Command Performance - 1942 (shows 78s being made)

[gregbogantz]

Jim has it essentially correct. "Living Stereo" was simply a sales term used to introduce the new stereo recordings by RCA. All the early RCA stereo releases for several years were marked as Living Stereo. CBS had their "360 Sound" in their latter mono days, which became "Stereo 360 Sound" with the advent of stereo. Other labels coined their own buzz words to describe the new system. Other than being stereo, it was nothing special.

I'm sure we discussed the RCA "Dynagroove" process here on some earlier thread, but I can't get the archive search to turn it up. Also covered then was the "Dynaflex" record profile which was introduced about the same time. I don't think RCA issued Dynagroove recordings outside the USA. The reason mostly was due to the fact that the Dynagroove process required an analog computer (remember, this was 1963 - before digital microprocessors) to predistort the waveform just as it was delivered to the cutter head at the mastering site. This analog computer equipment was known as the "dynamic recording correlator" or DRC. The device was based on research done at the David Sarnoff Research Center which was the central research unit of RCA Corporation. Several technical papers about it have been published in the Journal of the Audio Engineering Society, and you can find those papers in some major libraries as well as at the AES online site. Most of the RCA cutting locations in the USA were equipped with a DRC to perform the compensation during mastering. Some tape recordings of the predistorted signal were made as backups and to allow recuts in studios that did not have a DRC, but I'm not sure they were used for any international releases, so you euro guys may not have heard about it on the other side of the pond.

Yes, the system was designed to compensate for the scanning loss or tracing distortion caused by playing a record with a rounded stylus which is cut by a sharp edged stylus. This problem occurs most noticeably with the vertical component of analog records. Early audiophiles complained LOUDLY about how distorted the early stereo records were compared with the mono equivalents. They were correct. And the reason is that tracing distortion occurs in all analog records but is mostly mechanically cancelled out in pure lateral recordings. Stereo records have half their signal derived from vertical modulation (and half from lateral), so all the distortion that occurs from tracing problems shows up in BOTH channels of a stereo record playback. The problem is made worse when the radius of the playback stylus is larger. Early stereo pickups used the same 1.0 mil spherical stylus as was used for mono microgroove records. This produced considerable distortion when used in stereo. The first attempt at helping this problem was the introduction of the 0.7 mil conical stylus. Some cartridge makers even offered 0.6 (Shure) and even as small as 0.4 mil (the ADC Point Four model) conical styli. This made a fair improvement, and 0.7 mil is the size that is still used today for less expensive stereo pickups. But the tracing distortion was still evident. The DRC predistorted the waveform sent to the cutter with antiphase distortion such that when combined with the tracing distortion produced by a 0.7 mil stylus, the predistortion would cancel with the playback distortion.

The system actually worked, but not as well as it could have for several reasons. The main problem was that the stereo cutters of the day (early 1960s), primarily the Westrex 3C and 3D models had insufficient bandwidth to pass all the supersonic distortion products produced by the DRC. Consequently, the predistortion was not accurately recorded by the record cutter and so it wasn't there to cancel out with the playback distortion. The second problem with the DRC was that it was unstable. I had one at the RCA Records lab when I was in Indy, and I fiddled enough with it to know that it was difficult to keep in tune. As Jim says, the elliptical stylus was re-introduced about this same time, and the sharper scanning radius of that stylus shape helped to reduce tracing distortion. I say "re-introduced" because Edison had actually invented the elliptical stylus back around 1902 when he came up with the "doorknob" shaped stylus for playing his 2-minute wax cylinders. Everything old is new again, even though the elliptical stylus was hailed high and low as being a brand new "breakthrough". Nope. Edison did it first. Anyway, the average record user was oblivious to the tracing distortion problems because they were playing mostly scratched-up records slathered with peanut butter and beer. "Distortion?, What's distortion? Crack me another Bud." And with most audiophiles adopting the elliptical stylus (and the later Shibata and other line-contact shapes which are even better), the need for the DRC essentially went away.

Interestingly, the DRC was revived by JVC when they brought out the CD-4 quadraphonic disc system. Tracing distortion of the baseband signal resulted in intermodulation distortion (IM) of the carrier signal, even when a Shibata stylus was used. So the JVC CD-4 cutting systems included a circuit they called "Neutrex" which was optimized for the Shibata playback stylus. This was the DRC re-invented. In their later cutting systems (Mark II and Mark III) they included the DRC, calling it the Neutrex-I and they also included a Neutrex-II which was predistortion of the carrier modulation to compensate for the IM caused by the tracing distortion of the baseband signal which was not fully corrected by the Neutrex-I. The DRC worked better in this case because the predistortion was relatively little for the Shibata stylus compared with what RCA had needed for the 0.7 mil conicals. And the newer Neumann and Ortofon cutting heads used to master CD-4 records had MUCH better bandwidth than the old Westrex cutters, so all the predistortion was accurately cut into the record. CD-4 cutting was also done at ½.7 or ½ speed which further increased the bandwidth of the signal layed down on disc. You audiophile types might find it interesting to play some CD-4 records just in stereo. With a Shibata stylus, the ordinary stereo playback (disregarding the carrier information) is VERY clean - probably the cleanest analog disc reproduction by a playback stylus that you will ever hear.

[recordo]

Greg, many thanks for that info!

I seem to remember having Dynagroove Reader's Digest records here in Australia years ago?

thanks again Greg!

[gregbogantz]

Recordo, it could very well be that Dynagroove Reader's Digest records were available in Oz. With a few exceptions, most of the Reader's selections were from RCA artists and those records were cut and pressed by RCA. RCA had a pressing plant somewhere in Oz to serve that country's market, but I can't remember in what city.

[Lenoirstreetguy]

Greg, I figured you would have had hands on experience with the Dynagroove process and so I was fascinated to read your reply. I always had the feeling that something wasn't right with the Dynagroove stuff ..especially in the early days, and the difficulties with the Westrex cutter's frequency response solves that mystery!! I mean, RCA really did push the process. Did RCA apply differing amounts of correction to different records , because some of them sounded ....as I recall...quite acceptable and others did not.

Jim