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I've just noticed that the mixer we have in my church has both the main output level knob and sub main level in the back turned all the way to the right (at their max). Is this the default setting?

Strangely (to me at least) the max level for the main is +0 (printed on the back), while the max for the sub is +6. They both have -80 for the min. Why?

So, if I shoot for unity gain then I should leave the main as is (at +0) but turn down the sub a little bit? Hmm.... Why do they have to be different like this?

I think the current settings are bit too much for us that if we set the faders for mics near at unity gain and have the main out put at about 3/4 way to the unity from the bottom, then we have to turn down the pre amp level for the mics quite a bit, at around 10 dB. I think this is low because when I recorded a session last week (to a SD card with pre signal) the recordings had very low amplitudes. Also, when I checked the GEQ while the band was playing, the bars hardly moved at all at the bottom. Lastly, the line signal from the CD player is much louder than those of mics, that we have to keep the fader of the line in at about half.

So, I was wondering if we need to crank up the pre gain for our mics, but was afraid doing so may make them too loud. That's why I decided to check these output level controls in the back.

Any comments or suggestions will be highly appreciated!
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by SwitchBack on Fri Sep 22, 2017 8:51 pm
Hi and welcome,

That's a lot of questions in one post. I'll have a go at a few :)

The trim knobs on the back are for attenuating the analog output level to whatever input you want to connect to it. That may be a pro audio power amplifier but it could be the mic input of a video camera too. The scales are in dB so '0' means no attenuation (0dB) and '-80' means, well, an awful lot of attenuation. The '+6' for the mono output is because that output is the sum of the left and right outputs. With the same signal on left and right the mono output can be twice as loud (+6dB) as the left and right outputs.

Note that you still have to keep an eye on the mixer's output meters. When those meters go in the red then the audio will clip/distort, even with the trim knobs on the back turned way down.

As for the input levels: again, use the meters. Select the input (so that the signal shows on the meter in the FAT channel) and set a level you are confident will never go in the red. -12dB or even a few bars lower is usually a good area to be in.
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by johnpark5 on Sat Sep 23, 2017 6:01 am
Wow, so that's why sub main has +6 dB.

Then, I wondered why both main and sub main has the same minimum level at -80 dB. So, I searched the internet little bit and learned -80 dB is 1/10,000 while 2/10,000 would be like -77dB, so I guess it's close enough to be marked as -80 dB.

About the "proper" level setting of the trim knobs, I guess there are no predetermined fixed values for everyone,but just attenuate the output if it's too loud (for me), after setting the input and output levels at proper levels (so that they won't get into the red range), right?

I was kinda expecting that as an answer, but I still wanted to make sure I am not doing something stupid, or something which should only be done as a drastic measure or the last resort by adjusting these trim knobs. I am just an amateur/hobbyist who happens to have a great privilege of operating this cool mixer at my church :D I have much too learn.

Thank you so much for your response!!

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