Input gain and preamp
 

Hi

How do I know what my input gain should be set to? I have Sound Devices Mixpre-3. I know where to set it I just don't know what I need to set it to.
Also, I have fethead preamp attached to the mic. It gives me extra 18db, but I hear shhhhhh sound coming from it in my headphones before I even connect the mic. Is this normal?

Re: Input gain and preamp
 

The convention in digital recording is to set the gain so the signal averages around -18 dBFS (or some other value near that number, depending on the converters). That means it's spending about half the time above and half the time below that value when the source is in its normal/loud volume range.

Typically, a 0 VU level will translate to +4 dBu, which lines up to -18 dBFS for many converters, but sometimes a slightly different value. The exact number isn't critical as long as the analog side of things is in its optimum range (above noise, below distortion) and the digital level is well below 0 dBFS.

Percussive sources are a special case since they have so little sustained energy. For those, you have to set it by peak level, being sure to stay well below 0 dBFS. Peaks at -6 dBFS are okay if you're reasonably sure it's not going to go higher, but you can keep the peaks at -12 dBFS if you want a bit of safety margin.

Note that a signal recorded with an average level of -18 dBFS will sound low compared to finished audio. That's normal. The final levels for delivery should be achieved in post.

I'm not sure about the noise you're getting from the Fethead/preamp. I'd say don't use the Fethead unless you really need to to get a mic's signal up to the required level.

Re: Input gain and preamp
 

A very simple answer set gain so you're peaking -18db to -6db with fader at 12 position. This allows plenty of headroom so you won't clip. In post you can adjust it to your liking. The amount of headroom varies based on what you are recording. All of this assumes you have proper mic to subject distance. If you have a dynamic mic 6ft away then increasing the gain to achieve proper levels, you'll end up with a lot of noise.

Re: Input gain and preamp
 

If the MixPre has enough gain, (which it should in most scenarios), do not use the fethead preamp. If you are recording at conservative levels, use 24 bit depth .. or .. 32 bits if you have the MixPre II, and you will not have to worry about digital clipping either.

Re: Input gain and preamp
 

Thank you all. I will remove the fethead

Re: Input gain and preamp
 

Can you explain more how to do this? What do you mean by fader at 12 position? Here is a photo of my recorder. What should the fader be set to on my recorder?

Re: Input gain and preamp
 

12 (o'clock) on a channel fader is usually "unity gain", unless specified or marked otherwise..

Re: Input gain and preamp
 

So set it to roughly where the number 1 is written and then adjust the input gain?

Re: Input gain and preamp
 

Yes. When the fader is in the middle (12 o'clock) you have room to adjust the levels up or down while recording.

Re: Input gain and preamp
 

Do I need to be speaking to the mic while I'm setting the input gain?
I watched this video and I can't tell if he is talking to the mic or not:

Re: Input gain and preamp
 

It is better to have the talent speaking in a way that simulates the coming live shoot to get the most accurate levels.

If no one is speaking there is no way to set the levels meaningfully.

Re: Input gain and preamp
 

I'm not talking about just setting levels. Obviously someone has to speak. I'm asking when setting the channel input gain.

Re: Input gain and preamp
 

Like I said before the fader should be left at the 12 o'clock position, while you set your levels by adjusting the gain. Gain adjustments are done before recording when you do your audio check.

Re: Input gain and preamp
 

Hi Kathy. There’s a lot of good help here and my 2 cents is, you should go back to the start and follow the UTube video introductions for your MixPre 3.

I didn’t post any here because I think the secret is to keep looking for the videos that answer all your questions, if one is confusing don’t worry just move on. It can be frustrating I know, but take it slow we all started like this. Keep your mixer with you and try what’s suggested, make notes, you’ll get there.

Cheers.

Re: Input gain and preamp
 

Yeah if you're unfamiliar with audio and are a visual person it might be easier to watch mixpre video tutorials.