Gain staging questions

Posted: Wed Aug 20, 2008 11:19 am

In my ongoing efforts of being a student of the Audio Engineering experience, I frequently find myself tweaking different areas of my gain structure. One aspect in particular has me a bit confused, so any advice or enlightenment that someone can throw my way would be greatly appreciated.

First, a little background:
The components of my signal chain are very straight forward..

Source (guitar/vox/bass)>Mic (where applicable)>Preamp>Audio Interface (RME FF800)>DAW (Logic).

I usually start by working from the SOURCE to the DAW and then adjust or experiment accordingly once I have things in order. How loud is my amp going to be, am I singing soft or loud, how much 'color' do I want from the preamp, etc...the basic stuff.

My main question lies with my RME800. I typically leave the input levels (faders in Total Mix) pulled all the way DOWN on the FF and just work with my input/output levels on my preamps and in Logic. If I raise the input in the RME I can hear an audible difference when monitoring, but not so much once I record and playback.

I guess I could sum it up by saying that adjusting the input level on my RME seems to do little or nothing with respect to whatever I may be recording. This leads me to wonder if I'm in fact doing something wrong, or maybe even have things setup incorrectly.

It's not to say that I haven't been able to get some really nice tracks recorded (I'm not complaining)...I just want to be certain that I understand better the 'what's and why's' about my signal chain better than I do.

Thank you in advanced.

Posted: Thu Aug 21, 2008 3:43 am

I think you are trying to make this more complicated than it need be, although you are right in thinking that an understanding of gain staging is crucial to getting the best out of your recordings.

First of all, make sure you are feedng your pre-amp outputs into the rear line inputs 1-8 of the FF800. Then use the FF800 software control panel to set the rear inputs to "Lo Gain". This gives you a nominal +4dBu level with a full scale of +19dBu, i.e. 15dB of headroom above nominal. Using the rear line inputs by-passes the FF800 pre-amps and so there is no other gain adjustment to do on the FF800.

Then simply adjust your pre-amp gain to give you correct levels. I would suggest peaking at around -6dBFS (+13dBu) as seen on your computer after digitization by the FF800. What pre-amps are they, by the way?

Posted: Thu Aug 21, 2008 8:46 am

Ok, so I do think I'm a bit off of the mark. I admit, the FF is a very complex piece of gear and much of it is over my head, but I don't mind taking some lumps while I learn.

So, I've actually been setting the input/output to +4dBu, not Lo Gain. My preamps are an ME1-NV, LA610 and a 737sp. The preamps all have +4 output, so would I not want to keep that consistent with the input on the FF800?

Thank you.

Posted: Thu Aug 21, 2008 8:50 am

....from the FF800 manual...

With +4 dBu selected, the according headroom meets the latest EBU recommendations for
Broadcast usage. At -10 dBV a headroom of 12 dB is common practice, each mixing desk operating
at -10 dBV is able to send and receive much higher levels. Lo Gain is best suited for
professional users who prefer to work balanced and at highest levels. Lo Gain provides 15 dB
headroom at +4 dBu nominal level.

Yep, that one got by me.
Very Happy

Though, I'm still not 100% sure about the input levels on the FF800. Am I still better off just keeping them all the way DOWN?

Thanks

Posted: Fri Aug 22, 2008 10:07 am

As I said previously, if you use the rear line inputs on the FF800 and set the sensitivity to Lo Gain, there are no further adjustments to do on the FF800. Look at the block diagram - the input level trim controls have no effect because they operate on the front panel inputs not the rear panel line inputs. You want to keep the faders all the way down to avoid any noise from open-circuit inputs getting into your monitor mix, although this will not affect the recorded channels.

Ignore the bits in the FF800 manual that talk about "broadcast usage". Pay attention to the bit about "professional users".

Posted: Fri Aug 22, 2008 11:51 am

Yep, got it. It took a couple of tweaks and re-reads but it makes sense now. I do use the rear line inputs.
I think it was more a matter of the FF being able to do so much more than I was utilizing...so surely I must be wrong, right? Not so much.

I like the KISS approach much better anyway.

Thanks for taking the time to help Boz.

This topic sponsored by: