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  #1  
Old 10-16-2018, 11:31 PM
Roivas Roivas is offline
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Default Mbox3 Pro: +4 Line Input Unity Gain

I don't own one, but use them frequently at a regular freelance gig.

When using this interface in combination with an external preamp sending out +4 line level via 1/4" TRS, what is unity gain on the knob in the front of the MBox3? I'm assuming it's all the way down (counter clockwise).

A couple of times, I've gone to this studio to find the knob at 12 o'clock from a previous session. Before I mention this and look like an idiot, can someone from Avid confirm that the channel's gain knob should be all the way down when it's receiving a normal, +4 line level signal from an external preamp?

The manual seems rather quiet on this matter.

Thanks...
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  #2  
Old 10-16-2018, 11:48 PM
Darryl Ramm Darryl Ramm is offline
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Default Re: Mbox3 Pro: +4 Line Input Unity Gain

You really should be gain staging this with your ears.

But to understand stuff... you have everything you need to answer all these questions in front of you.

Signal Gen in Pro Tools. Sine wave output. Confirm the analog level output with an multimeter. Then probe the line (and outboard mic) inputs with that signal. You can mark gain marks on the knob if you want to.

(and are other folks engaging the -10dB pad? And why?)
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  #3  
Old 10-18-2018, 12:07 PM
Roivas Roivas is offline
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Default Re: Mbox3 Pro: +4 Line Input Unity Gain

Quote:
Originally Posted by Darryl Ramm View Post
You really should be gain staging this with your ears.

But to understand stuff... you have everything you need to answer all these questions in front of you.

Signal Gen in Pro Tools. Sine wave output. Confirm the analog level output with an multimeter. Then probe the line (and outboard mic) inputs with that signal. You can mark gain marks on the knob if you want to.

(and are other folks engaging the -10dB pad? And why?)

Hello. Thanks for responding, although I can do without the "mansplaining".

There's a -20 pad that can be engaged by pulling the gain knob out. I've never seen this messed with, but the line input switch in the back of the unit is sometimes set to -10 unbalanced line level. Why is this being done? I have no idea. I just make sure I'm at +4 before I get signal going.

This isn't the kind of gig where I have time to calibrate everything before a session with a voltmeter. I just need to know what unity gain is as far as setting the knob in front.

I assume that if it's all the way down counter-clockwise, no gain is being added and this is pretty much unity gain (as close to bypassed as you can get). I've used the outboard preamp they have there hundreds of times so the MBox is the only thing I'm not used to. As far as what I see in Pro Tools the levels look "normal" when the knob is set this way. Also I'm having no issues with noise or headroom.

If you read into this a little more, it's might be fairly obvious that I would prefer the information come from Avid than from me as far as my employer goes. Make sense?

Last edited by Roivas; 10-18-2018 at 12:25 PM.
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  #4  
Old 10-18-2018, 12:33 PM
Darryl Ramm Darryl Ramm is offline
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Default Re: Mbox3 Pro: +4 Line Input Unity Gain

Unlikely anybody from Avid is going to read this or reply. This is a user forum.

Unlikely most active users here have an Mbox. And unlikely other users here know the exact answer or care to make the measurements you can make in several minutes yourself.

I could be but I would not assume any gain knob on any device is OdB at any extreme. If it is important measure it.
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  #5  
Old 10-18-2018, 12:54 PM
Roivas Roivas is offline
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Default Re: Mbox3 Pro: +4 Line Input Unity Gain

Quote:
Originally Posted by Darryl Ramm View Post
Unlikely anybody from Avid is going to read this or reply. This is a user forum.

Unlikely most active users here have an Mbox. And unlikely other users here know the exact answer or care to make the measurements you can make in several minutes yourself.

I could be but I would not assume any gain knob on any device is OdB at any extreme. If it is important measure it.
If it were my personal interface, I would take the time to do this. As a freelance recordist at this particular gig, I have to jump in and GO GO GO. Not ideal, but it is what it is. Just wanted a simple answer so I can send out an email to the staff engineers.

I once had the "chief engineer" (whatever that means) at some dump in DTLA argue with me about how the BAE 1073 output trim knob should always be at 12 o'clock (unity gain, right? LOL). I always set it fully clockwise (as your supposed to...it's a trim knob). In this case I could point him to the manual which stated: "OUTPUT KNOB
The output knob (grey) should be fully clockwise to achieve the highest headroom am [sic] cleanest signal path."

If it were the 500 series Neve 1073LB, the output knob can add a little gain, so he would be more correct in that case.

Thanks again, but unfortunately the issue is more politics than me just being curious about the mysteries of gain staging and all that.
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  #6  
Old 10-18-2018, 12:46 PM
BScout BScout is offline
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Default Re: Mbox3 Pro: +4 Line Input Unity Gain

Quote:
Originally Posted by Roivas View Post
Hello. Thanks for responding, although I can do without the "mansplaining".
It's just explaining when no one knows what your gender is. He's explaining a simple loop back to see if there is gain. The multimeter isn't even necessary. You only need to do it once on one Mbox3 Pro.
Quote:
Originally Posted by Roivas View Post
If you read into this a little more, it's might be fairly obvious that I would prefer the information come from Avid than from me as far as my employer goes. Make sense?
Nicely passive aggressive. This is a community forum. If you want direct help from Avid and only Avid, they have the Avid Support Center paid-for support. You can buy a code and get help only from Avid.
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  #7  
Old 10-18-2018, 01:26 PM
Roivas Roivas is offline
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Default Re: Mbox3 Pro: +4 Line Input Unity Gain

Quote:
Originally Posted by BScout View Post
It's just explaining when no one knows what your gender is. He's explaining a simple loop back to see if there is gain. The multimeter isn't even necessary. You only need to do it once on one Mbox3 Pro.
I'm a dude, relax. I would've preferred a simple answer to the question. No lectures about gain staging were needed.

I can't be hanging out after my sessions there to run tests on their interfaces. It's not that kind of situation. I have no problem RTFM, but it's not helpful.

Last edited by Roivas; 10-18-2018 at 01:44 PM.
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  #8  
Old 10-18-2018, 02:04 PM
Darryl Ramm Darryl Ramm is offline
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Default Re: Mbox3 Pro: +4 Line Input Unity Gain

Quote:
Originally Posted by Roivas View Post
I'm a dude, relax. I would've preferred a simple answer to the question. No lectures about gain staging were needed.

I can't be hanging out after my sessions there to run tests on their interfaces. It's not that kind of situation. I have no problem RTFM, but it's not helpful.
Well besides the RTFM part which would have explained you are using the wrong input for line level.
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  #9  
Old 10-18-2018, 01:00 PM
Darryl Ramm Darryl Ramm is offline
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Default Re: Mbox3 Pro: +4 Line Input Unity Gain

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Originally Posted by Roivas View Post
...but the line input switch in the back of the unit is sometimes set to -10 unbalanced line level. Why is this being done? I have no idea
I misread this thread in the first go as an Mbox 3 not an Mbox 3 Pro... I mean why would somebody be asking this question with a Pro? So let me point out its all a complete waste of time. The Mbox 3 *Pro* became clear to me on mention of +4/-10 line input switches.... they are there in the Pro because the line input bypasses the mic preamp in that model. So gain settings make no effect assuming you are using the correct frigging line input... so why are you using the wrong physical input to start with?

If you would prefer an Avid employee to ask you that question you can purchase a support ticket and contact Avid support.
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  #10  
Old 10-18-2018, 01:04 PM
Roivas Roivas is offline
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Default Re: Mbox3 Pro: +4 Line Input Unity Gain

Quote:
Originally Posted by Darryl Ramm View Post
I misread this thread in the first go as an Mbox 3 not an Mbox 3 Pro... I mean why would somebody be asking this question with a Pro? So let me point out its all a complete waste of time. The Mbox 3 *Pro* became clear to me on mention of +4/-10 line input switches.... they are there in the Pro because the line input bypasses the mic preamp in that model. So gain settings make no effect assuming you are using the correct frigging line input... so why are you using the wrong physical input to start with?

If you would prefer an Avid employee to ask you that question you can purchase a support ticket and contact Avid support.
Yeah, I'm already going way above and beyond with this thread, ha ha.

Ok, when I go back in there, I'll make sure that when set to +4 and when using a "1/4 TRS plug, the gain knob is bypassed.

I hope that's the case and that I'm just way off.

Thanks again.

-R
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