Unique Challenges in Rare Paramount Records Blues Discs
Although major label 78rpm records are remarkably free of production flaws and technical cutting errors, this is not the case with budget labels like Paramount and Gennett. In the quest to increase the transfer quality of these discs with poor technical specs but incredible content, we are constantly investigating the causes of the sound quality limitations and how to best overcome them.
One example of a technical issue we occasionally find is varying groove depth due to poor flatness of the master wax blanks used during recording. This was likely either caused by poor shaving of the wax blanks, or by poor flatness of the recording lathe turntable itself. Poor flatness alone is not the full problem, though. In the higher-quality Western Electric recording heads used by Columbia, Victor, Okeh, HMV, etc, a sapphire advance-ball was used to help the head maintain a consistent groove depth in the wax. Without an advance-ball, though, any error in flatness across the disc can result in a change in groove depth.
Although some groove depth change is to be expected in records cut with lower-end recording systems, the severity of the problem found in some of the discs is almost unbelievable. For example, the groove depth can occasionally even double within a single revolution. A video of this cyclical groove depth change is shown above.
It is important to note that in discs with this problem, the flatness of the record surface is largely irrelevant since the stylus is moving inside the groove rather than on the surface of the record. Additionally, the problem becomes increasingly severe when the records were played back on original vintage equipment. When acoustic reproducers with steel needles were used, the heavy tracking pressure prevented the needle from following the depth changes resulting in severe cyclical groove damage as the needle digs into the thinning groove.
With these types of varying depth records, the disc transfer setup becomes even more critical. Not only does stylus selection because more touchy, but record centering and shimming also become increasingly important. Although it is not always possible to remove the noise modulation entirely, with very careful setup it can be reduced greatly and the records made much more enjoyable.