http://www.audiomisc.co.uk/HFN/HDCD/Enigma.html
https://en.wikipedia.org/wiki/Compac..._Digital_Audio
It's possible he's right. CD's aren't strictly LPCM, they have a variable gain control.
Quote:
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Some CDs are mastered with pre-emphasis, an artificial boost of high audio frequencies. The pre-emphasis improves the apparent signal-to-noise ratio by making better use of the channel's dynamic range. On playback, the player applies a de-emphasis filter to restore the frequency response curve to an overall flat one. Pre-emphasis time constants are 50µs and 15µs (9.49 dB boost at 20kHz), and a binary flag in the disc subcode instructs the player to apply de-emphasis filtering if appropriate. Playback of such discs in a computer or 'ripping' to wave files typically does not take into account the pre-emphasis, so such files play back with a distorted frequency response.[
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