Some time back I reported hearing the first disc recordings commercially released by the audio company known as "dbx." The records were cut from original master tapes via a "coding" process that compressed the original dynamic range of the master tapes. For playback, the disc had to be "decoded" so that the dynamic range was restored. Any of several dbx devices (offered originally for tape-recording) could do the decoding; the unit offered for disc playback in particular was the model 21, priced at $109. It is patched into the stereo system between preamp and power amp, or into the tape-monitor facility.

The company has released four new albums containing symphonic music whose internal textures demand the purest kind of recording. I also have updated my system with a new Yamaha model YP-D71 turntable, a rock-solid unit that seems impervious to the acoustic "shock effects" of the dbx discs when played at loud volumes on less substantial turntables.

If anything, the audible results are even more outstanding with the new dbx releases ("A Slavonic Festival," St. Louis Symphony, Leonard Slatkin and Walter Susskind, conductors; Holst, "The Planets," St. Louis Symphony, Susskind, conductor; R. Strauss, "Til Eulenspiegel," "Don Juan," "Rosenkavalier Waltzes"; Salsome; Dance of the Seven Veils, Cincinnati Symphony, Thomas Schippers, conductor; Rachmaninoff, Symphonic Dances"; Vocalise," Dallas Symphony, Donald Johanos, conductor). You cue the record, and even with volume control turned up, there is no surface or groove noise from the speakers. The music emergers from a velvety silent background with astonishing impact and dynamic range.

In addition to listening, I made some sound-pressure level measurements. Then, to make certain I wasn't deluding myself, I repeated the tests with all four albums. The measurements show that for the same setting of the volume control, the dbx technique actually lowers the playback system's own noise by a few decibels. Without the dbx, my system was running a bit over the prevailing noise-level of my room. With the dbx in, the system noise dropped to (or below, for all I know) that noise level.

Even more telling was what happened in the opposite direction. Without dbx, I was averaging, for a given setting of the volume knob, some 73 dB/SPL. With dbx, this level went up to 83 dB, with peaks of 90 dB sounding completely clear and natural. So not only was the residual noise reduced, but the overall dynamic range was considerably expanded, and with no rise in distortion or other undesirable effects.

This improvement in terms of disc recordings seems more dramatic than what Dolby has done for tape recordings. What it means is that the record-cutting process no longer need be a limitation on the quality of the original master tape (it is, even for digitally-made master tapes). Short of an actual digital disc (which is at least five or more years away), the dbx type of disc is nothing less than the best I know of. Its improvement over all others is both audible and measurable. It seems to me that record companies should start using it, and that equipment manufacturers ought to include the dbx decoder as an integral part of amplifiers and receivers. Both these changes could probably be done by licensing from dbx. The added circuit in equipment probably would raise the cost somewhat, but this increase would make more sense than the added cost of many recent "cosmetic" embellishments that do nothing to improve the sound. FEED BACK

Q: On my two-set antenna splitter, it says there is a 3-dB loss to each of the sets connected. Does this apply only when both sets are turned on at the same time?

A: No. The signal loss exists as a result of the hookup whether either or both sets are tuned on. In many instances, however, the loss is not enough to seriously impair reception. If the loss proves too great, you may need to install a signal booster in the original line that feeds into the splitter. Check with your dealer.