Why is the monitor meter reversed?
- Thread starter mbernardo
- Start date
Massive Master
www.massivemastering.com
That's *MINUS* 0 Decibels. Big difference.
Sorry I guess I wasn't clear on my question. OK, the monitor meter looks like this:
dB -114 -108 -102 -96 -90 -84 -78 -72 -66 -60 -54 -48 -42 -36 -30 -24 -18 -12 -6 0
Image: http://ccrma.stanford.edu/software/snd/snd/tutorial/images/jpg/1_01-ce2000.jpg
So when the audio is quiet, the reading is in the -114 and when loud, it is near the 0 (zero). Why is it set up that way? Wouldn't it make sense that if it is quiet, it is 0 (zero), and the louder it gets, the bar goes up to +12 or +50, etc?
-5
dB -114 -108 -102 -96 -90 -84 -78 -72 -66 -60 -54 -48 -42 -36 -30 -24 -18 -12 -6 0
Image: http://ccrma.stanford.edu/software/snd/snd/tutorial/images/jpg/1_01-ce2000.jpg
So when the audio is quiet, the reading is in the -114 and when loud, it is near the 0 (zero). Why is it set up that way? Wouldn't it make sense that if it is quiet, it is 0 (zero), and the louder it gets, the bar goes up to +12 or +50, etc?
-5
thajeremy said:
It's a perfectly sensible question in my opinion. I like people who ask rather than take things for granted and hope they can get away with being ignorant.
This is digital audio, and it's the convention (and a convention is all it is) to measure levels as a proportion of the maximum allowable. This is called 0dBFS (FS= Full Scale). As already said, our measurements are this are going to be negative numbers - less than 0. Another convention is to measure in Decibels. The Decibel or dB is intended to provide a measure of the difference between quanties of acoustic power. The actual unit is the Bel but this is more convenient to real sound levels in tenths of a Bel hence the decibel.
The way human hearing responds to level varies - progressively less sensitive as the level rises. So the Bel is a logarithmic unit to match this.
The formula for dB is 10log(a/b). The 10 changes the log result from Bels to Decibels. However, in our software, the correct formula is 20log(a/b).
Remember I said dB measures acoustic power? Well, the waveform in your software represents voltage levels that have been digitised - not power. Power is proportional to the square of Voltage (double the voltage and you quadruple the power), so to maintain the relationship between our digitised signal and the actual physical sound power it represents, we have to square the log which is done by simply doubling the 10, hence the 20log(a/b) formula given in apl's post, which is the one your audio software uses.
You probably know that the bandwidth of an audio signal is taken (another convention) between the low frequency that is -3dB below average and the highest frequency at -3dB. -3dB is chosen because it's Half Power - 10log1/2. If we used 10log instead of 20log for the signal displayed, we'd have to remember to use -6dB instead when measuring bandwidth and carrying out eq etc.
Of couse, the dB is normally used to measure a physical acoustic power level - SPL. In this case the dB value is related to a minimum reference power and increases above that in the expected fashion like most other measures.
This is digital audio, and it's the convention (and a convention is all it is) to measure levels as a proportion of the maximum allowable. This is called 0dBFS (FS= Full Scale). As already said, our measurements are this are going to be negative numbers - less than 0. Another convention is to measure in Decibels. The Decibel or dB is intended to provide a measure of the difference between quanties of acoustic power. The actual unit is the Bel but this is more convenient to real sound levels in tenths of a Bel hence the decibel.
The way human hearing responds to level varies - progressively less sensitive as the level rises. So the Bel is a logarithmic unit to match this.
The formula for dB is 10log(a/b). The 10 changes the log result from Bels to Decibels. However, in our software, the correct formula is 20log(a/b).
Remember I said dB measures acoustic power? Well, the waveform in your software represents voltage levels that have been digitised - not power. Power is proportional to the square of Voltage (double the voltage and you quadruple the power), so to maintain the relationship between our digitised signal and the actual physical sound power it represents, we have to square the log which is done by simply doubling the 10, hence the 20log(a/b) formula given in apl's post, which is the one your audio software uses.
You probably know that the bandwidth of an audio signal is taken (another convention) between the low frequency that is -3dB below average and the highest frequency at -3dB. -3dB is chosen because it's Half Power - 10log1/2. If we used 10log instead of 20log for the signal displayed, we'd have to remember to use -6dB instead when measuring bandwidth and carrying out eq etc.
Of couse, the dB is normally used to measure a physical acoustic power level - SPL. In this case the dB value is related to a minimum reference power and increases above that in the expected fashion like most other measures.
robbyrobmusik
New member
mbernardo said:
i was there man.. Its that way.. smaller number = louder..
Farview
Well-known member
They are negative numbers! When a number has a "-" in front of it, it is a number below zero. -20 is a smaller number that 10 (the difference is 30). -1 is a bigger number than -50. Welcome to 4th grade math.robbyrobmusik said:
Think of it as a countdown in a space shuttle launch, you are counting up to zero, you are not counting backwards.