I’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.
Uebercomplicated@lemmy.ml 1 day ago
I realize I may have left out something key to understanding dBFS for the unfamiliar. Unlike with dB SPL, which is what you are referring to with “at audible 0dB,” zero dB refers to the loudest possible sound in dBFS. The unit stands for decibel relative to full scale, where full scale (loudest possible sound) is 0 dB. So in dBFS, unlike with dB SPL (sound pressure level), all audible sound is stored as a negative dB value. When you listen to the audio file, this is first converted to a voltage, and then to sound pressure, which is finally measured in positive dB SPL.
If that doesn’t explain it for you, I don’t know what you don’t understand, and I can’t help. I would recommend finding some YouTube videos on the subject, in case you’re a visual learner.