In listening to the latest offering from the dbx record-curring process it is easy to become dissatisfied with all other disc recordings, at least from the standpoints of quiet surfaces and dynamic range. You cue up one of these records, turn up the volume, and with the stylus in the portion of the groove before the actual music starts you hear utter silence. The program then starts with the music emerging in full dynamic scope that is at first startling, but soon becomes properly dramatic a musical point of view. If anthing, these latest albums are even better than the last releases.

The story this time is the wedding of digital master tapes to the dbx cutting technique. The digital tape can be recorded in full dynamic range, just about the 90-db span you would experience at a live concert in a good hall. The dbx cutting process permits capturing that range on an analogue disc by compressing the tape's dynamic range linearly in a 2-to-1 ratio.

In this way the record cutter is "fooled" into handling what it "sees" as only 40 to 50 db of dynamic range. No trouble at all in cutting that.

On playback, the dbx "decoder" expands that dynamic range by an inverse ratio so that the full range is restored. At the same time, whatever noise was generated during the cutting process is "expanded downward" -- i.e., decreased to inaudibility. FEEDBACK

Q: I hooked up my TV sound to bypass the TV set's own audio section, and fed it via shielded cable to my stereo receiver. Sometimes the volume is overwhelming, and I often hear high-frequency distortion. Any ideas on this?

A: I can only guess, but one possible cause is that your sound take-off was made to the "top" of your TV set's volume control. If so, rewire it to the "swinger" so that you can control the signal level entering your stereo system. Another possible cause is that the signal cable is plugged into the wrong jack on your receiver. Only the one marked "tuner" or "auxiliary" should be used. If both of these causes are ruled out, it may help to wire in a separate volume control for the TV sound leaving the set. A 500-ohm control should suffice. If you're in doubt as to wiring it in, consult a local audio dealer.

Q: On the strength of your review, I bought a Bic T-05 cassette deck. I am fairly pleased with it, but would like to know more about what tapes were used in your tests. I am using BASF high-bias tape. Also, the use of the Dolby (NR and MPX) does not seem adequately covered the the BIC literature.

A: In our lab tests we used TDK type AD and type SA for normal and high bias respectively, but there is no reason you cannot get equally good results with any standard branc, including BASF. The Dolby NR switch has three positions and is marked on both sides of the switch for Dolby NR and for MPX. Use the top position (Dolby NR on and MPX on) only when recording FM off the air with a tuner that fails to suppress the supersonic multiplex guidance signals used in stereo FM broadcasting. Most recent tuners and receivers do suppress that signal, which obviates the need for the "MPX on" switch position. Use the middle switch position (Dolby NR on, MPX off) for any recording in which you want to introduce noise-reduction, and for playback of any cassettes that were recorded with noise-reduction. Use the bottom switch setting (Dolby NR off, MPX off) for recording a broadcast or another tape that has been Dolbyized, but return to the center position for playing back that tape.

These rules, by the way, apply to all cassette decks that have the MPX feature tied in with the Dolby switch.