scott@opus.UUCP (Scott Wiesner) (01/30/85)
I've noticed that placing my Sanyo "walkman" next to my terminal
seems to cut out the Dolby. I've played with various tone settings
and Dolby in/out variants, and as from what I can judge, the terminal
(a Zenith Z19) simply eliminates the Dolby.
Any guesses as to what's going on, and whether it's affecting my tapes?
--
Scott Wiesner
{allegra, ucbvax, cornell}!nbires!scottnewton2@ucbtopaz.CC.Berkeley.ARPA (02/03/85)
I guess you're saying the Dolby (tm) noise reduction effect goes away when the Walkman is near the terminal. Most likely the horizontal scanning waveform is penetrating the audio path and paralyzing the sliding-band filter that is the core of the Dolby B (and C) NR system. The NR thinks there's substantial high-frequency energy coming off the tape, and responds by opening up its bandpass fully, which is the "correct" behavior- if the signal really *had* been recorded on the tape, the recording NR processor would likewise have slid upward to make way for the high-level 15 kHz "signal". Well designed Dolby circuits must have an effective low-pass filter at the *encoder* input to prevent signals too high in frequency for the tape to capture from triggering the encoder, and must *also* have an effective low-pass filter at the input to the playback processor to keep out spurious high frequencies which are *not* on tape. Most common source of these problem signals is tape recorder bias (on three-head so-called "double-Dolby" machines that try to reproduce decoded Dolby recordings while they're being made) and 19 kHz FM stereo pilot tone leakage. Dolby C is *very* much more sensitive to such leakage than is Dolby B. Incidentally, bias leakage can be a problem in the *record* processor if it couples into the Dolby circuit by somehow circumventing the otherwise adequate low-pass described above-- say capacitively. That's my guess for what's occuring in your situation, albeit in playback mode. Symptom would be: tape noise rises as much as 8 dB (Dolby B; 15 dB or more for Dolby C), while whatever low level highs are present are emphasized (Dolby C effect would extend down to mid-freqs).
herbie@watdcsu.UUCP (Herb Chong [DCS]) (02/04/85)
In article <1063@opus.UUCP> scott@opus.UUCP (Scott Wiesner) writes: >I've noticed that placing my Sanyo "walkman" next to my terminal >seems to cut out the Dolby. I've played with various tone settings >and Dolby in/out variants, and as from what I can judge, the terminal >(a Zenith Z19) simply eliminates the Dolby. > >Any guesses as to what's going on, and whether it's affecting my tapes? > >-- > >Scott Wiesner >{allegra, ucbvax, cornell}!nbires!scott it is possible, though i'm not sure how likely, that you're getting RF noise from the terminal inducing a signal in the circuitry just high enough to be beyond the frequency response of your headphones but not so high as to be outside the range of the Dolby circuitry. it would think that there is high frequency information from the tape and since it seems to be relatively constant, would more or less lock the Dolby circuit at one expansion/equalization position. i think that this is highly unlikely, but possible. you don't mention what you mean by `eliminate'. do the highs seem muted compared to away from the terminal? 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
gm@trsvax.UUCP (02/08/85)
Along the same lines, I have noticed that whenever I use my cordless
phone (a Panasonic) when I am watching something in Beta Hi-Fi, I hear
a loud rumbling noise from the Sony. The carrier for the cordless phone
must interfere with the playback of the Beta Hi-Fi signal. (It doesn't
happen on record).
George Moore Tandy System Software
uucp: {laidbak, sco, microsoft, sneaky, allegra!convex!ctvax}!trsvax!gm
arpa: cu-arpa.trsvax!gm@Cornell.ARPAperry@hp-dcde.UUCP (perry) (02/12/85)
The electromagnetic interference (EMI) coming from your terminal is probably
a harmonic of some resonant frequency in you tape deck. It looks like you got
quite a deal: a tape deck that's also a radio receiver :-). The EMI "soup"
is mainly caused by the video sweep circuit and to a lesser degree, the
terminal's internal clock circuits.
Over time, EMI causes the magnetic domains on tape (and floppies) to decay,
causing data loss. I store all of my tapes inside my metal desk, as far away
from the terminal as possible.
Perry Scott, HP-FSD
...{allegra|ihnp4|decvax|ucbvax}!hplabs!hpfcla!perry-s