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One reason the recordings sound fuller and rounder was the the use of compression, most often the RCA BA-6a Limiting Amplifier which was almost universal by 1952 or so. There were other including Gates and Fairchild but the RCA was the most popular and cheapest, so it ended up in broadcast and recording facilities. It is not hard to build a similar device but using modern parts....balanced line at that time was terminated 600 ohms and nominal +8 or 10 so signal output was high, but there was a built in balanced attenuator. It needed the high output to drive the dual diode 6H6 tube used to generate the control voltage for the variable Mu first balanced 6SK7 variable gain stage. There are more modern versions but the old metal tube 6SK7 is not hard to find, it was commonly used as AGC in receivers of the day.
Bandwidth was also very much limited on those recordings intentionally due to the limits of grove with cut masters(low frequencies were limited to increase track density...longer play time, and to avoid the tracking problems with high mass tone arms and needles following wide excursions) and high frequencies were limited because of broadcast limits and distortion with the high cutting angular velocities needed for the boost called for in any of the phono equalization curves over the years. RIAA called for 20db boost at 20khz at the cutting head. So to recreate that great old sound you just have to think of how the technology of the recording and playback gear impacted signal processing requirements. Vocals just sounded richer and fuller, and warmer by a combination of intent and by the technical needs of getting the content on the media of the day. I cut lots of albums with similar limiters, and oversaw each one as it was cut on the lathe for the final master.
Bandwidth was also very much limited on those recordings intentionally due to the limits of grove with cut masters(low frequencies were limited to increase track density...longer play time, and to avoid the tracking problems with high mass tone arms and needles following wide excursions) and high frequencies were limited because of broadcast limits and distortion with the high cutting angular velocities needed for the boost called for in any of the phono equalization curves over the years. RIAA called for 20db boost at 20khz at the cutting head. So to recreate that great old sound you just have to think of how the technology of the recording and playback gear impacted signal processing requirements. Vocals just sounded richer and fuller, and warmer by a combination of intent and by the technical needs of getting the content on the media of the day. I cut lots of albums with similar limiters, and oversaw each one as it was cut on the lathe for the final master.
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