wjm@whuxj.UUCP (MITCHELL) (06/05/84)
<munchies?> For those of you interested in a mid-priced cassette deck, Consumer Reports has an evaluation in their June 84 issue. While I don't agree (as always) to their policy of boiling the entire report down to one numerical score, I certainly agree with their recommendation for noise reduction. They believe that dbx is the most effective means of noise reduction, and recommend the use of an outboard dbx 224 if your tape deck doesn't have built-in dbx. Bill Mitchell (whuxj!wjm)
fish@ihu1h.UUCP (Bob Fishell) (06/06/84)
(oo) >I certainly agree with their recommendation for noise reduction. They believe >that dbx is the most effective means of noise reduction, and recommend the >use of an outboard dbx 224 if your tape deck doesn't have built-in dbx. >Bill Mitchell (whuxj!wjm) I'll go along with this, too, but with a caveat. dbx noise reduction works by preemphasizing the high frequencies and compressing the program dynamics on the encoding pass, and by reversing both processes on the decoding pass. The result is dead silence where no recorded signal is present, something Dolby does not quite achieve. However, the encoding process tends to tax the high frequency capacities of the tape and deck. This is no problem for open reel decks or for certain high-quality cassette decks, which have a frequency response well in excess of the limits of human hearing. However, use of dbx without a deck and tape capable of extended high-frequency response will result in an unpleasant "pumping" sound. I use a dbx 224 with my open-reel deck, but I've found that Dolby C is perfectly adequate for cassette recording. Dolby does not give you the headroom that dbx does for, say, recording from compact discs, but is probably better suited to the cassette medium. Besides, dbx-encoded tapes sound awfully funny when played back without decoding. Some auto tape players are now available with dbx, but most only have Dolby B, if anything at all. Dolby C is compatible for playback on Dolby B (it isn't linear, but it doesn't sound too bad), but dbx isn't. In short, dbx is better, but not as flexible. -- Bob Fishell ihnp4!ihu1g!fish
czp@houxa.UUCP (C.PODARAS) (06/06/84)
i believe that dbx markets a small playback adaptor meant for use with walkman-type tape players, and also one for automotive use. neither are very expensive, and i remember seeing them advertised by j&r music world (new york city) in the ads which they run in audio magazine. chuck p houxa!czp
fish@ihu1g.UUCP (Bob Fishell) (06/11/84)
(oo) >What? I think I'll pick a few nits on this reply since I'm feeling irritable. >dbx does NOT work by preemphasizing the High frequencies of the compressed >signal, to my recollection, but does play tricks with the signal presented >to the RMS detector. High frequency response of the tape deck shouldn't have >much to do with the reconstruction quality, since the RMS detector only looks >at signals below 10kHz. >(...,) >the wandering squash, > >-- > Shaun Simpkins The following is a quote from the instruction manual issued with the dbx Model 1BX dynamic range expander (page 14): "[dbx] noise reduction is accomplished by a 'compander,' a circuit which compresses the program before recording, and expands the program during playback. In addition, dbx tape noise reduction systems apply pre-emphasis of high frequencies before recording, and de-emphasis upon playback to further reduce high frequency noise (hiss) and tape modulation noise" Now, my sources are pretty succinct. Where did you get your information? -- Bob Fishell ihnp4!ihu1g!fish
shauns@vice.UUCP (06/13/84)
Simple. My recall wasn't perfect. The preemphasis mystically moved from the
signal path to the control path as the info sat in my brain. Still, the way
out of this problem is to move the postcompression signal level down. You guys
with onboard dbx can't do this readily; sorry 'bout that.
The corrected wandering squash,
--
Shaun Simpkins
uucp: {ucbvax,decvax,chico,pur-ee,cbosg,ihnss}!teklabs!tekcad!vice!shauns
CSnet: shauns@tek
ARPAnet:shauns.tek@rand-relaytynor@uiucuxc.UUCP (06/15/84)
#R:whuxj:-26800:uiucuxc:18500032:000:481 uiucuxc!tynor Jun 14 22:11:00 1984 >> I was just told that the units you mention have been pulled from production >> and no plans exist to market them in the future. I'm depressed. Don't get too depressed. Concord still makes an auto dbx decoder. (If they have decided to pull the plug on their unit let me know. I'll rush out and buy one before they're all gone. Else *I'd* be depressed too.) Steve Tynor ihnp4!uiucdcs!uiucuxc!tynor University of Illinois Champaign-Urbana