# Why is volume rated at 0 decibels?

1. May 6, 2008

### mordechai9

I got a Denon stereo receiver in this past year and I noticed that the volume meter starts at something like -70 decibels and moves up through 0 decibels. I've also noticed on other audio equipment that the 0 decibel rating is linked to some kind of amplifier power level or something. Why is the volume rating like this?

2. May 6, 2008

### Howers

Because engineers want to feel unique by complicating things. Its all relative.

3. May 6, 2008

### f95toli

Because our hearing is roughly logarithmic, not linear. It therefore makes sense to use a logarithmic scale, it also why the potentiometer inside the amp is logarithmic.
Moreover, dB is usually easier to use than a linear scale since you can just add/subtract the numbers when you e.g. want to calculate sound pressure levels..
-70 dB simply means that the potentiometer is attenuating the output signal by 70 dB.

Hence, there are plenty of good reasons

4. May 6, 2008

### mordechai9

Yea, that's pretty much what I figured, but I don't understand why -70 dB corresponds to silence. Why is it "attenuating the output signal by 70 dB"? Is there something significant about the 0 dB level in this setting?

5. May 6, 2008

### f95toli

0 dB on a linear scale is 1 (10^0=1), i.e. attenuating a signal by 0 dB is the same thing as dividing it by 1.

Edit: And -70 dB is not silence, it is just very quiet. HOW quiet depends on the power of your amp, the sensitivity of you speakers (rated in dB/Watt) and how far away you are.

6. May 6, 2008

### Gokul43201

Staff Emeritus
I think I've seen it the other way round on some receivers, going from 0dB up through positive numbers. Maybe different receivers spec signal strength at different stages - some after the final amplification stage and some before?

If I recall correctly , the textbook definition of sound power levels (albeit, the high school definition) sets the 0 at the threshold of hearing (Intensity around 10^-12 W/m^2).

Last edited: May 6, 2008
7. May 6, 2008

### BobG

It actually makes a little sense. At 0 dB, the receiver is outputting the maximum amplification that it can put out without distorting the signal. You then attenuate the signal since that's easier to do without distortion.

If you're going from 0 dB to 70 dB, then 0 dB presumably means no amplification on the final stage, while 70 means maximum amplification (without distorting the signal?).

Of course, regardless of what they're actually doing, they could just as easily put anything on the scale: 0 to 10 (with 10 being loudest); 0 to 17 (with 17 being loudest); they could describe it in words (quiet, medium, loud, really loud, etc). You're going to adjust the volume to whatever sounds best regardless of the scale they use.

Last edited: May 6, 2008