acoustic vs. electronic

I recently bought a 2CD set of Bellini opera arias. Those before 1925 are on one and labelled acoustic, those of a later vintage(1925-1949) on the second CD are labelled electronic. My guess is it has to do with the microphone recording the various artists. Am I right? Any replies appreciated.
I think that the ones before 1925 could have been recorded on an Edison wax cylinder, cutting them by using a stylus driven only by mechano-acoustic power amplified by focusing sound waves using those big metal horns. After 1925, electronic amplification was available. Call this an educated guess...I may be wrong
probably right based on the sound quality, thanks
Yeah, it should have a lot of static and noise, and have
no bottom or top end, with very limited dynamic range.
It was long believed that those early (pre-electronic) recordings had "a lot of static and noise, and no bottom or top end, with very limited dynamic range". In recent years it has been discovered, through digital conversion and analysis, that high and low frequencies are actually present, though greatly attenuated, and the noise can be modeled and removed. I have heard restored recordings that are nearly a hundred years old which sound like they were made in the 1950's.