don@oakhill.UUCP (Don Weiss) (12/29/84)
>> The best way I have found to dub CDs is actually onto open reel, 1/4 inch, >> half-track tape at 15 ips with DBX type 1. > ... >> Said method actually provides better noise performance than dubbing to >> digital VCR tape, using either a Technics SV-100 (EIAJ 14-bit) or Sony >> PCM-701ES (using 16-bit format). ... >> in fact if not for the cost, I'd probably do all my dubbing onto analog in >> the manner mentioned above. >Hmmm... I don't hear any noise when I dup CD's with my Nak DMP-100 (16-bit). >Maybe I am not listening well enough or the tweaking that Nak requires is worth >it (the Nak is a Sony that meets Nak's tolerance specs). Any idea where the >noise comes from? Were those CD's digitally mastered? > --Cliff [Matthews] Let me give some detail on the experiments that led to the conclusion about the relative noise performance of the two methods described above. Frst, I digitally dubbed the new digitally-mastered Columbia recording by pianist Cecile Licad of Rachmaninov's second Piano Concerto, with Claudio Abbado conducting. I used a Technics SLP-7 CD player, a Technics SV-100 PCM box, and a Quasar W5310 VCR (I guess that last is irrelevant!). I decided to critically A-B the digital dub with the original CD. They were quite indistinguishable exept in the intervals of digital zero between cuts and also in some of the very quietest recorded passages...for instance, at the end of the slow movement, with some very pianissimo piano keystrokes, the digital dub displayed audibly greater background hiss than the straight CD playback. Being startled at this phenomenon, I repeated it with a very careful adjustment of recording level (to the absolute maximum possible on crescendos) and balancing of playback levels between the tape and CD; the result was the same. I then decided to fire up my trusty Technics RS1500US open reel tape machine with its outboard dbx model 150 (type I) noise reducer. I ran the 1/4" half-track machine at 15 ips just for grins. The result of the same "live-vs. memorex" test was that there was absolutely NO noise buildup audible under any signal condition. Later, I borrowed a friend's Sony PCM-701ES PCM box and reran the experiment with it, in 14 and 16 bit modes. The result was essentially the same as with my Technics box. The source of the noise was suggested by the experiment of turning the record volume on the PCM box all the way down, beginning a (blank) recording with record muted, and then recording some more with record unmuted. There were substantial increases in the playback noise level between (a) playback muted, (b) playback unmuted and record muted, and (c) playback and record unmuted with record level set at zero. It would seem, therefore, that the analog circuits preceding the A->D conversion are in need of improvement; I wouldn't be surprised if your (Sony --->)Nakamichi tweaks include this area. I ran one final experiment: I set up a 1 KHz oscillator with a wide range step attenuator on its output so that it produced maximum record level (as verified on a video monitor). I then ran a test recording, starting with the maximum level and reducing it in 10 dB steps to -80 dB of its original value. On playback, the tone seemed to sink below the broadband noise by the -80 dB step. Thus, I'm not convinced that the PCM boxes are delivering all the S/N (i.e. 86 dB) that they're supposed to. I'll have to find a really sensitive AC voltmeter to find out. -----Vive l'numerique! Don Weiss
cliff@unmvax.UUCP (01/07/85)
> >> The best way I have found to dub CDs is actually onto open reel, 1/4 inch, > >> half-track tape at 15 ips with DBX type 1. > > ... > >> Said method actually provides better noise performance than dubbing to > >> digital VCR tape, using either a Technics SV-100 (EIAJ 14-bit) or Sony > >> PCM-701ES (using 16-bit format). > ... > >> in fact if not for the cost, I'd probably do all my dubbing onto analog in > >> the manner mentioned above. > > >Hmmm... I don't hear any noise when I dup CD's with my Nak DMP-100 (16-bit). > >Maybe I am not listening well enough or the tweaking that Nak requires is worth > >it (the Nak is a Sony that meets Nak's tolerance specs). Any idea where the > >noise comes from? Were those CD's digitally mastered? > > --Cliff [Matthews] > > > Let me give some detail on the experiments that led to the conclusion about > the relative noise performance of the two methods described above. informative article followed Thank you very much for the article. When I get some free time I will try to duplicate your tests on my PCM processor and my girlfriend's CD (NAD 5200), of course I will post my results. Do you know whether the space between tracks on CD's is just 0's or is there circuitry that totally mutes the analog output for a period of time? I am not sure and I have been to lazy to research it... --Cliff [Matthews] {purdue, cmcl2, ihnp4}!lanl!unmvax!cliff {csu-cs, pur-ee, convex, gatech, ucbvax}!unmvax!cliff 4744 Trumbull S.E. - Albuquerque NM 87108 - (505) 265-9143