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Thread: cumulative volume of tracks

  1. #11
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    Actually, you get a 6dB rise every time you double channel count of identical signals. For different signals it's approximately 3dB per doubling.
    Last edited by bouldersoundguy; 10-01-2019 at 13:21.

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    Cubase can do the same thing if you aren't quite up on the pathways - the input channel is on the output, plus the track where it's going, and if you've got effects running, then they too add to the apparent volume. Mind you, so did my old analogue desks when you were tracking with groups to split the outputs to the record outputs.

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    Quote Originally Posted by bouldersoundguy View Post
    Actually, you get a 6dB rise every time you double channel count of identical signals. For different signals it's approximately 3dB per doubling.
    I've always sucked at this math, but doesn't that depend on how your meters are configured?

    It's, what? 3 dB is double the voltage; 6 dB is double the physical power coming out of the speakers, and 10 dB is double the perceived volume, right?

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    Quote Originally Posted by VomitHatSteve View Post
    I've always sucked at this math, but doesn't that depend on how your meters are configured?

    It's, what? 3 dB is double the voltage; 6 dB is double the physical power coming out of the speakers, and 10 dB is double the perceived volume, right?
    I believe it's the other way around from what you said, doubling voltage is +6dB while doubling power is +3dB. That's why doubling channel count for identical signal is +6dB. But in the real world you don't have a bunch of tracks of the same signal, you have signals that are non-correlated. They add in a more random way, so doubling track count to the master bus is approximated as +3dB. This also explains pan law, because in voltage terms perfect summing between left and right speakers would give you +6dB, but acoustic summing is never perfect so it's approximated to something like 3dB, with the center position being at -3dB compared to fully panned. Other common pan laws are 2.5dB and 4dB.

    Audio meters are generally measuring voltage (except for dBFS, which is measuring a correlation of voltage, which is probably why 1 bit represents 6dB). I think many meters on amplifiers measure power.

    Doubling the watts of an amplifier allows it to put out +3dBSPL because SPL is a power measurement. But you can't assume just switching out an amp for one with twice the wattage will give you +3dB because it may not have the internal gain to do it automatically. You might have to feed it with more input voltage. Boundary effect is also a power effect. Each time you add a boundary you get a 3dB boost at lower frequencies (below 100-300Hz, depending on circumstances).

    I can't remember if 10dB (1 bel) of power or voltage is a 2:1 perceived difference. I suspect it's power.

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    [B]ouldersound Guy,

    Although it was a VERY long time ago, when at Uni we were taught audio in valve language, I am sure that I was taught that if you added two identical audio signals (ie voltage), that the level would rise by +3db and that doubling the output power on a loudspeaker was a +6db increase in volume (ie SPL).

    I will have to either do a test on one of my old analogue consoles, that has analogue Vu metering or dig out my now VERY dusty Uni books to be sure.

    Talking of being taught in valve language and to give you an idea of the era (!!!!!) --- or is that showing how old I am !!!!!

    One night the lecturer entered the lecture theatre and proceeded to say "if anyone has anything that is super urgent that needs doing tonight, I will not be annoyed if you leave, as tonight's lecture will not be part of the exam, but I have to give the lecture all the same" to which he put his hand in his pocket and pulled out a transistor and showed it to the class stating "this is what is called a semi-conductor device, but do not be to concerned as it will never take off" !!!!!!!!!

    David

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    Quote Originally Posted by bouldersoundguy View Post
    Actually, you get a 6dB rise every time you double channel count of identical signals. For different signals it's approximately 3dB per doubling.
    Yes and if we stick to voltages, two summed "correlated" sources such as sine tones of equal amplitude will result in a 6dB higher level (look up the basics of summing op amps)
    The same goes for two identical music sources, though why one would use up an extra track for that I cannot say?

    Uncorrelated sources such as resistor noise add as a 3dB voltage increase. If you simply mono a true stereo source, CO-I say you get a signal inbetween the two limits.

    The remarkable result of all this is that you can make a MUCH quieter balanced line input using 8 op amp per ch than with one!

    Dave.

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