Comment on Audio cable measurements are driving me crazy — why don’t they null?!?
Uebercomplicated@lemmy.ml 21 hours agoI’m not sure if you’re reading the graph correctly, this is the delta between two of the digital files from the video’s description. So a signal of -40 dBFS is quite audible, since it’s all relative to 0 dBFS (full scale).
And it isn’t the recording itself, it’s just the difference between two of the recordings provided in the video’s description. This is commonly known as a digital null-test, and let’s you find the amount (and significance) of difference between two digitally encoded recordings, and in particular at which frequencies those differences lie.
You can try doing it yourself by downloading the audio from the YouTube video’s description and then playing two of them at the same time in audacity, but with the phase inverterted for one of them. Just make sure the phase and volume are aligned. Then you can hear the difference between the recordings yourself!
The question is, where does this difference come from.
marcos@lemmy.world 21 hours ago
At -40, it doesn’t make any difference what kind of dB you are talking about.
(Well, if you are looking for superstrings evidence or even quantum gravity, it does, but I guess it’s not your case.)
bigpEE@lemmy.world 5 hours ago
It sounds like you think -40dB is such a small factor it must be inaudible. It absolutely is, the ear has like 100dB of dynamic range
Uebercomplicated@lemmy.ml 20 hours ago
en.wikipedia.org/wiki/DBFS
marcos@lemmy.world 20 hours ago
Relevant line:
That means the US definition you can’t hear anything below -24 dBFS. It’s the largest value there, it’s -18 for the EU.
Uebercomplicated@lemmy.ml 11 hours ago
BTW, you also seem to have misunderstood dBU. That is in voltage, which means the signal is amplified before you listen to it. I would highly recommend reading the wiki page on decibels: en.wikipedia.org/wiki/Decibel
I think there’s good YouTube videos on how decibels and digital audio work as well.
Uebercomplicated@lemmy.ml 11 hours ago
What you quote is for conversion with analog levels, which is not what’s happening here. Everything I’m doing is 24 bit digital audio, which has 144 dB of dynamic range. That is a little over-kill, which is why most audio files are distributed as 16 bit, so 96 dB. That means you can hear anything from 0 dBFS to -96 dBFS (with proper dithering). That is why the cutoff point in the graphs I showed you is -100 dBFS, since you realistically won’t be able to hear below that anyway (audiophiles disagree), in the final file.
-40 dBFS only represents how the signal is stored in the digital file. It has nothing to do with the signal’s actual volume. I play those -40 dbFS through my computer, then my DAC, which outputs at about 2 VRMS, into my pre-amp, which increases the voltage again, into my amp (which, again, increases the volume), and finally into my speakers, which output that -40 dBFS, which is now signal at about 70 dB SPL (actual volume).
dBU is for analog line-level, and the conversion you showed is what I would use when routing my console back into my computer. But analog line levels are still very audible at -40 dBU, usually, not that that’s relevant.
You have to understand that this is not real volume. It is just how the volume is stored digitally. If you have a -40 dBFS noise floor in your audio file, and the music has a 12 dB dynamic range peaking at -1 dBFS, you will hear the noise clearly throughout the entire track, because you are amplifying the entire thing greatly, since you are ultimately transforming this into dB SPL.