The caption says that the right is analog, left is digital. Wikipedia says that digital still has headroom because the "0" (nominal level) is not whatever loudest peak is hit during a song. There's also various standards with different nominal levels: https://en.wikipedia.org/wiki/Headroom_(audio_signal_processing) I would assume that audio is similar to photography: in which a digital medium is still reliant on an analog to digital converter, and then ultimately the digital to analog converter used in playback. With photography, a RAW file records all sensor data: going down to the noise floor and highest saturation point. Digital cameras can record a higher dynamic range than displays and print have been able to reproduce: so you can optimize contrast through adjusting contrast curves (or tone mapping). To create a rendered image, they also pick the black point and white point in the tonal scale (and each camera brand has different values: some have cleaner ADCs and can have a lower black point, while others try to have higher saturation). I can imagine how much more complicated things get when you have a recording system that is also dependent on time: when there can be swings in dynamic range.