there is a difference there because there really isnt a reference level to speak of when you put a level on the chip or disc with an adjustable volume knob.
if it was all done in organized fashion, then there wouldnt be a volume knob on the receiver .. it would be a gain knob to get you at the reference level.
there isnt really a reference level either though.
because reference level is what lets 10,000 people listen to something and hear it exactly the same as if you were the microphone standing there listening.
it means the recording would need to be raised or boosted to meet the reference line.
it would help a tremendous deal to get in there and look at the compiler for the sample conversion, and then pick something as the reference 0dB to allow every single thing after that to go back to that 0dB
from amplifier's with 100 watts to amplifiers with 500 watts
to dvd's and blu-ray movies .. to concerts on disc .. to music on disc or computer file .. to preamps .. to turntables .. to speaker resistance.
i did say the reference doesnt exist ... but is it because of different sound levels you found, or is it because the audio track simply hasnt been loaded into a program that will tell you how loud or soft the audio is compared to the reference 0dB
anybody can go in there into the compiler and say what is 0dB
but that doesnt mean people will work together as a team and keep the same line used time after time again.
no matter how ugly things get..
when your listening room is setup, you will find out if the audio is working with the 'normal' reference 0dB or if it is using one of it's own.
sometimes they turn down an audio track below 0dB to get all of the dynamic peaks to fit into the digital domain.
if your limit is 110dB and you peaked at 112dB .. then simply turn it down 2dB and you get the full signal without over-processing the sound and ruining the raw content.
..and when that happens, it is up to you to bring the volume up 2dB
some people use pure decibel level
some use barometer pressure.
it helps to know what microphone was used to learn the relationship between barometer pressure and decibel level.
knowing the gap will help anybody dial in the reference level.
the hobby has shown once again that it is better to be aware.
and once again, they give us some tools to help ourselves remain stable.. specifically speaking about the reference 0dB
because if you dont believe one piece of software, you could try half a dozen audio analyzer programs and if they all say 0dB .. you could feel a bit more confident about what a reference level is.
if the receiver's test tone isnt at reference level.. it could simply be because they didnt engineer a circuit to boost the signal.
the signal probably comes as audio data on a chip sent to the digital to analog convertor? or did the chip send the audio to the amplifier on the side?
maybe they told you what the maximum volume level with the test signal.
maybe they told you more than the maximum.
maybe that maximum is what they recorded the total harmonic distortion number at .. and the volume is up higher than it ever needs to be, so turning it down gets you less distortion but it also turns down the dB level of the test tone.
my two guesses:
1. the chip sent the audio to the amplifier with less voltage .. less voltage = lower dB level
2. the chip is really cheap junk and couldnt hold a 0dB signal (kinda like saying the data on the chip wouldnt stay there at 0dB because the data would be corrupted .. so they used a lower dB to keep the data from corruption)
i've heard the test tone from my receiver and it doesnt even sound the same as the pink noise from a test disc or audio software.. and that is before noting anything about it being louder or quieter.