems to be experimenting with a system that does not include the variable sensitivity brought about be the compression/clipping variable which, and I must stress this most strongly, is the original and only point if the discussion.

Were Sam to compress the signal and raise what is normally referred to as the "make up" gain to compensate for the gain reduction (compression) he would find that the system would be more inclined to feed back.

This is not complicated or difficult, every sound engineer I know will consider this to be "page 1" stuff. It doesn't require extensive in depth knowledge of the mysteries of compression or a signed copy of Newton's birth certificate.

There are only two reasons I can think of why W&S are maintaining this charade:

1) they know of the existence of the rules they love to quote and refer to but don't actually understand or have a valid working mental model of what is involved (having followed these fora for some time I don't think this is the case).

2) they know that AntG's proposition, clumsily but humbly stated, was in fact correct - but having dismissed the idea out of hand with a large measure of condescension - now find it difficult to admit there was some merit in his suggestion, preferring to resort to smoke screens and insults to cover their embarrassment.

Unless anyone has anything constructive to add I'll be off.
Old 8th April 2018
  #132
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Least we forget, here are the original...not the remixed, restated and nudged version of events.

Quote:
Originally Posted by AnthonyG View Post
Getting your gain staging right to can help a lot. I find that having the preamp gain higher than it should be is inducive to creating feedback.
Distortion maybe, but not feedback.

Quote:
Originally Posted by AnthonyG View Post
Sure its everything. Maybe on high end systems with clean preamps the preamp isn't a problem yet on some lower end systems that I have used I find I can get more volume before feedback from not going to high with the preamp and turning up the power amp instead.
False...gain is gain and the system does not care which stage of the system you gain up from.

Quote:
Originally Posted by AnthonyG View Post
If you really crank up some cheap preamps they will start squealing on their own without much power amp volume.
I have NEVER witnessed or heard about this happening...never.

Quote:
Originally Posted by AnthonyG View Post
On high end systems it probably doesn't but then again anyone running a high end system will gain stage properly anyway.

If you take a cheap mixer and max out the preamp gain and only turn up the main sliders slightly then you should expect more feedback than if you gain staged the mixer properly.

That's my experience anyway.

EDIT. Well maybe your right and its a different issue. Maybe I'm talking about microphonics.
False again...gain is gain and the system does not care where you turn up or turn down. Overloading any stage will only add distortion; it does not increase the likelihood of feedback...and cheap mixers and preamps are NOT more likely to feedback than expensive mixers and preamps.

It should be noted that there have been no scientific arguments to support these claims. None of the made up scenarios presented thus far actually explain anything, they use a vague language to try and influence and present a picture that is at best irrelevant and misleading.

Not a single credible article/paper anywhere mentions gain-staging or the quality of the mixer/preamp in relation to feedback...NONE. None of the reference handbooks and not one article that I've seen on the internet thus far makes these claims or even mentions these things in their explanation of the cause of feedback.
Old 8th April 2018
  #133
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For the sake of clarity and gut honesty...

Quote:
Originally Posted by Wyllys View Post
Not overlooked. It's just that sometimes you have to reiterate the basics for thread readers when the discussion gets tangential or side-tracked with special case scenarios or "what-about-ism".
Quote:
Originally Posted by shufflebeat View Post
Accepted.

I accidentally wandered off at a tangent due to a misreading (old age) but Sam replied to my post after I'd realised but before I'd deleted it so I was obliged to clarify.

Will read closer on phone.
Here is the 'remix' a couple of pages later......
Quote:
Originally Posted by shufflebeat View Post
I tried to avoid this tangent by deleting a post which, admittedly, was off topic but Sam had replied in his usual condescending way but didn't seem able or willing to back up his assertion with answers to simple, real life questions.
Old 8th April 2018
  #134
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mintaka007's Avatar
From audiomasterclass.com. Take what you will out of it, there are some points here for all to marinate in. This is basic stuff, or so I thought, but it seems like it needs to be said:

Now the question is whether carefully balancing the gain and fader (of the same channel) will improve the situation regarding howlround.

Quick question... What does the gain control do?

Answer: It boosts the level of the signal.

Another question... What does the fader do?

Answer: It lowers the level of the signal.

Clearly both of these controls have an effect on the loop gain of the system and can therefore affect feedback.

But if you raise the gain by 6 dB, the output from the loudspeakers goes up by 6 dB (assuming no compression). If you then lower the fader by 6 dB, then the output goes down to what it was before.

In fact, however many decibels you change the gain, if you move the fader by an equal number of decibels but opposite in direction, then the output level and loop gain will stay the same.

So the short answer is that you won't improve anything however much you play about with the relative gain and level, assuming that you always use one to exactly compensate the other.

But there is a 'but'...

The exception is if you have your gain too high on the point of clipping. (If you do this you will almost certainly have your faders set very low to compensate.)

Distortion induced by clipping adds an uncertainty into the feedback equation by changing the balance of frequencies.

The result is not going to be good. In general, distortion adds energy to the higher frequencies. Howlround is always unpleasant but high frequency howlround can be ear splitting.

So set the gain correctly using the normal methods and concentrate on the factors that really can reduce howlround...

Firstly if you can get the microphone closer to the sound source, you can get a greater proportion of the sound source you want to pick up, in comparison to the sound coming from the speakers.

Secondly, as much as possible place the speakers so they don't fire sound directly at the microphone. And from the opposite point of view, position the microphone as carefully as you can so that it doesn't point at the loudspeakers.

There are more weapons in the anti-howlround arsenal, but these two are the biggest guns.
Old 8th April 2018
  #135
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mintaka007's Avatar
sooooo, what this means is that Samc is correct in that a 6db increase in gain and a 6db decrease in fader movement will net the same spl. Where sam is incorrect is this is only true if you are gain staged correctly. If you are introducing a gain level that is too hot, I.E. hanging out around or above 0 too much, then you can introduce the higher chance of feedback with the spl being the same by lowering the fader.
Old 8th April 2018
  #136
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mintaka007's Avatar
I am in the camp of soundguys that learned on analog boards and gain staged first, then introduced fader movement for volume. I have worked around guys that set faders to unity and then used gain to level the mix. Obviously you still need fader movement as the mixing progresses, I am just talking initial setup stuff.

Learning how to recognize the offending frequencies that are feeding back and adjusting eq to compensate if you need the volume is the way most common of eliminating feedback in smaller rooms. The main problem in smaller rooms is sometimes overcoming stage volume where you have musicians that for whatever reason refuse to turn down. Getting things like vocals and acoustic guitar over the guys with rockstar syndrome often requires riding the edge of feedback and eq creativity to attempt to solve the problems these overly loud players create.

If you could convince some of these loud players that the overall band sound and audience experience is much better if the volume is optimized to the room and system, then our jobs would be much easier. We can wish right?
Old 8th April 2018
  #137
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Quote:
Originally Posted by mintaka007 View Post
sooooo, what this means is that Samc is correct in that a 6db increase in gain and a 6db decrease in fader movement will net the same spl. Where sam is incorrect is this is only true if you are gain staged correctly. If you are introducing a gain level that is too hot, I.E. hanging out around or above 0 too much, then you can introduce the higher chance of feedback with the spl being the same by lowering the fader.
I'm not clear on what I said that is incorrect...as far as physics is concerned, gain is gain and the system does not care where it is increased or attenuated, incorrect gain staging at any point in the system will/does not change this fact. There is no circumstance where a you increase by a certain amount (to create the feedback loop) at one stage and decrease by that same amount at another stage and the feedback is not affected.

The scientific description is very clear and there is absolutely no stipulation about the setting of the preamp, channel fader or master fader in the equation:

Quote:
Audio feedback (also known as acoustic feedback, simply as feedback, or the Larsen effect) is a special kind of positive loop gain which occurs when a sound loop exists between an audio input (for example, a microphone or guitar pickup) and an audio output (for example, a power amplified loudspeaker).

Last edited by Samc; 8th April 2018 at 07:16 AM..
Old 8th April 2018
  #138
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mintaka007's Avatar
It sounds like you didn't read my first post, so in relation to gain staging and the gain level vs fader level, here is the pertinent part:

"But there is a 'but'...

The exception is if you have your gain too high on the point of clipping. (If you do this you will almost certainly have your faders set very low to compensate.)

Distortion induced by clipping adds an uncertainty into the feedback equation by changing the balance of frequencies.

The result is not going to be good. In general, distortion adds energy to the higher frequencies. Howlround is always unpleasant but high frequency howlround can be ear splitting.

So set the gain correctly using the normal methods and concentrate on the factors that really can reduce howlround..."

so the gain staging absolutely can effect feedback more than an equal level of fader adjustment, as it adds distortion and added energy at certain frequencies as it approaches clipping. You said earlier that turning down the gain vs pulling down the fader (equal db's) will have the same effect, but you were incorrect in this as if you are not properly gain staged and are near a point of clipping, then you can feedback easier. Therefore, gain staging is important to prevent feedback. This is something taught in nearly every class and textbook on sound reinforcement.
Old 8th April 2018
  #139
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Quote:
Originally Posted by mintaka007 View Post
so the gain staging absolutely can effect feedback more than an equal level of fader adjustment, as it adds distortion and added energy at certain frequencies as it approaches clipping. You said earlier that turning down the gain vs pulling down the fader (equal db's) will have the same effect, but you were incorrect in this as if you are not properly gain staged and are near a point of clipping, then you can feedback easier. Therefore, gain staging is important to prevent feedback. This is something taught in nearly every class and textbook on sound reinforcement.
For clarification I should point out that it goes without saying that I support the application of good gain-staging in audio, but I also know that gain-staging has nothing to do with feedback one way or another.

Can you please link to a paper or article from a reputable source where this is expressly stated, especially a paper or article that explains the science behind this claim. I have never read any such claim from a reputable source and my own experience does not agree with it and I have tested this principle just a couple of days ago.

What about the claim that a cheap preamp/mixer will exacerbate the incidence of feedback...is that your experience and is it also taught in classes and text books on sound reinforcement too?
Old 8th April 2018
  #140
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Wyllys's Avatar
 

Quote:
Originally Posted by mintaka007 View Post
...if you raise the gain by 6 dB, the output from the loudspeakers goes up by 6 dB (assuming no compression). If you then lower the fader by 6 dB, then the output goes down to what it was before.

In fact, however many decibels you change the gain, if you move the fader by an equal number of decibels but opposite in direction, then the output level and loop gain will stay the same.

But there is a 'but'...
One "but" or "gotcha" is that when dealing with faders and pots, in order for these statements regarding consistency of gain staging throughput to be achieved in the real world of mix console controls, LINEARITY of response is required. For those new(er) to the game, fader and knob positioning labels are for mere positional reference and do not necessarily have a 1:1 relationship with the actual signal voltage or units dB.

Quote:
The exception is if you have your gain too high on the point of clipping. (If you do this you will almost certainly have your faders set very low to compensate.)

Distortion induced by clipping adds an uncertainty into the feedback equation...
Simply stated, this condition introduces a non-linearity into the control structure. The physics stay true, but the physical interface/components no longer operate on a level playing field.


Quote:
So set the gain correctly using the normal methods...
Exactly.

Quote:
Originally Posted by mintaka007 View Post
sooooo, what this means is that Samc is correct in that a 6db increase in gain and a 6db decrease in fader movement will net the same spl. Where sam is incorrect is this is only true if you are gain staged correctly. If you are introducing a gain level that is too hot, I.E. hanging out around or above 0 too much, then you can introduce the higher chance of feedback with the spl being the same by lowering the fader.
Sam is not incorrect. You need to understand this in terms of linearity of control, not simply stopping at "too hot". It's not that the stage is "too hot", it's that the component in question is has reached the point of non-linearity due to the set level and literally go "off the charts".

Better preamps will maintain linearity through a greater operational range than those of lesser quality. Terms such as "hot" and "too hot" are street-level labels. You have to understand the underlying phenomenon. Using precise terminology representing actual, measurable quantities when in technical discussion may be compared to proper gain staging when operating audio signal chains.

W

Addendum:

"Non-linear imperfections

The input (yellow) and output (green) of a saturated op amp in an inverting amplifier
Saturation
Output voltage is limited to a minimum and maximum value close to the power supply voltages.[nb 3] The output of older op-amps can reach to within one or two volts of the supply rails. The output of newer so-called "rail to rail" op-amps can reach to within millivolts of the supply rails when providing low output currents.
Slewing
The amplifier's output voltage reaches its maximum rate of change, the slew rate, usually specified in volts per microsecond. When slewing occurs, further increases in the input signal have no effect on the rate of change of the output. Slewing is usually caused by the input stage saturating; the result is a constant current i driving a capacitance C in the amplifier (especially those capacitances used to implement its frequency compensation); the slew rate* is limited by dv/dt = i/C."

Excerpt from: Operational amplifier - Wikipedia

*Slew rate - Wikipedia

Cheaper op-amps saturate sooner...

Last edited by Wyllys; 8th April 2018 at 04:34 PM..
Old 8th April 2018
  #141
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nosebleedaudio's Avatar
 

It IS possible to have clipping and even a latch up issue in a pre amp stage if the gain (Mic Pre) is high and the source hits a peak..
HF distortion goes up more in ANY mic pre at higher gain settings..
I know of SOME high end pres with discrete op amps that had a Latch up problem, Never a good thing...
Old 8th April 2018
  #142
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The salient point in all of this is that the physics of feedback never changes regardless of what happens before...if the sound is broadband or a narrow range of frequencies, distorted or clear is beside the point.

If the conditions are initiated by incompetence or on purpose matters not.
Old 8th April 2018
  #143
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Wyllys's Avatar
 

Quote:
Originally Posted by Samc View Post
The salient point in all of this is that the physics of feedback never changes regardless of what happens before...if the sound is broadband or a narrow range of frequencies, distorted or clear is beside the point.

If the conditions are initiated by incompetence or on purpose matters not.
Ed Zachary!

One common issue in such threads is that we not only have to analyze the case in point but also the statement thereof. Any statements based on subjective personal assessments and charactized metaphorically or in undefined but popular terms (urban myths) only distract from rational discussion.
Old 8th April 2018
  #144
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mintaka007's Avatar
Quote:
Originally Posted by Samc View Post
The science is very clear and does not need translation, none of the text I've ever read on the matter deviates from the fact and nobody has of yet offered a serious argument to support the claims that have been made.

Improper gain-staging and low quality preamps do not 'cause' feedback...

I wish you would make a video showing the relevant measurements.
As I have explained, in very simple terms even, improper gain staging ABSOLUTELY CAN cause feedback. As you approach clipping, distortion and added energy to higher frequencies can cause a higher instance of feedback at a relative volume than if the gain was at a normalized level and the fader turned up to reach the same spl.

Low quality preamps have nothing to do with it--totally agree.

Here is a VERY simple example of why Sam's statement is totally false.

-----Lets say you are doing sound check with the goal of reaching 115db out of the speakers at a given distance. If I improperly gain stage and then turn the gain up to the point of clipping, I will feedback at a lower db, let's say 110, than if I were gain staged properly. If I gain stage correctly, I don't introduce distortion and added high end frequency energy at or near clipping that is not present at a correctly set gain level. This is with ALL other factors that might cause feedback being equal.

So you see, proper gain staging CAN help eliminate feedback. I have explained the physics behind it, and these are well established findings in any sound reinforcement textbook. There is no argument to defend Sam's statement other than he either misspoke or was just plain incorrect.

Sam and Sam's alter ego Wyllys can try to confuse the issue all they want, but the fact of the matter is that this statement by Sam is incorrect.

I have explained why in very simple terms, and if you lack the ability to read or understand this, I can't help you.

One thing I am completely sure about and that is that Sam will never admit he was wrong about something, so my post is for other people who are looking for the correct information. I'm positive there will be a post after this to attempt to still somehow argue the inarguable, so I'll just let whatever post that is sit as I have explained, several times now, how this works.

Gain staging properly is one piece to helping eliminate feedback. Gain staging, mic and speaker/monitor placement(as well as cardioid vs omni, etc), adjusting overall spl level and adjusting eq to minimize a rooms tendency to focus certain frequencies are the biggest things to address to control feedback.
Old 8th April 2018
  #145
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Quote:
Originally Posted by mintaka007 View Post
As I have explained, in very simple terms even, improper gain staging ABSOLUTELY CAN cause feedback. As you approach clipping, distortion and added energy to higher frequencies can cause a higher instance of feedback at a relative volume than if the gain was at a normalized but the all via faded was the same.
You have made a statement, you have not explained it...there is a difference.

Quote:
Low quality preamps have nothing to do with it.
we agree.

Quote:
-----Lets say you are doing sound check with the goal of reaching 115db out of the speakers at a given distance. If I improperly gain stage and then turn the gain up to the point of clipping, I will feedback at a lower db, let's say 110, than if I were gain staged properly. If I gain stage correctly, I don't introduce distortion and added high end.frequency energy at or near clipping that is not present at a correctly set gain level. This is with ALL other factors that might cause feedback being equal.
This is NOT my experience, and I recently tested this, two days ago to be exact.

I have also not found any articles anywhere to support this argument and nobody have as yet posted a link even though you claim that this is in every text book on audio engineering. I dont want a simple statement, I would like a scientific explanation.

Improper gain-staging DOES NOT cause feedback...
Old 8th April 2018
  #146
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Wyllys's Avatar
 

Quote:
Originally Posted by mintaka007 View Post
As I have explained, in very simple terms even, improper gain staging ABSOLUTELY CAN cause feedback. As you approach clipping, distortion and added energy to higher frequencies can cause a higher instance of feedback at a relative volume than if the gain was at a normalized level and the fader turned up to reach the same spl.

Low quality preamps have nothing to do with it--totally agree.

Here is a VERY simple example of why Sam's statement is totally false.

-----Lets say you are doing sound check with the goal of reaching 115db out of the speakers at a given distance. If I improperly gain stage and then turn the gain up to the point of clipping, I will feedback at a lower db, let's say 110, than if I were gain staged properly.
No, this is not true and any further assertions based on this will cannot be valid.

Quote:
... proper gain staging CAN help eliminate feedback. I have explained the physics behind it, and these are well established findings in any sound reinforcement textbook. There is no argument to defend Sam's statement other than he either misspoke or was just plain incorrect.

Sam and Sam's alter ego Wyllys can try to confuse the issue all they want, but the fact of the matter is that this statement by Sam is incorrect.
No, proper gain staging gives a cleaner mix with a minimum of artifacts, but it does not determine or alter the GBF. You have NOT explained the physics...nor the engineering math...involved. Neither have we been given specific references, merely asserting that your assertions are supported by "any sound reinforcement textbook". The Yamaha Sound Reinforcement Handbook (written for Yamaha by Gary Davis and Ralph Jones) is widely accepted as an audio/electronics reference...to the point of being known as "The Bible". I would refer you to pp. 47, 48 and 52 for the answer regarding system GBF. If you're aware of another industry standard text which refutes them, please post it.

The other assertion regarding the purpose of my posts, that I am attempting to "confuse the issue", is a petty personal slur not worthy of inclusion in civilized discussion. I take issue with any and all unsupported statements and assertions you might post, but not you personally.

Quote:
I have explained why in very simple terms...
I think not. The initial premise is flawed and is not supported by any texts I've read. I've included citations in my posts to help in understanding the factors involved in making a cogent assessment of the issue.

The error in such arguments results from an incomplete understanding of how the individual stages function and the effect of operating any stage outside of its design limits as I've tried to explain in bringing up linearity, saturation and the factors involved in establishing ACTUAL level-gain throughput between stages rather than ASSUMED levels.

Simply put, we refer to the issue in terms of GBF (gain before feedback), not GSBF (gains staging before feedback).

Last edited by Wyllys; 8th April 2018 at 09:23 PM..
Old 8th April 2018
  #147
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The Peavey XR8600 has some kind of feedback detection and control in the EQ section. The mixing station pro app for the Behringer XR series has feedback detection. There are other feedback detection and control systems.

I've never understood how these things actually work. Could you please generally explain how these feedback detection systems work?
Old 8th April 2018
  #148
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Wyllys's Avatar
 

Quote:
Originally Posted by 2manyrocks View Post
The Peavey XR8600 has some kind of feedback detection and control in the EQ section. The mixing station pro app for the Behringer XR series has feedback detection. There are other feedback detection and control systems.

I've never understood how these things actually work. Could you please generally explain how these feedback detection systems work?
1. Real-time frequency analysis and

2. Automatic application of notch filters to frequencies exceeding set parameters, usually 1/30 to 1/60 octave filters.

Further features would be adaptive filtering to widen the filters as necessary, fixed/temporary application options and automatic or programable "hold" (duration of application before re-set) and depth of filters.

Understanding Acoustic Feedback & Suppressors
Old 8th April 2018
  #149
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Quote:
Originally Posted by Wyllys View Post
No, proper gain staging gives a cleaner mix with a minimum of artifacts, but it does not determine or alter the GBF. You have NOT explained the physics...nor the engineering math...involved. Neither have we been given specific references, merely asserting that your assertions are supported by "any sound reinforcement textbook". The Yamaha Sound Reinforcement Handbook is widely accepted as an audio/electronics reference...to the point of being known as "The Bible". Can you give chapter and verse from it in support of your claims?
I have been waiting for someone to present documentation that supports this argument from the start to no avail. All I'm reading is that every text book on the subject teaches this and that he's right and we're wrong so I guess we should just throw out decades of experience and accept this.

One thing I've noticed is that everybody who agrees with this claim have given a different argument to support it...no two have agreed on a reason why its so...
Old 8th April 2018
  #150
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Quote:
Originally Posted by Wyllys View Post
The other assertion regarding the purpose of my posts, that I am attempting to "confuse the issue", is a petty personal slur not worthy of inclusion in civilized discussion. I take issue with any and all unsupported statements and assertions you might post, but not you personally.
Did you really expect anything better....
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