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What happens when you push faders past 0db?
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Rjp9
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30th December 2012
Old 30th December 2012
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What happens when you push faders past 0db?

The way I have come to understand simple analog mixers is this: the gain knob controls the (pre)amplification of the weak incoming signal, and the fader merely attenuates the now "resized" incoming voltage. Is this a correct assumption? Can anyone add further nuance?

Also, I've heard that at unity the fader is basically "invisible", acting as an unresisted wire. So what happens when you push a fader past unity level? Are you rerouting that signal back to the preamp for more gain?
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30th December 2012
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Most mixers use the fader in series with a line amp. The line amp commonly has gain of 10 to 20 dB. Your signal goes through the fader and is not re-routed at unity gain. Unity gain on the fader is the point where the fader is attenuating the same amount of gain that the following line amp is adding. Setting the fader above unity gain does not affect the relationship of the fader/amp and is commonly done (that's why the line amp is there....to give you the ability to raise the level of the signal above unity). Of course proper gain staging is critical so you don't drive the signal too hard into the next stage of the electronics.....but that's always the case.
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30th December 2012
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All the gain knobs and faders are attenuators, situated just before fixed gain amplifiers. If the gain knob or fader is fully up there is no attenuation of the signal before it is passed to the fixed gain amplifier.

The 0dB point on the fader is nothing magical, it is just the point where the loss of the variable attenuator (fader) equals the fixed gain of the amplifier stage.

It seems to be a common belief that setting a slider or knob to 0dB results in the least "harm" to the signal. It just isn't so. Your signal must be high enough to have a decent signal to noise ratio, and be low enough that it doesn't clip.

Repeat after me: "All the knobs on the board are attenuators, all the sliders on the board are attenuators." :-)
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30th December 2012
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And as such, faders have nothing to do with gain on your board. That's what the PFL and Trim knob together accomplish.
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30th December 2012
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Quote:
Originally Posted by JC Biffro View Post
It's just one of those 'do not do's' in music.
I knew I was doing something wrong all these years.........now I know what it was!
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30th December 2012
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Quote:
Originally Posted by JC Biffro View Post
To put it bluntly, it sounds like ass.

It's just one of those 'do not do's' in music.
That's the biggest load of bull I've heard this year.

If you don't have adequate S/N, or you distort and clip, then yes, it will sound like ass.

These issues have nothing to do with whether your fader is above or below 0dB.

0dB is a nominal level. Around about where the signal on a channel should be. If you need a bit more X (kick, vocal, whatever) push the fader up. If you need a bit less X, pull the fader down. That's what it is there for.
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30th December 2012
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Quote:
Originally Posted by JC Biffro View Post
Ever thought about lowering everything else, instead of pushing one channel unnecessarily above the threshold?
In a well designed analog mixer it isn't exactly the "threshold of doom".
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30th December 2012
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Quote:
Originally Posted by JC Biffro View Post
Ever thought about lowering everything else, instead of pushing one channel unnecessarily above the threshold?
It ***ISN'T*** a threshold, it is a ***NOMINAL*** level.
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30th December 2012
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If needing to raise one element then surely it would be much easier to just raise that as opposed to lowering everything else? If increasing the volume of one element will 'push one channel unnecessarily above the threshold' then you might not have enough headroom
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31st December 2012
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Great replies everyone! On a quick side note, I wish more posts in this newbie-geared forum were like this--centered on general basic audio discussion rather than the all-too-common "What is the best mic under $100?". Not to say there is anything intrinsically wrong with those kinds of posts (we've all been there); rather, I feel that genuinely productive and enlightening posts get lost sometimes.

So to further the discussion, I will pose another question:

If faders and gain knobs are both attenuators that come before fixed gain amplifiers, then why do we have both? Doesn't it seem redundant to have both? Why don't we just have mixers that only have gain knobs/why don't we just mix with gain knobs instead of faders?

Obviously I know there is a reason that we have both because every conventional mixer has both! I just don't understand why...
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31st December 2012
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The gain knob at the top of a channel is to ensure that the signal level is appropriate for the rest of the electronics in that chain. Set too low and there will be insufficient signal-to-noise. Set to high and the signal will clip and distort.

The fader at the bottom is to set the channel output to asthetically suit the situation.
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31st December 2012
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"...If you need a bit more X (kick, vocal, whatever) push the fader up. If you need a bit less X, pull the fader down..."

Love it. I knew a pilot instructor who used to say, "Push forward on the control to make the houses down there get bigger, and pull back to make them get smaller." Simple can be good.

WW
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1st January 2013
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Quote:
Originally Posted by Bill Way View Post
Love it. I knew a pilot instructor who used to say, "Push forward on the control to make the houses down there get bigger, and pull back to make them get smaller." Simple can be good.
WW
A friend was learning to fly, and was being taught about forced landings at night. The procedure was something like this:

"Glide at stall speed plus 10 knots. At 1000', turn your landing lights on. If things look good, land. If things don't look good, turn your landing lights off..."

:-)
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1st January 2013
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Quote:
Originally Posted by Rjp9 View Post
Obviously I know there is a reason that we have both because every conventional mixer has both! I just don't understand why...
The reason is simple. Once you set the input gain (correctly!) then you can pretty much forget about it - so a simple knob is enough to accomplish that task. But, in the conventional domains where faders are employed, ie. channel faders, busses, and main outs, you need to be able to see at a glance, exactly where those are sitting. It's a kind of visual aid as well as giving you quick access to those functions.

Another thing is that the 100mm fader was invented so that the level of the signal would rise and fall according to how far you either push or pull it up or down.

Another thing is that, with faders, you can grab a whole handful of them at once, for example, you can grab the whole drum set and tweak it up or down at once - try doing that with knobs!
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1st January 2013
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Quote:
Originally Posted by S21 View Post
All the gain knobs and faders are attenuators, situated just before fixed gain amplifiers. If the gain knob or fader is fully up there is no attenuation of the signal before it is passed to the fixed gain amplifier.
I "feel" what you are saying here, but if you don't mind I would like to tweak it slightly. Not all the amplifiers in a console are fixed gain. Look at any mic pre schematic and you will see that the gain knob is actually controlling the "real gain" of the circuit as opposed to simply controlling levels into it. Not all fader buffers are fixed gain either. It really depends on the console designer and how he felt like doing it. You are correct in saying that the goal of fader buffer is to have, say, ten dB of gain at the fader's 0dB point, but I have seen that goal accomplished in many different ways.
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1st January 2013
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Quote:
Originally Posted by JC Biffro View Post
To put it bluntly, it sounds like ass.

It's just one of those 'do not do's' in music.
The Mackie mixer distortion disagrees.
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1st January 2013
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Quote:
Originally Posted by S21 View Post
All the gain knobs and faders are attenuators, situated just before fixed gain amplifiers. If the gain knob or fader is fully up there is no attenuation of the signal before it is passed to the fixed gain amplifier.
Mmmm... I saw a lot of preamp designs where the gain pot actually sits between the opamps input and output as a variable feedback resistor and thus making it a variable gain amplifier. Only the following volume pot then acts as an attenuator. Is this very uncommon for console mic channels?

EDIT: oops, vitalis was faster
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1st January 2013
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Quote:
Originally Posted by chk23 View Post
Mmmm... I saw a lot of preamp designs where the gain pot actually sits between the opamps input and output as a variable feedback resistor and thus making it a variable gain amplifier. Only the following volume pot then acts as an attenuator. Is this very uncommon for console mic channels?
Some consoles actually are designed that way. The mic gain is switchable in fairly large steps, just to get you in the ballpark, and then there will be a "fine tuning" knob to set the gain exactly. Neve pre's are like that, as well as some other "old school" boards. It's not done so much in today's consoles simply because of the cost. A good quality switchable attenuator can run you up to 200 bucks or so. Like yourself, I have also seen this setup in standalone pre's with +/- ten dB or so extra gain. In that situation a manufacturer can afford to do it because it adds to the pre's flexability as well as to it's mystique.
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1st January 2013
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Quote:
Originally Posted by JC Biffro View Post
To put it bluntly, it sounds like ass.

It's just one of those 'do not do's' in music.
Not really. The reason for the extra 10dB gain in the fader circuit is to use it if you need it. The console designer has no idea what signals you are putting into the console, so it could be that by the time you get to the channel fader, for example, maybe you've got too much or too little signal level. Maybe you just got distracted, or maybe you got rushed and didn't have time to set things up correctly. So what are you going to do then? You're up against the wall with musicians who are costing you a million bucks an hour. You can't simply stop the take and say; "can you give me more level?" No, you grab that fader and push it up! You know, the last thing you need is the guitar player saying; "well why is my guitar so low in the mix?" Are you going to say; "well, I didn't want to push the fader over 0dB". Good luck trying to explain that to the poor guy!
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1st January 2013
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Quote:
Originally Posted by Vitalis View Post
I "feel" what you are saying here, but if you don't mind I would like to tweak it slightly. Not all the amplifiers in a console are fixed gain. Look at any mic pre schematic and you will see that the gain knob is actually controlling the "real gain" of the circuit as opposed to simply controlling levels into it. Not all fader buffers are fixed gain either. It really depends on the console designer and how he felt like doing it. You are correct in saying that the goal of fader buffer is to have, say, ten dB of gain at the fader's 0dB point, but I have seen that goal accomplished in many different ways.
Yes, I was glossing over things a bit, eh? Real variable gain amplifiers do exist, but are rare compared to their fixed gain cousins. Opamps with attenuated feedback are fixed gain devices in my book, but I agree your perspective on the problem is also valid.

The real point I was trying to get across was that there isn't a magical 0dB point where these circuits are delivering unimpaired "wire-like" connectivity.
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1st January 2013
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Quote:
Originally Posted by S21 View Post
The real point I was trying to get across was that there isn't a magical 0dB point where these circuits are delivering unimpaired "wire-like" connectivity.
Yes, absolutely, because no matter how that circuit is designed you still have to go through it with your audio. You certainly can't bypass it. If the fader is before that +10dB amp, well all you are doing is controlling the level into that amp, and if the fader is more used to controll the actual gain of the amp you still have to go through the whole amp anyway, so you are correct in saying there is no magic 0dB point.

It's amazing how many old wives tales are going on out there, you know, some guy said this and someone heard that. I guess you could spend a lifetime just fighting against stuff like that.
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2nd January 2013
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Quote:
Originally Posted by S21 View Post
Real variable gain amplifiers do exist, but are rare compared to their fixed gain cousins.
Could you expand on the differences between the two? Why are there different circuit designs?

Quote:
Originally Posted by S21
The real point I was trying to get across was that there isn't a magical 0dB point where these circuits are delivering unimpaired "wire-like" connectivity.
Thank you for clearing that up!

Quote:
Originally Posted by Vitalis
It's amazing how many old wives tales are going on out there, you know, some guy said this and someone heard that.
Kind of why I wanted to start this thread! Wanted to clear some stuff up.
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2nd January 2013
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Quote:
Originally Posted by Rjp9 View Post
Could you expand on the differences between the two? Why are there different circuit designs?
There are many reasons for different designs: Cost/parts availabilities, different applications, different engineering philosophies...

An opamp with variable gain comes in handy, for example, with automated faders were you want to control the gain by a voltage level instead of changing the resistance within the audio path/feedback loop directly by a potentiometer.
You can find out more on wikipedia about variable gain amplifiers and the applications they're used for.
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4th January 2013
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Hi
Rick Sutton and S21 answers are accurate (although would probably take half a paragraph to fully explain what they are saying). Some of the other answers are specious to say the least.
The object of the 'gain' control is to get a signal that can vary from about -80dBu to +25dBu to a suitable 'standard' or 'nominal' level which has sufficient voltage headroom available to avoid accidental clipping, but not so low that it is noise ridden.
This can be achieved by amplifier stages with variable gain (usually best to get lowest noise figures) or with one or more fixed gain amplifiers with combinations of attenuators around them. Cost of pots and switches involved have significant bearing on this process.
This 'nominal' level is then typically taken (possibly through an EQ section) to a 'fader' which is essentially an attenuator which as mentioned previously has attributes of high physical visibility, ability to control several at once easily, and sufficiently large physical scale so that fine adjustments can be made. These usually 'hold' about 10dB 'in hand' from their 'nominal' position such that an initial setup has all faders at around 'nominal' and adjustments can be made from that position.
There is a lot of 'tradition' involved but the nominal position can actually be anywhere you like with either no 'extra' available, or having 20dB or more available. Obviously with no extra, if you want a couple more dB on a channel you have to start adjusting the gain control (which may be a switch so would 'jump') or with more than 20dB available there is some risk of compromising noise performance.
There are many different circuit designs available in a 'quest' to find 'the best performance' although it would be fair to say that for any given design the optimal gain range is in the order of 30 - 40dB otherwise distortion or noise can become intrusive.
There are other particular problems with designs using 'pots' for gain changing in that the 'resolution' near maximum gain can be pretty wild due to the necessity of providing very small resistance changes over a small physical 'arc'.
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5th January 2013
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Quote:
Originally Posted by Matt Syson View Post
Hi Rick Sutton and S21 answers are accurate (although would probably take half a paragraph to fully explain what they are saying). Some of the other answers are specious to say the least.
I believe that the best and most accurate answer is one which takes into account the understanding and education level of the one who originally posted the question. It doesn't help that person at all to give a reply which is over his / her head. If the OP could understand what you said in your post then he wouldn't have needed to ask the question that he did.

Also, if you disagree openly with another technician, then you should do it in humbleness and respect.
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5th January 2013
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You need to tell some white lies (and lies by omission) to explain anything simply.

When I studied chemistry each year they would tell us "last year we lied to you about how things work, but this year you will learn the truth." Year after year after year.

The first set of lies worked in 95% of circumstances.
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5th January 2013
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Hi Vitalis
Sorry I should have included you among the couple who's answers are most 'accurate'.
It was not a 'personal snub' but you had not said as much about the subject as the others up to that point.
You should not necessarily 'pre judge' the intelligence level of any respondent and a little 'stretching' of anyone's boundaries is always good as long as it is taken incrementally.
The OP could read what is written but happily 'step off' at any point where they feel it is too intense or they get 'bored'.
Anyone who disagrees with anything I have written is of course free to disagree although it would be good manners for them to explain exactly WHY with examples, as on many subjects I do actually go and MEASURE various phenomenen to verify the claim.
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5th January 2013
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Quote:
Originally Posted by Matt Syson View Post
You should not necessarily 'pre judge' the intelligence level of any respondent and a little 'stretching' of anyone's boundaries is always good as long as it is taken incrementally.
It wasn't an issue of me feeling snubbed by you. I am secure in what I know and in what I don't know - so I don't really need anybody else's approval. It was an issue of you claiming that others were wrong and then proceeding to add nothing to what had already been said.

It's also not an issue of "prejudgment". This part of the GS forum is clearly geared towards "Newbies", so they have prejudged themselves by posting here - and I think that that's fine. The reason they post here is because they want to go away having understood something, as opposed to being looked down on because they don't know something.
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6th January 2013
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Hey guys, OP here. The way I see it, the purpose of this specific "newbie" forum is to generate useful discourse to help amateur and home recording engineers such as myself. Any information (that is truthful) is helpful, whether it is over my head or not. Of course it does help if someone breaks down concepts (I prefer this to the term "lying" haha) to make things easier to understand--even in real life they are more complex. However, just having a response typed by a fellow human interested in audio recording is always cool. I may not understand everything said on this thread, but at least I know different gain designs exist!! Better to have a cloudy picture than none at all.
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