gain vs. volume fader

[joelbah]

Sorry, this might be a noob question...I don't run sound, I play guitar, but I have been forced to run sound on many occasions, and I think I have a pretty good ear, but I rarely know how to make things sound like I want them to...anyway, I am pretty sure the guy who runs the board for my band doesn't really know all that much either.

 

Here's my problem. I think our sound guy just sets the gain at a pretty low level to make sure that the signal doesn't peak and then he boosts the slider to the appropriate volume level. But I have worked with other more experienced audio engineers that always ask me to play as loud as I am ever going to play while they are checking my guitar signal. I think this is because they are turning up the gain as high as possible without having the signal peak. From my experience it seems that if you really try to push the gain level, the signal is more pronounced, clear, and just has higher overall quality. Is this true or am I just hearing things? Should you always try to turn up the gain up until the signal is about to peak?

 

Two more quick questions...some boards have a trim knob and some have a gain knob. These are the same thing right?

 

also, I have heard that if you are having feedback problems, one solution can be to turn down the gain a bit and boost the slider...why does that work? does turning up the gain sort of compress the signal?

 

Basically if someone could explain all the differences between the gain control and the volume slider and also how to use them both effectively, it would probably answer all my questions. Thanks...I have a show tonight so prompt answers will be appreciated.

[the stranger]

Trim and gain are usually the same thing...

 

The trick is to get everything set at unity gain. You do need to have a player play his loudest passage. When he is doing that, I will have the fader at unity and bring up the trim/gain until I get an acceptable signal level. After that, it's up to the engineer to ride the levels appropriately and/or use compression/limiting to control the signal peaks.

 

Regardless, set the fader at unity and adjust the rest to reach good signal level. Compromise any rules if something sounds better!

 

Cheers!

[blue2blue]

I'm pretty sure stranger doesn't mean to leave the faders at unity.

 

But when you have a board that doesn't have a full metering bridge for inputs (as with many small home recroding and PA boards), you end up having to use the bus meters when you're setting the channel trim pots.

 

That's why you set the channel fader (and the bus fader if the meter you're using is post fader) to unity -- because you want the meter to accurately reflect the level coming off the gain trim pot.

 

And, yes, you basically want to set the trim to an optimal level for the loudest sound the source is going to make.

 

That will give you an optimal signal going through the mixer channel.

 

Of course, from there, you go ahead and use your channel faders to set your mix.

[joelbah]

 

And, yes, you basically want to set the trim to an optimal level for the loudest sound the source is going to make. That will give you an optimal signal going through the mixer channel.

 

 

When you say optimal signal, do you mean it will actually sound better? or are you just saying it gives you the most power incase you really need to boost the slider?

[blue2blue]

 

When you say optimal signal, do you mean it will actually sound better? or are you just saying it gives you the most power incase you really need to boost the slider?

 

Well, my comments assumed it was an analog mixer, for one thing. I realized after I wrote that that I should have pointed it out. (Proper gain optimization is important in either but the tradeoffs tend to be a little different.)

 

With an analog board, your main enemy is self-noise of preamps and gain makeup stages at one extreme and overload distortion at the other.

 

If you set your gain levels inappropriately, you can end up with both: for instance, let's say you open up your trim pot too high and then, to compensate for that, you lower the channel fader. You end up with increased preamp self-noise and a signal that's potentially too hot for the channel circuitry, causing overload distortion.

 

You might even compound the error by turning the channel fader down too far and then having to boost the master fader -- resulting in more self noise assuming the mix bus is active [has gain compensation amplification].

 

 

If you're using a digital board, self-noise from analog preamps is still a consideration but you also potentially might have to worry about digital resolution issues if you gain stage poorly.

[MikeRivers]

 

I think our sound guy just sets the gain at a pretty low level to make sure that the signal doesn't peak and then he boosts the slider to the appropriate volume level.

That's a safe way to do it, particularly if you have to leave the console and go off to play your guitar. Ideally, you should get all the gain you need in the first stage (the TRIM or GAIN pot, if any) and then amplify that as needed to get the mix balanced and the volume high enough.

I have worked with other more experienced audio engineers that always ask me to play as loud as I am ever going to play while they are checking my guitar signal. I think this is because they are turning up the gain as high as possible without having the signal peak.

That's correct, and that's a good way to do it too. An experienced engineer will know that you will always play louder on stage and compensate for it with a conservative setting.

From my experience it seems that if you really try to push the gain level, the signal is more pronounced, clear, and just has higher overall quality. Is this true or am I just hearing things?

You're probably just hearing things - possibly you're just hearing it louder, which makes everything sound better. But there are exceptions, and there's exceptionally bad gear, so from here, I can't tell what you're hearing.

Should you always try to turn up the gain up until the signal is about to peak?

Only if you can be there to make sure that it never clips. A technique that works pretty well for me is to start with the faders all at their design center (sometimes called "unity gain") position, get the band playing, and use the Gain pots to do a rough mix, juggling the master fader along with the trims to avoid clipping or too far below clipping. There's no best method for doing this. It's whatever works considering everything that's going on with a live show.

..some boards have a trim knob and some have a gain knob. These are the same thing right?

Usually. But some have only one knob, and it's often marked GAIN.

also, I have heard that if you are having feedback problems, one solution can be to turn down the gain a bit and boost the slider...why does that work?

It doesn't work.

does turning up the gain sort of compress the signal?

Yes, but it distorts badly in the process. The way to fix feedback is to reduce the gain between the microphone and the speaker and there are no knobs on the console for that. You can reduce the console gain at the feedback frequency but you have to be careful about that. If you don't have a narrow band filter and set it accurately, you can take away clarity. And there's usually several feedback frequencies, not just one. And they change with temperature and distance.

Basically if someone could explain all the differences between the gain control and the volume slider and also how to use them both effectively, it would probably answer all my questions.

 

Read the Mackie Compact Mixer Reference Guide

[joelbah]

it seems like there is about the same number of people saying opposite things. one side says that the more gain the better it will sound and the other saying it shouldn't matter, volume from the slider or volume from the gain knob.

 

I don't know who to believe.

 

I would just test it on the system tonight but I probably won't have enough time to do that.

[blue2blue]

I don't think people are really saying too much different here. (I do have some qualms about how Mike described what he was doing with the faders at unity gain, as you may infer from my summary below.)

 

One quick note: in essence, unity gain means a 1:1 amplitude ratio, the amplitude in that position is neither increased nor diminished.

 

Here are the places where you control level in a typical mixing board:

 

The trim pot -- this essentially controls the gain of the preamp stage. You want this high enough to get above the preamp's noise floor and low enough so that you don't overload it or the next stage. (A mic pre might have multiple points of gain control but most mixers simply have one.) So you will always shoot for a "just-right" level, here. (An important note: some boards have a trim control that only works on the mic input, passing the line input through at unity. Other boards have a trim that works on both the mic and line ins.)

 

The channel fader -- as I noted, when setting channel levels with the trim using the bus meter, you'll keep the channel fader for the channel your working with at unity gain while you adjust the input trim. But when you're done setting the trim, this is where you will do your mixing of relative levels from one channel to the next (after all channels' trims have been optimized).

 

Finally, your master fader. If you have a separate power amp that has an input volume, you'll likely want to set that so that having your mixer's output fader at its own unity gain setting gives you just the right level in the room. (Of course, most sound checks are done in an empty house, so experience will dictate a conservative position, there, as a bunch of warm bodies will soak up a lot of level.) But you can use this to make small adjustments to overall level as needed.

 

Hope that helps.

[BlueStrat]

Trim and gain are usually the same thing... The trick is to get everything set at unity gain. You do need to have a player play his loudest passage. When he is doing that, I will have the fader at unity and bring up the trim/gain until I get an acceptable signal level. After that, it's up to the engineer to ride the levels appropriately and/or use compression/limiting to control the signal peaks. Regardless, set the fader at unity and adjust the rest to reach good signal level. Compromise any rules if something sounds better! Cheers!

 

 

Yep.

[blue2blue]

I'm afraid that some people are going to read that and think that they're supposed to leave the channel faders at unity gain once the trim levels are set.

 

In general, the main time you're going to specifically set a channel fader at unity gain is when you're setting the trim level for that channel and you're using a bus meter to set the level. (As on a board that doesn't have channel metering. If the meter you're using is post bus-fader, you'll also want the bus fader at unity gain.)

 

After that -- when mixing -- you set the level needed for that channel in the mix with the channel fader... maybe that's -12 dB, maybe it's -20, or maybe it is 0 dB.

 

If the source material changes level significantly -- then it may be appropriate to readjust the trim in order to reoptimize the gain structure for that channel.

 

It probably makes me sound compulsive to go on -- but I've found over the years a lot of confusion. I actually won a bet when I was in recording school about this precise question. (The guy welched but that's another story. He was humiliated -- and that's what's important. )

[the stranger]

I was assuming he was looking for a quick and dirty answer. I edited out a longer description that went on about all these other variables, but he just needs to get things in the ballpark. And I do think on a per channel basis, the method I described is the best bet. I assumed even a novice would understand that leaving the faders and gain the same the whole time wouldn't be mixing.

 

In general, the main time you're going to specifically set a channel fader at unity gain is when you're setting the trim level for that channel and you're using a bus meter to set the level. (As on a board that doesn't have channel metering. If the meter you're using is post bus-fader, you'll also want the bus fader at unity gain.)

 

Yes. He says it better than I do.

 

After that -- when mixing -- you set the level needed for that channel in the mix with the channel fader... maybe that's -12 dB, maybe it's -20, or maybe it is 0 dB. If the source material changes level significantly -- then it may be appropriate to readjust the trim in order to reoptimize the gain structure for that channel.

[the stranger]

Just as an example, I could see a situation where driving the preamp on a channel and using a lower fader level may result in a better sonic result. Generally, most mixers (the mic preamps, channel electronics) are engineered to operate best when in a given range. Which is the reason for the original suggestion...but anything goes. What sounds better?

 

Maybe this would be better:

 

1. Set master fader at unity gain.

 

2. Set channel fader at unity and adjust trim/gain to achieve optimal signal level. Repeat for all channels. This should have your mic preamps in the ball park.

 

3. Drop all the faders. Start mixing. Because what is going to happen is when all these signals come together in the master bus may require adjustment all throughout the signal chain.

 

If you set everything at unity and leave it that way, I'm sure you would end up with a distorted mess.

[Rudolf von Hagenwil]

But unity gain is defined as when input and output are at the same voltage level and impedance, right?

 

In other words, when all gain knobs and fader are at 0 dB (no gain change) that would be one case of unity gain, but when you raise the input trim by 3dB, you also have to raise the fader and the master fader to by 3dB to still be in unity gain, right?

 

If so, to keep all in unity gain is practically impossible, right?

[the stranger]

Probably. http://www.google.com/search?sitesearch=en.wikipedia.org&q=unity+gain&fulltext=Search

 

But, for lack of a better term and all...I think some mixer manufacturer is to blame for my misappropriation of terminology. "Optimal gain"?

[the stranger]

 

But unity gain is defined as when input and output are at the same voltage level and impedance, right? In other words, when all gain knobs and fader are at 0 dB (no gain change) that would be one case of unity gain, but when you raise the input trim by 3dB, you also have to raise the fader and the master fader to by 3dB to still be in unity gain, right? If so, to keep all in unity gain is practically impossible, right?

 

 

But...at what range is the preamp operating at unity or optimal operating range?

 

I still think the original question was primarily directed at the issue of channel fader and gain/trim knob. I think the most important first step is to establish a good level hitting the fader. If you set the fader at unity, this allows you to set the preamp (gain/trim) level at a point that won't clip (or be too low) when you bring up that fader in the mix.

[Rudolf von Hagenwil]

"Optimal gain" sounds good but requires that the mixer knows in what range his material sounds best and where the limits are where after it starts to sound bad. When the microphoes are plugged directly into the mixer, the input trim is reserved for adjusting the microphone level. I'm no live engineer, but the basics must be the same as in the studio. I would guess first class live engineering applies a flexible calibration with enough power reserve at the amps to maintain highest quality sound and the ability to adjust to the required loudness for any room size.

 

At live events I believe to observe that the power amps are fix at full volume, sometimes have no volume knobs to amplify the optimal sound from the mixer to the required loudness in the hall. In other words, the power amps are constantly at maximum output and when that maximum is not enough energy to get the required loudness, the mixer pushes fader gain stages to above of what sounds good, or maybe the power amps at full volume do not match the speaker cabinets. Simply said, use the mixer only to mix and the power amps to make the loudness for the hall.

 

For my live sound expectation a similar calibration and loudness standard as in the THX/Dolby mix stage would be adequate. The sound at the The Greek Theatre and in the Hollywood Bowl was always first class, almost studio quality, but I guess they have a first class acoustic irradiation philosophy there. I am not sure if it is possible to maintain highest quality sound with the loudness some rock bands require.

 

It would be interesting to know how live engineer make a high fidelity concert sound. The Barbra S. concert in Z

[the stranger]

I ran live sound once for a benefit gig. Long story short: Live sound is far more intensive than any studio recording. But, I followed the same principles I use in the studio and managed to get what I felt was acceptable results with what I had to work with. And it wasn't much. One of the guys was concerned I wasn't going to be sending him a monitor feed. Problem was, I was mixing using a 12 channel powered board, and a head type PA in parallel just to get enough volume. Couldn't spare the juice, I told him. It wasn't like I was feeding his custom in-ear system. Aside from him, I got some glowing comments and was pleased to have contributed to a worthy cause. The benefit was for a guy that was cool, but chose to succumb to the evils of heroin addiction.

 

Gig was outdoors...for the first set-up/tear down/set-up cycle

due to rain and The Police. Not the band, the authorities. Actually, the cops shut the bar down at like 10:30. Earlier they just made us move inside (lack of a permit). Then we tried to set-up inside a room the size of one car garage that was filled with people. Sardines. I would guess three times the legal limit of people in this establishment. I was getting a bit agitated at people's obvious obliviousness to the fact that they were in the way! Impatient from the lack of sound, yet not willing to assist the cause. Hosers! We did manage to get set-up and I did the best I could dealing with the vocalist that wasn't loud enough.

 

He was doing that whole "giving me the look" thing. I told him I had it pegged and that the drums combined with a bass amp and two guitar amps in this one car garage [the bar] was hard to overcome with this loaner we got for the gig.

 

As soon as the first thrashing band hit, mayhem and exponential violence ensued. Man wants chaos. The bar cleared out for some redneck brawl from hell. These people were drunk when I got there at 2:30. They were wasted by 6:00. And right after the brawl went outside later that evening, law enforcement from three countries stormed the bar and surrounding neighborhoods.

 

They declared martial law and closed the bar. The seediest bar in town. Can you spare a cigarette?

[blue2blue]

 

Just as an example, I could see a situation where driving the preamp on a channel and using a lower fader level may result in a better sonic result. Generally, most mixers (the mic preamps, channel electronics) are engineered to operate best when in a given range. Which is the reason for the original suggestion...but anything goes. What sounds better? Maybe this would be better: 1. Set master fader at unity gain. 2. Set channel fader at unity and adjust trim/gain to achieve optimal signal level. Repeat for all channels. This should have your mic preamps in the ball park. 3. Drop all the faders. Start mixing. Because what is going to happen is when all these signals come together in the master bus may require adjustment all throughout the signal chain. If you set everything at unity and leave it that way, I'm sure you would end up with a distorted mess.

 

 

I know that probably seems overly explicit to most of us -- but if you'd read all the confused newbie posts I have, you'd have a deep appreciation for how much knowledge most of us who've been doing it a while take for granted.

 

I read posts by people who have 10's of thousands of dollars worth of equipment and can't get the simple stuff straight in their heads.

[blue2blue]

 

But...at what range is the preamp operating at unity or optimal operating range? I still think the original question was primarily directed at the issue of channel fader and gain/trim knob. I think the most important first step is to establish a good level hitting the fader. If you set the fader at unity, this allows you to set the preamp (gain/trim) level at a point that won't clip (or be too low) when you bring up that fader in the mix.

 

 

Right... you want unity gain in between the trim pot you're currently setting and the point where it's being metered.

 

In Angelo's world, most of the boards probably have big, gleaming meter bridges -- one for each channel -- and setting the trim is a pretty direct process. Set the fader at unity (assuming the channel meter is post-fader) and set the trim to level optimized for maximun gain without distortion, using the meter as a guide.

 

In the world I now inhabit, individual channel metering is rare so us cheapskate, shoestring guys use the bus metering to set our levels (typically requiring both the channel and bus faders to be at unity so that the meter is reflecting the 'full' level of the signal coming from the trim without any extra amplification). Obviously, we have to make sure we're only metering the channel in question, so we typically solo it. (Again, we're assuming the bus metering is post-fader.) And then, of course, once we've optimized the input gain, we go ahead and mix, setting channel faders as needed.

 

Anyhow... I'm sorry to go on with such compulsively rabbinical attention to detail and stickling here but, dang, you should see some of the stuff I read on GS and elsewhere.

 

Many of us took years learning how to do analog audio basics -- and that was when things were relatively simple. But now many of us have also loaded all this digital theory and practice into our heads, too, and we tend to think of analog basics as elementary. And while they may be elemental -- it's still no easier for today's newbies to grasp than when we were young.

 

Unfortunately, the notion that it takes years to properly learn recording is completely up in smoke with a lot of folks coming up. They often seem to think they're smarter than the old guys and that the old rules don't apply to them. Of course, a lot of them don't understand the most elementary things about digital audio, either, but that's for some other thread...

[blue2blue]

was hard to overcome with this loaner we got for the gig. As soon as the first thrashing band hit, mayhem and exponential violence ensued. Man wants chaos. The bar cleared out for some redneck brawl from hell. These people were drunk when I got there at 2:30. They were wasted by 6:00. And right after the brawl went outside later that evening, law enforcement from three countries stormed the bar and surrounding neighborhoods. They declared martial law and closed the bar. The seediest bar in town. Can you spare a cigarette?

 

There was a time when I thought I was better than the live sound guys... and when I'd done live sound gigs, I'd mostly worked on tinky club PAs and things were pretty minimal.

 

But somehow me and one of my engineering buddies got roped into doing sound in a 1500 seat venue for this rockabilly show headlined by a band whose young manager clearly thought they were going to be the next big thing.

 

The PA we had to use was quite underpowered for the venue (thanks to the promoters who handled all that -- mistake one) and hinky, to boot, with some funky channels -- which we needed to use...

 

Sound check was hell. The performance was a nightmare. We got through it but I absolutely swore off live sound then and there. Leave it to the experts... and let me push my little faders in the relative sanity of a properly lit control room.

[mobobog]

Is there any situation when you had to have the channel fader ABOVE unity gain? (after setting the gain level right of course)

[blue2blue]

Yes... but it's all too easy to get into fader creep... you push up the drums and then the bass needs to come up and before you know it the gjuitars have to come up and then the vocalist comes in an says, hey, the vocals are buried... and before you know it, you're overloading the buss and getting distortion. (And, depending on your levels, even a single channel could drive the buss into distortion.)

 

 

It's a little like running a complex irrigation network...

[philbo]

There was a time when I thought I was better than the live sound guys... and when I'd done live sound gigs, I'd mostly worked on tinky club PAs and things were pretty minimal. But somehow me and one of my engineering buddies got roped into doing sound in a 1500 seat venue for this rockabilly show headlined by a band whose young manager clearly thought they were going to be the next big thing. The PA we had to use was quite underpowered for the venue (thanks to the promoters who handled all that -- mistake one) and hinky, to boot, with some funky channels -- which we needed to use... Sound check was hell. The performance was a nightmare. We got through it but I absolutely swore off live sound then and there. Leave it to the experts ... and let me push my little faders in the relative sanity of a properly lit control room.

 

Yeah, mixing live sound is so exciting!! Because each and every time has the potential to become anything between a total nightmare and a very satisfying and fun time.... Never a dull moment.

[lsits]

Pardon my ignorance, but I thought that you should set the input gains by using the PFL button on each channel to get the hottest signal before distorting, then using the faders to set the levels.

[blue2blue]

If you've got a PFL (pre-fader-listen [it's kind of like a pre-fader solo]) then, yeah, that's the most direct way.

 

Many affordable, small format or just plain older mixing boards don't have PFL.

 

It's a good feature to have, for sure!