on a sub channel at 0db test tone i would turn the gain to the point of roughly 10% clipping. or to say that i would set gain until i start to see a small trace of square at the top. check VA and calculate 10% over that.  for a mid or tweet i would stop turning the gains up as soon as i see the peaks going flat.

 

in a sub i care its clipped due to thermal capacitance issues, burning up a coil or such. on mids or tweets i would worry about distortion in music 

I normalized my entire music library for my car to -5db's using Platinum Notes and used -5db test tone and bought the DSO 112A and some better leads for $70. Worked out great. That way I had a more predominant means to prevent clipping than using my 41 year old ears, especially if I ever decided to indulge in Bandpass for kicks.

I also went to a website that tests your hearing so I can make a make a graph to illustrate where my hearing starts to roll off and which frequencies that I perceived as being the loudest or to say that I'm most sensitive to. I think that plays a big role in ones audio bias. After I measured my car's acoustics I focused more on the frequencies I'm most sensitive to using my DSP and adjusted frequencies I'm least sensitive to and cut off the ones I can't hear anyway....then I readjusted my gains since I had to raise a number of frequencies.

That helped tremendously for me fine tuning a sound signature that I prefer the most. A lot of audio knobs like to talk about how they only want to hear it as the artist intended..etc imo is nonsense when you consider that a lot of audio engineers in the studio don't have golden ears, some aren't very good at their job and how much $ a studio wants to invest is a major part of how the end result is going to be. That plus given the environment of a vehicle is why I personally process all my music to make it easier to have my entire collection cater to my individual taste. 

7 hours ago, ncc74656 said:

on a sub channel at 0db test tone i would turn the gain to the point of roughly 10% clipping. or to say that i would set gain until i start to see a small trace of square at the top. check VA and calculate 10% over that.  for a mid or tweet i would stop turning the gains up as soon as i see the peaks going flat.

 

in a sub i care its clipped due to thermal capacitance issues, burning up a coil or such. on mids or tweets i would worry about distortion in music 

 What do you do when the sound levels do not match once you have set all your amps to an arbitrary setting with a scope?

this depends on services they bought, if they paid for o scope tuning alone then it sits where it sits, unless there is a major noticeable deviation then we turn down what ever is too loud. if they paid for rta tuning then we go through and do a tune to setup staging and such but this can only be sold with a dsp.