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Dolby C improves on Dolby B in some impressive ways. Here are some test results.
  technofile
Al Fasoldt's reviews and commentaries, continuously available online since 1983

Audio cassettes with Dolby C show big advances


By Al Fasoldt
Copyright © 1986, The Syracuse Newspapers
   While the inventors of the latest digital audio components are exploring new ways of storing and reproducing sound, the old technology remains competitive. Signs that mass-produced cassette recordings are keeping up with improvements elsewhere come from a major recording company whose name cannot, at present, be revealed.
   The secrecy is not a mystery. The company has not yet committed itself to the improved techniques, and simply wants to experiment with its cassette recordings and get the reaction of industry insiders and selected critics. I was sent two of the experimental tapes for evaluation.
   They are both rock music recordings, not the best type for judging quality, but I put aside a few of my audiophile prejudices and tried to listen to them as a perceptive rock fan would. After repeated listening sessions, I came away encouraged and delighted.
   The technology being tried out has two elements. The first is the use of higher quality blank tape and cassette shells.
   Although tape itself is surprisingly cheap (less than 50 or 60 cents for the tape in a standard-quality cassette that retails for about $5), a small increase in the quality of tape stock can add up to a major added expense when hundreds of thousands or even millions of tapes are duplicated.
   The shells used in most mass-produced cassette recordings are little more than protective coverings. Most of them do not have the guidance pins and wheels common to high-quality blank tapes such as those from TDK.
   As far as I could tell, the shells of the two tapes I was sent still fell sort of the best from TDK, but they did seem better put together than previous shells from the same recording company. Internal tolerances are said to be tighter in the new shells in order to keep the tape from skewing when it passes over the playback head.
   Of greater interest were the two small logos on the spines of the cassettes. They indicated that each tape was duplicated with the latest consumer noise-reduction technique, the Dolby type C system, and that each was processed through an HX Pro circuit. These represent the second element in the quality improvements.
   Dolby C is built into nearly every cassette deck sold today. By a clever manipulation of signals during recording and playback, it is able to force tape noise far down below the level of the music.
   Only a Dolby-C tape deck can get the full benefit of C-type tapes, but HX Pro is a distortion-reducing circuit that operates during recording only. Thus any playback machine - even an inexpensive Walkman player - will show an improved sound from HX Pro recordings. (The name, in its backward phraseology, stands for Headroom Extension, Professional-type.)
   On e of the worries expressed privately by recording company executives is that tapes duplicated with Dolby-C encoding will be played back without complementary decoding. In other words, they might be played with a cassette deck's noise-reduction switch in the Dolby B" position - or listened to on a portable player without any noise reduction at all.
   The Dolby company insists that in either case the tape will not sound bad. Admittedly, engineers say, a Dolby-C tape played without any decoding in playback will seem a little strange, since soft high-frequency sounds are greatly boosted in recording. But, these engineers maintain, a Dolby-C tape played back with Dolby-B decoding will sound fine.
   To test these claims, I listened to the two tapes first without any noise reduction. They were slightly hissy, like the sound of a distant FM station. And, also like some of the distant FM stations that I can pull in were I live, they seemed lifeless and compressed while appearing too bright. Voices jumped out of an unnatural, sandpapery texture, as if someone at the studio had turned the treble control up all the way.
   Next, I switched on the standard noise reduction system, Dolby B. The tapes immediately sounded normal. They did not sound good, but most rock recordings don't sound good anyway; they had adequate "punch" but not a real sense of lifelike dynamic range.
   Finally, switching in the Dolby-C circuit of the Revox B215 cassette deck that I was using revealed subtleties in both tapes that I had missed before. Tape noise dropped from the now-you-hear-it to the now-you-don't category, and all the sounds that I could identify - at least all the acoustic sounds, ones that weren't synthesized - seemed richer and snappier. Voices, in particular, gained a clarity that made lyrics easier to understand and easier to enjoy.
   The comparison listening made it clear that tapes made with HX Pro and Dolby C can sound excellent when mass-produced. The surprise was that they could sound acceptable when played back using Dolby-B circuitry.
   This is good news for music lovers. If recording companies - especially the large corporation that made my experimental tapes - can persuade record and tape stores to stock only Dolby-C tapes instead of both Dolby-B and Dolby-C versions, consumers will find a better selection of higher quality recordings. And prices should come down if duplicate inventories are avoided.
   However, such a move may be far off, since the unknown factor is whether most large recording companies are even interested in Dolby C at all.
   Small audiophile labels have been selling Dolby-C tapes for some time, but the major firms have yet to commit themselves to the new system. Until that happens, such recordings as the two special tapes I received will be no more than tantalizing reminders of a superior technology.