Why is the monitor meter reversed?

[mbernardo]

Newbie question: Why is the monitor meter reversed so that the peak is 0 decibels?

[thajeremy]

wow....

um...dude....

ITS SUPPOSED TO BE THAT WAY!!!

[Massive Master]

That's *MINUS* 0 Decibels. Big difference.

[thajeremy]

Originally Posted by Massive Master

That's *MINUS* 0 Decibels. Big difference.

yea...sorry I didnt catch that part....I was in such shock from the question in the first place...

[mbernardo]

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/s..._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

Originally Posted by thajeremy

yea...sorry I didnt catch that part....I was in such shock from the question in the first place...

[apl]

It the logarithmic ratio of the signal compared to the max allowable signal.

20 × log10(signal/max)

When you've used all your available signal you get 0. If your using 1/10 of your max, you get -20.

[Jim Y]

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.

[robbyrobmusik]

Originally Posted by mbernardo

Newbie question: Why is the monitor meter reversed so that the peak is 0 decibels?

i was there man.. Its that way.. smaller number = louder..

[thajeremy]

Iv been out of town for a couple of days.....Ill refer you all back to my original answer......

Originally Posted by thajeremy

wow....

um...dude....

ITS SUPPOSED TO BE THAT WAY!!!

[Farview]

Originally Posted by robbyrobmusik

i was there man.. Its that way.. smaller number = louder..

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.


Think of it as a countdown in a space shuttle launch, you are counting up to zero, you are not counting backwards.