Roughly it is also the loudness of the loudest peaks in the song, divided by the loudness of the most silent parts. It is however far less obvious to provide a strict definition of the dynamic range of a recording than for a recording medium. Evidently it cannot exceed the dynamic range of the medium it was recorded on. Similarly, the dynamic range of a piece of music can also be defined. Yet, even when taking large error margins into account for this, it is obvious that the 96dB dynamic range of 16-bit audio is plenty for consumer audio.
Mind that I am mixing dB(A) and dB here, which is not exact science. All the CD did was increase the margin, cater for perfectly silent environments, and of course avoid the gradual degradation of an analog medium. This explains why the 70dB of vinyl records was adequate. In practice, any realistic ‘silent’ environment will have a background noise level of about 30dB(A). Human hearing ranges from 0dB(A) to 120dB(A), but anything above 100dB(A) is to be avoided because it will cause permanent hearing damage. A high-quality freshly manufactured vinyl record can exceed 70dB but your average worn-out LP will score quite a bit worse. For 16-bit digital audio (such as the CD or decoded MP3 audio) this is 96dB. The dynamic range of a recording medium is defined as the highest amplitude it can represent, divided by the smallest amplitude it can (reliably) represent. The actual reason why two recordings that employ the same range of values on the same medium can differ in perceived loudness, will be explained further on. So you might be thinking that louder songs just go higher in these numbers, but this is incorrect: every well-mastered song will use (almost) the entire range that can be represented by 16-bit numbers.
Digital audio is most commonly represented as 16-bit numbers, and these numbers can only represent a limited set of values.
The maximum amplitude of recorded sound waves is limited, either by the physical properties of the recording medium or by the digital representation.
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