Think of "0 dB" on your AV receiver's volume display as a kind of "maximum loudness" setting beyond which you may drive the amplifier into audible distortion or "clipping."
A receiver that does not use the relative volume display but instead uses the absolute display (eg., 0 - 100) also has a point beyond which you may drive the amplifier into audible clipping so that does not explain the purpose of using the relative display. The best point to take away from the article is the volume scale is dB accurate,
after you calibrate to a known level and only then can you compare two receivers for relative loudness.
'0 dB' is a convenient
reference point. The concept behind '0 VU' in the article explains the idea of a reference - everything else is relative to that reference. In the case of calibrating a HT receiver, the reference is a defined output Sound Pressure Level (SPL).
Here's how it relates to digital audio:
- Digital audio PEAKS at 0 dB, which means the sample value is all 1's. Lower levels are below 0 dB and represented by negative numbers.
- The 'reference' level most people calibrate to is Dolby Reference Level which is 105 dB. So in relation to digital audio, when the sample value on the recording is 0 dB, you want the SPL at your seat to be 105 dB.
- When you calibrate, you use pink noise at a defined level below 0 dB. The receiver test tones are at -30 dB. When you play the test tones and adjust the channel trims (with the master volume set to 0 dB), you want a reading of 75 dB (75 + 30 = 105).
So...with the master volume at zero, you get 75 dB when the input level is -30 dB. When the input level of the digital audio peaks at 0 dB, you get 105 dB. 0 dB audio sample level and 0 dB volume display == the reference level you were looking for.
Now, when the volume display is in the negative numbers, the SPL is
less than the reference level. It is convenient because it directly reads how many dB below the reference level is the output SPL. If you calibrated to Dolby Reference Level and are listening with the volume display reading -10 dB, the peaks will now be 95 dB and not 105 dB.
If you are playing something that has an
average level greater than the -30 dB test tones you used to do the calibration, it will be MUCH louder at the same numbers on the receiver's volume display.
