What does 0db -5db mean when setting your amp gain?

A Gain In setting of 0dB means that for a signal that is coming in from a device which also produces a +24dBu maximum level no correction offset is being applied to match the gain structures
support.biamp....
I found this awesome write up by maestro2005
Decibels are a relative scale. It's a bit like height/altitude: it doesn't make sense to say that you're "at 500 feet". 500 feet above what? The ground? Sea level? The center of the earth? There are certain contexts where a particular reference is assumed (building height is measured from the ground, mountain peaks are measured from sea level), but without that context or being explicit, the single number is meaningless.
Decibels are additionally tricky because they're a logarithmic scale. No matter where you are, +10dB is 10x the power, -10dB is 1/10th the power.
For processing elements in the middle of the signal chain, the reference point is usually the input. That is, 0dB of gain means the output is the same as the input. The reason 0dB is at different points is due to the nature of the equipment:
The threshold of a compressor is asking, "at what point below full volume do you want the compressor to kick in?", so 0 has to be the maximum value.
0 is in the middle of an equalizer, because frequency bands might be adjusted up or down, and 0 is the neutral "do nothing" point.
Faders on a mixer go from -infinity to +10 (usually). They're not designed to be used as amplifiers, and if you find that a channel is way too quiet you should fix that somewhere else in the signal chain. But they give you a little room just in case. So most of the operation that you should be doing is in the negative range, with 0 being full volume.
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[@paulsalas7079]

Finally an easy explanation, that is explained well...thank you soo much!!

[@CarAudioEnthusiasts]

Glad it was helpful!

[@grimtim1030]

That was awesome i thought i was gonna be confused but the way you described it made it easier to understand 😎🤘🏽

[@USDevil1775]

Thanks brother, I'm surprised more people aren't watching this and learning to adjust their gear, maybe they doing what I used to do, connect and go! Ha!

[@BappaOnyumbe]

Fantastic, thank you. But, a sine wave is a constant, and music is totally dynamic! So even if you set a fixed voltage for a speaker with a multimeter, and then listen to actual music and check out the voltage output on the multimeter, it will constanly change and the values will be a LOT lower than what you just set. Does the -5db test tone setting helps with "upping" the average actual output to the theoretical best? Even if it will clip at some high points..

[@hadbl12]

Thanks for the explanation. I never really knew what that meant

[@CarAudioEnthusiasts]

Np, took a bit of research to totally understand myself.

[@davpart7723]

Right on, thanks!!!

[@CarAudioEnthusiasts]

No problem!

[@BEAZY_5150]

What if you’re overpowering your subs RMS? Would you still tune to-5 to “get more power out of your amp”?

[@soundbycloud]

I'd say from experience tuning with the DD1+, tune subs to 0dB-3dB IF:
- Your amp/sub wattage isn't matched, as in amp rating > sub rating, because clipping when the amp is overpowered is worse than clipping when matched
Tune subs to -5dB IF:
- The wattage is matched and impedance rise is known
- You play rebassed music
- You'd like a bit more oompf out of your system
Tune subs to -10dB IF:
- The wattage again, is matched and impedance/box rise is known and calculated for
- You don't play rebasses, just regular music
- You have a good working nose haha, subs give off signals when they're being clipped.
Now for the mids and highs I usually tune to 0dB or -3dB on customer systems since that balances both clipping and loudness, as long as they keep the EQ as I've set them and only go in the negative section on the EQ and not positive, they'll be fine.
-5dB for mids and highs when the vehicle/system might compete.
Just my two cents, anyone can add or correct me if I said something wrong, just giving info that's worked for me.