jon@boulder.UUCP (Jonathan Corbet) (02/10/85)
[]
I have heard rumors from a couple of sources now that some record
companies are adding a high frequency signal to their records that
interfere with the bias on tape decks, thus making it difficult to make
tapes of said records. Does anybody know if this is really true, and
if so, just what the technique is?
--
Jonathan Corbet
National Center for Atmospheric Research, Field Observing Facility
{seismo|hplabs}!hao!boulder!jonron@brl-tgr.ARPA (Ron Natalie <ron>) (02/11/85)
> > I have heard rumors from a couple of sources now that some record > companies are adding a high frequency signal to their records that > interfere with the bias on tape decks, thus making it difficult to make > tapes of said records. Does anybody know if this is really true, and > if so, just what the technique is? > 'Twould seem to me that any signal high enough to be inaudible and also interfere with my tape deck bias would also be severely diminished by the fact that my stereo rolls off the high end very quickly above what I find to be inaudible (which is higher than most people). Since they are obviously targeting this at cassettes, all you'd have to do is zap your equalizer to not try to record above the top level that cassettes are capable of recording. The only thing I could think of is that they are beating the bias frequency down to something audible to ruin the recording.
saf@clyde.UUCP (Steve Falco) (02/11/85)
> I have heard rumors from a couple of sources now that some record > companies are adding a high frequency signal to their records that > interfere with the bias on tape decks, thus making it difficult to make > tapes of said records. Does anybody know if this is really true, and > if so, just what the technique is? In the first place, this will cause all kinds of noise and modulation problems in a lot of equipment (not to mention blown treeters) so I doubt any company is dumb enough to try it. Also, any tape-deck that is even slightly respectable has a filter to remove the stereo pilot when recording from FM radio. The filter would presumably be able to handle a deliberate "copy protection" signal as well. Fear not! Steve Falco AT&T Bell Laboratories
herbie@watdcsu.UUCP (Herb Chong [DCS]) (02/11/85)
In article <305@boulder.UUCP> jon@boulder.UUCP (Jonathan Corbet) writes: >[] > > I have heard rumors from a couple of sources now that some record >companies are adding a high frequency signal to their records that >interfere with the bias on tape decks, thus making it difficult to make >tapes of said records. Does anybody know if this is really true, and >if so, just what the technique is? > >-- >Jonathan Corbet >National Center for Atmospheric Research, Field Observing Facility >{seismo|hplabs}!hao!boulder!jon i think that this rumor is false. most cartridges do not have enough high frequency response to deliver such a signal at a sufficient level to affect taping by overbiasing. remember that about the minimum acceptable frequency for bias is about 90kHz. if the signal was sufficiently high in level to be reasonably reproduced by the majority of cartridges, almost all would not be a able to track it. also, most cutter heads do not reproduce past about 35kHz. the CD-4 records that required response to 50kHz were all half-speed mastered to get around this problem. Herb Chong... I'm user-friendly -- I don't byte, I nybble.... UUCP: {decvax|utzoo|ihnp4|allegra|clyde}!watmath!water!watdcsu!herbie CSNET: herbie%watdcsu@waterloo.csnet ARPA: herbie%watdcsu%waterloo.csnet@csnet-relay.arpa NETNORTH, BITNET, EARN: herbie@watdcs, herbie@watdcsu
doug@terak.UUCP (Doug Pardee) (02/12/85)
> I have heard rumors from a couple of sources now that some record > companies are adding a high frequency signal to their records that > interfere with the bias on tape decks, thus making it difficult to make > tapes of said records. Does anybody know if this is really true, and > if so, just what the technique is? Well, it won't work with *my* cheap cartridge!! :-) -- Doug Pardee -- Terak Corp. -- !{hao,ihnp4,decvax}!noao!terak!doug
rcd@opus.UUCP (Dick Dunn) (02/12/85)
> > I have heard rumors from a couple of sources now that some record > > companies are adding a high frequency signal to their records that > > interfere with the bias on tape decks, thus making it difficult to make > > tapes of said records. Does anybody know if this is really true, and > > if so, just what the technique is? It's not clear whether this might refer to the actual bias for the recording or (rumors being what they are) to introducing a bias which would screw up Dolby tracking. > 'Twould seem to me that any signal high enough to be inaudible and also > interfere with my tape deck bias would also be severely diminished by > the fact that my stereo rolls off the high end very quickly above what > I find to be inaudible... Good point. Consider another related one--a record company might want to be damned careful about recording ultrasonics which can fry tweeters (when passed thru a superb cartridge and one of those idiotic DC-to-light preamp/ amp combinations). And yet another--do you want music or a new way to call your dog? I can think of lots of reasons that make the rumor unlikely. > ...all you'd have to do is zap > your equalizer to not try to record above the top level that cassettes > are capable of recording. Another good way would be to kick in the MPX filter that's present on most decks--this is a filter designed to get rid of any residual of the 19 KHz "pilot" signal in FM stereo signals. In fact, the reason you have the MPX filter is just to prevent Dolby mistracking. I'm pretty sure that these filters are lowpass (rather than notch--can anyone confirm or correct?), so this should handily get rid of any HF junk. > The only thing I could think of is that they are beating the bias > frequency down to something audible to ruin the recording. This doesn't seem likely either--bias is commonly some 105 KHz, so to beat it on down the line (oops) to audio, you've got to come in above 85 KHz. That's a tall order for most cartridges, and there are lots of other places in the system to lose a frequency that high. It wouldn't surprise me to know that record companies are working on something to make it difficult to tape LP's--i.e., finding one more way to screw up the waning fidelity of the garden-variety LP. I just wish they'd attack the problem by making decent tapes available instead. -- Dick Dunn {hao,ucbvax,allegra}!nbires!rcd (303)444-5710 x3086 ...Cerebus for dictator!
dave@rocksvax.UUCP (02/12/85)
The bias beat problem may not be a problem. I haven't looked at any
deck circuits but it seems that the cassette machines might have low pass
filter already built in that cuts off any frequencies that might
beat with the bias oscillator. Maybe cheap decks leave this out, but
it seems to me that you would this to prevent high frequency
noise components and the like from the pre-amp from intermodulating
with the bias.
Of course good pre-amps will not have much noise and this would not be
a problem anyways. If they really are doing this I think is sucks, how am
I going to play an album in the car, which is usually what I tape albums/CDs
for. Then again a CD won't have any of that nonsense encoded in it.
Another thing to do might be to mount up your favorite 'nail' -:) and play
the album once, that ought to wipe out those offending high frequencies. -:)
Dave
arpa: Sewhuk.HENR@Xerox.ARPA
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