stever@tektronix.UUCP (10/06/84)
-frequencies, but from what?
>From FM stereo or TV stereo or both? When is it useful to filter out
high frequencies?
steve
tektronix!stever
paul@wjvax.UUCP (Paul Summers) (10/09/84)
> PCM Recording and Playback in the SONY SL2710 Manual refers I think to > connecting up a digital tape machine? ... > Maybe someone else can explain what the "PCM" as in PCM/CAPTIONS switch > referred to on page 8 of the manual. I understand CAPTIONS, but do not > understand the association with PCM. PCM stands for Pulse Code Modulation. What it means is if you want to sink some heavy bucks into SONY's pulse code modulator, you can record and play back digitally on your vcr. The pulse code modulator converts an analog audio signal into digital information, then encodes it in such a way that it can be recorded on a vcr (PCM). Play back is just the reverse. This gives you comparable specs to a compact audio disc, but also gives you recording capability (not to mention a much longer uninterupted playback time). These things ain't cheap, and unless you are going to copy compact disks or make live recordings, it probably isn't worth the money. I don't know of anyone distributing audio recordings on this medium. > In addition, I am not clear about the manual's reference to MPX. I > understand the function of the MPX output jack, but what is the MPX > filter? It apparently filters out high-frequencies, but from what? > From FM stereo or TV stereo or both? When is it useful to filter out > high frequencies? Multiplex stereo broadcasts (FM or TV) are (or will be) identified to your receiver by an 18KHz pilot tone (at least for FM broadcasts. I haven't heard any specs for stereo TV). The presence of this carrier notifies the receiver that a stereo signal is present. The audio bandwidth of the signal stops at 15Khz. The multiplex filter takes out the carrier signal. The reason for this is that if you are making a recording of the broadcast, the presence of the tone can fool an automatic volume control, or noise reduction circuitry (Dolby and Dbx get hopelessly confused if the MPX tone is present.) -- Paul Summers Watkins Johsnon, Co. San Jose, Ca. (...ios!wjvax!paul)
rfg@hound.UUCP (R.GRANTGES) (10/09/84)
[.] The answers to the "multiplex" question that I have seen have missed an important point. The multiplex filter is provided for the reasons reported: to remove the 15 khz) pilot tone from any FM signal fed into the VCR top be recorded. The multiplex output jacks are provided to feed signal to a yet to be purchased (they hope) stereo decoder for stereo TV signals yet to be broadcast. In otherwords, they did not build in the stereo receiving capability, it's add on. Same is true for the SL2700. Dick Grantges hound!rfg
msc@qubix.UUCP (Mark Callow) (10/10/84)
> Multiplex stereo broadcasts (FM or TV) are (or will be) identified to your > receiver by an 18KHz pilot tone (at least for FM broadcasts. I haven't heard > any specs for stereo TV). The presence of this carrier notifies the > receiver that a > stereo signal is present. The audio bandwidth of the > signal stops at 15Khz. > The multiplex filter takes out the carrier signal. The reason for this is > that if you are making a recording of the broadcast, the presence of the > tone can fool an automatic volume control, or noise reduction circuitry > (Dolby and Dbx get hopelessly confused if the MPX tone is present.) > The pilot tone is 19kHz. It is far more than an indication to your receiver that it is receiving a stereo signal. It controls the PLL (phase--lock loop) used to demultiplex the two frequency multiplexed channels. (l+r and l-r). -- From the TARDIS of Mark Callow msc@qubix.UUCP, qubix!msc@decwrl.ARPA ...{decvax,ucbvax}!decwrl!qubix!msc, ...{amd,ihnp4,ittvax}!qubix!msc "Nothing shocks me. I'm an Engineer."