Usually the signal will GAIN level differentiation: higher dynamic range, the quiet parts will become quieter relative to the peaks.
Remember, the above graph is time invariant, just showing overall energy per frequency.
For example, take a typically heavily compressed modern rock recording, looks like this. It measures DR6:
View attachment 32625
Now reduce bass levels by applying a high pass filter, 6 dB / octave starting at 300 Hz. Now the waveform looks like this -- note it has significantly better dynamic range. It now measures DR9 -- even though all we did was reduce bass levels (which you'd have to do to cut it to LP).
View attachment 32626
For comparison, if you apply a low pass filter to the original, 6 dB / octave starting at 2 kHz, the waveform looks essentially the same, and it still measures the same DR6.
In short: when you
reduce the amount of bass, it typically
increases dynamic range. Especially when starting with dynamically compressed bass-heavy music (most rock/pop). That's usually why LPs measure slightly better dynamic range -- because they had to reduce the amount of bass in order to cut the LP. Which often makes it sound better, since so many modern recordings have artificially boosted bass.