fritzz@sdccsu3.UUCP (fritzz the Zebra) (08/23/84)
I'm sure you have noticed that when you play a record, occasionally you can hear the beginning of a song very faintly (maybe 25 to 30 dB quieter than normal) around 1 second before it starts. It is best heard when the song has a loud intro, and is usually most noticible on the first track of an album. I have come up with a few possible explanations, but none of them are very satisfactory. Could someone enlighten me as to why it happens, if anything can be done about it, and if there can, why there isn't. Thanks in advance, -- ihnp4--\ fritzz the Zebra decvax--\ akgua----\ "What else do you do for fun?" dcdwest---\ "I go to funerals." kgbvax-----\ ucbvax-------- sdcsvax -- sdcc3 -- fritzz
rfg@hound.UUCP (R.GRANTGES) (08/25/84)
[.] You are hearing "pre-echo". There is also "post-echo", but it is usually masked by or heard as reverberation. There are two possible sources: Recording at too high a level on the master disc, or (much less likely) "print-through" on the master tape. When the master disc is being cut by a stylus, if the stylus moves too vigorously, it will push vinyl material over into the region of the next groove. Instead of thinking of the master disk as rigid, think of it as warm fudge when the cutting stylus comes along. If the grooves are not far enough for the cutting volume,some of the modulation of one groove will merge with that of the next. Remedy: space grooves farther apart or reduce cutter excursion. Usually caused by sloppiness in the disc mastering process. When recording tape is wound on a reel (as it must be) the layers of magnetic material are seperated only by the tape backing material and the magnetic field of one layer will interact with the layers on each side. Some of this interaction is permanent and is called "print- through." How much of it occurs depends on lots of factors such as heat, humidity, other magnetic fields, tape tension, materials used for tape and backing and their thickness. Commercially this is not usually bothersome because quality tapes are handled and stored properly and recordings at 15 or 30 inches per second cause adjacent layers of tape to have sound so closely spaced that it would not be perceived as echo but rather as muddiness or distortion. With amateur recordings made at slow tape speeds (especially cassettes at 1 7/8 ips) this can be more of a problem. Depending on how the tape is wound, the print-thru will appear as pre-echo or post echo. Remedy: use good materials, proper tape handling and storage techniques. Dick Grantges hound!rfg
dmmartindale@watcgl.UUCP (Dave Martindale) (08/25/84)
This is always due to some tranfer of signal from the part of the physical media (tape or disk) where it is supposed to be to a part where it isn't. It can appear either before or after its correct place in time. If you are playing a record, note the rotational position of the disk at the point you hear the faint sound, and then when you hear it where it is supposed to occur. If the pre-echo (neat name eh?) occurs exactly one revolution before the real sound, then the problem is due to the signal in one groove distorting the groove walls of the preceding groove. If the offset in time isn't one disc revolution, then the effect is most likely due to print-through on the magnetic tape used at some point in the recording process. The offset in time in this case is one revolution of the reel of tape.
karn@mouton.UUCP (08/25/84)
This phenomenon is called "print through", and can happen with either tapes or LPs (but not CDs). The delay you hear between the "pre-echo" signal and the actual beginning corresponds to one revolution of the tape or disk. With tapes, the magnetic signal actually "prints through" one layer of the tape backing, transferring its magnetism to the adjacent layers. You hear only the first printed-through layer because there is silence otherwise before the music starts. With LPs, it is possible for the impressions of one groove to "bleed over" into adjacent grooves, depending on the groove spacing, audio level, vinyl, etc. Yet another reason to go digital! Phil
dmmartindale@watcgl.UUCP (Dave Martindale) (08/25/84)
A question: when audio tapes print-through, in which direction do they do it? In other words, with tape wrapped on a reel, does print-through generally occur between one layer of tape and the layer next to its oxide, or the layer next to its backing? (I phrase this in terms of layer next to a given layer's oxide/backing, rather than the layer inside/outside of it on the spool, since open-reel and cassette tapes are wound in opposite manners.)
mcrk@pyuxo.UUCP (C Koster) (08/26/84)
[THIS IS WHERE THE BASS GOES IN MY STEREO...] I once heard a story that had to do with the fact that some records have such thin walls in the groove that some sound would come through this is especially true when the record company is trying to fit a lot of music on an LP. I don't know if this is true or not, but it seems to make sense. Anybody out there that can confirm this?? Chris Koster pyuxo!mcrk soon to be rruxo!mcrk
adm@cbneb.UUCP (08/27/84)
#R:hound:-59600:cbneb:8300001:000:521
cbneb!rap Aug 27 10:08:00 1984
[ Only the shadow knows ... ]
The pre-echo problem is not limited to records and pre-recorded tapes.
I have a CD (I don't remember the title offhand) that has a fairly
strong pre-echo.
I guess this must have happened on the master and they didn't bother
to erase it (?zero it?). This seemed strange to me as it shouldn't
take much effort on a digital master to delete an unwanted signal
before mass producing it.
Rus Putzke
ihnp4!cbneb!rapdhc@exodus.UUCP (David H. Copp) (08/27/84)
Come now--consider a 10 1/2" reel--at the start of the reel there is about 10" of tape on it, so the circumferance is over 30". At 30 ips the printthrough echo delay is about one second, not "sound so closely spaced that it would not be perceived as echo but rather as muddiness or distortion." -- David H. Copp
rfg@hound.UUCP (R.GRANTGES) (08/28/84)
[!!] Come now yourself. What professional records at the extreme periphery of a 10 1/2 inch reel? Well, perhaps you are right, I,m not really sure what music delayed, say half a second and played backwards (or forwards depending on wind) at very low level and added to the main sound dounds like, but I'll bet it sounds more like mud and distortion most of the time. hound!rfg
rfg@hound.UUCP (R.GRANTGES) (08/28/84)
[!] In the case of "pre-echo" on a CD, you have to be talking about a CD made from an analog master. If the master were digital, the print through would have been ignored by the digital process. This is <the> <great> advantage of the digital process. Signals are recorded as binary pulses. A noise pulse has to be very large -half the size of the true pulse- before it makes any difference. This is why digital media (e.g. CD or tape) are so noise free. Of course if the "noise" gets comparable with the signal in amplitude, then things go to hell. Dick Grantges hound!rfg
brent@itm.UUCP (08/29/84)
X
About audio tape print-through. It prints through both before
and after. Usually the pre-print is worse than the post-print because
the flux is greater on the front of the oxide than on the back. It
is for this reason that archivally stored mag tapes are usually stored
"tails out"; i.e. in need of rewinding. This puts the stronger print-
through image after the sound, where is is usually more masked by
recorded ambient sound.
--
Brent Laminack (akgua!itm!brent)