[net.audio] Print-thru: Magnetic or Mechanical

jc@cvl.UUCP (John Canning) (11/07/85)

Several recent net.audio postings have talked about print-thru problems
on vinyl disks.  I've always thought that 'pre-echo' was due to the music
etched into the next groove of the record affecting the groove in which
the needle is located.  It seems unlikely to me that the very weak
permanent magnetic fields emanating from a layer of tape could affect
the adjoining tape layers on the reel.

  If it is a magnetic phenomenon, then the way in which the reel is
wound should have litte effect on the print thru because the adjoining
layers of tape have just reversed position.  The magnetic particles
are on only one side of the tape, but the distances between layers
remain the same.  Thus, depending on winding direction one would get
either pre-echo or post-echo.  Post-echo may not be as easy to detect
because the sound usually has a longer decay time than rise time and the
ear can't adjust to hear faint sounds after a loud passage.
The pre-echo time delay constant would be a function of the position on
the tape of the music since the reel diameter (and circumference) vary
with position (and change order when wound backwards).

  If it is a mechanical phenomenon, then it should be stronger in one
channel (the channel etched on the side adjoining the next groove) than
the other.  The record should also be in the same orientation at the
onset of the pre-echo and at the onset of the corresponding music.
Since I don't have any records with noticeable print-thru, I'd be interested
to hear if other people's print-thru satifies/doesn't satisfy these
conditions.

                          - John Canning (jc@cvl.umd.edu.arpa)

gvcormack@watmum.UUCP (Gordon V. Cormack) (11/08/85)

> Several recent net.audio postings have talked about print-thru problems
> on vinyl disks.  I've always thought that 'pre-echo' was due to the music
> etched into the next groove of the record affecting the groove in which
> the needle is located.  It seems unlikely to me that the very weak
> permanent magnetic fields emanating from a layer of tape could affect
> the adjoining tape layers on the reel.

I get print-through when I record from CD onto cassette.  In this
case, the print-through is DEFINITELY magnetic.  Also, on commercially
recorded tapes, you will hear print-through.  The first really bad
case I remember hearing was Led Zeppelin II  (Whole Lotta Love).
Both the record and tape of this album have print-through.  Does 
anyone out there have the CD version?

gtward@wateng.UUCP (Greg Ward) (11/08/85)

>   If it is a mechanical phenomenon, then it should be stronger in one
> channel (the channel etched on the side adjoining the next groove) than
> the other.  The record should also be in the same orientation at the
> onset of the pre-echo and at the onset of the corresponding music.
> Since I don't have any records with noticeable print-thru, I'd be interested
> to hear if other people's print-thru satifies/doesn't satisfy these
> conditions.
> 
>                           - John Canning (jc@cvl.umd.edu.arpa)

Your argument for why mechanical print through would be stronger on one
channel then the other is incorrect. You seem to be suggesting that each
channel is recorded on a different side of the groove. In fact, how the
two channels are multiplexed in the groove is that one channel is
recorded in the side to side variations of the groove, and the other is
recorded in the up and down variations.

                            - Greg Ward

gvcormack@watmum.UUCP (Gordon V. Cormack) (11/09/85)

> >   If it is a mechanical phenomenon, then it should be stronger in one
> > channel (the channel etched on the side adjoining the next groove) than
> > the other.  The record should also be in the same orientation at the
> > onset of the pre-echo and at the onset of the corresponding music.
> > Since I don't have any records with noticeable print-thru, I'd be interested
> > to hear if other people's print-thru satifies/doesn't satisfy these
> > conditions.
> > 
> >                           - John Canning (jc@cvl.umd.edu.arpa)
> 
> Your argument for why mechanical print through would be stronger on one
> channel then the other is incorrect. You seem to be suggesting that each
> channel is recorded on a different side of the groove. In fact, how the
> two channels are multiplexed in the groove is that one channel is
> recorded in the side to side variations of the groove, and the other is
> recorded in the up and down variations.
> 
>                             - Greg Ward

Sorry.  This is wrong, too.  The two channels are recorded in orthogonal
directions, but one is angled 45 degrees from vertical in one direction
and the other is angled 45 degrees in the other direction.  The phase
is applied so that the horizontal components of the two signals are
in phase and the vertical components are 180 degrees out of phase.
If you insist, this can also be thought of as recording L+R 
horizontally and L-R vertically.

rdp@teddy.UUCP (11/11/85)

In article <2860@wateng.UUCP> gtward@wateng.UUCP (Greg Ward) writes:
>>   If it is a mechanical phenomenon, then it should be stronger in one
>> channel (the channel etched on the side adjoining the next groove) than
>> the other.  The record should also be in the same orientation at the
>> onset of the pre-echo and at the onset of the corresponding music.
>> Since I don't have any records with noticeable print-thru, I'd be interested
>> to hear if other people's print-thru satifies/doesn't satisfy these
>> conditions.
>> 
>>                           - John Canning (jc@cvl.umd.edu.arpa)
>
>Your argument for why mechanical print through would be stronger on one
>channel then the other is incorrect. You seem to be suggesting that each
>channel is recorded on a different side of the groove. In fact, how the
>two channels are multiplexed in the groove is that one channel is
>recorded in the side to side variations of the groove, and the other is
>recorded in the up and down variations.
>
>                            - Greg Ward

Not entirely correct. In fact, the vertical modulation constitutes the
L-R signal, while the horizontal modulation constitutes L+R. When we
get all done figuring out how this mish-mash works, then we find that
indeed, one wall holds the right channel information, and the other
wall the left channel. The two channels are "out of phase" with one another
so that the rumble components (thought to be primarily vertical motions)
are playeed back out-of-phase.

For all intents and purposes, each wall holds one channel worth of information.

brown@nicmad.UUCP (11/14/85)

In article <2860@wateng.UUCP> gtward@wateng.UUCP (Greg Ward) writes:
>Your argument for why mechanical print through would be stronger on one
>channel then the other is incorrect. You seem to be suggesting that each
>channel is recorded on a different side of the groove. In fact, how the
>two channels are multiplexed in the groove is that one channel is
>recorded in the side to side variations of the groove, and the other is
>recorded in the up and down variations.

Sorry, but the gentleman you are referring to was correct.  On record,
each wall DOES pertain to a certain channel.

Remember, stereo and mono records are compatable.  Mono records have side-
to-side movement.  Stereo is just like that, except:

	1. When, say the left channel, is modulated and the right channel
	   isn't, the grove will not move horizontally left or right, but
	   at a 45 degree angle.  So the plain of movement is shifted at
	   a 45 degree angle.
	2. When both the left and right are modulated, in an in phase signal,
	   as the left wall is moving say, to the right and up, the left
	   channel will be moving right and down.  The net effect is that
	   the groove will move left and right on the horizontal plain,
	   making the stereo cut compatable with the mono cut.

The way you describe it, a stereo signal would have one channel not heard
on a mono turntable, because a mono cartridge only knows left and right
movement.  Yes, a single channel modulated grove moves left and right
and up and down.  The mono cartridge will pick up the signal at a lesser
volume because it will only get the left and right movement.  The up and
down energy will be lost.

What about out-of-phase signals.  Yes, they will not be heard on a mono
system, but will give the stereo listener a wierd sound effect.  The same
effect that can be heard if your mono tv signal is fed to one speaker
wired in phase and wired out-of-phase to the other stereo speaker.

To verify what I am saying, visit your local library and read about it.

Oh yes, groove modulation interference does exist.  You will get pre-echo.
I have some records that have it, and it matches the distance of one
rotation.
-- 

Mr. Video   {seismo!uwvax|decvax|ihnp4}!nicmad!brown

gtward@wateng.UUCP (Greg Ward) (11/20/85)

> In article <2860@wateng.UUCP> gtward@wateng.UUCP (Greg Ward) writes:
> >Your argument for why mechanical print through would be stronger on one
> >channel then the other is incorrect. You seem to be suggesting that each
> >channel is recorded on a different side of the groove. In fact, how the
> >two channels are multiplexed in the groove is that one channel is
> >recorded in the side to side variations of the groove, and the other is
> >recorded in the up and down variations.
> 
> Sorry, but the gentleman you are referring to was correct.  On record,
> each wall DOES pertain to a certain channel.
> 
> Mr. Video   {seismo!uwvax|decvax|ihnp4}!nicmad!brown

I have taken a lot of flack over this posting and I am prepared to
accept that my version is wrong, as the version described by others
makes more sense.

However I would like to defend myself by saying that I did not make up
my version of how the two channels are recorded in the groove, I read
it somewhere. This was a number of years ago, and I cannot remember where
I read it, so I haven't been able to look it up.

Please excuse my erroneous posting,

                         Greg Ward

rfg@hound.UUCP (R.GRANTGES) (11/21/85)

[]
Don't feel too bad. I recall that the system you described was proposed by
someone - probably edison, but the Western Electric "45-45" system is what
caught on.

-- 

"It's the thought, if any, that counts!"  Dick Grantges  hound!rfg

root@sysd.UUCP (Admin) (11/26/85)

> > Sorry, but the gentleman you are referring to was correct.  On record,
> > each wall DOES pertain to a certain channel.
> > Mr. Video   {seismo!uwvax|decvax|ihnp4}!nicmad!brown
> I have taken a lot of flack over this posting and I am prepared to
> accept that my version is wrong, as the version described by others
> makes more sense.
> 
> However I would like to defend myself by saying that I did not make up
> my version of how the two channels are recorded in the groove, I read
> it somewhere. This was a number of years ago, and I cannot remember where
> I read it, so I haven't been able to look it up.
> 
>                          Greg Ward

I believe you are thinking of the old quadrophonic SQ disks which had
light technical summaries printed on the inner sleeve of the record.
As I recall (also possibly erroneously) they described the grooves
as being "back and forth" and "up and down" (my description, not theirs).
	
						Paul Heffner
					
					{ihnp4,akgua}!bsdpkh!heffner

bprice@bmcg.UUCP (Bill Price) (11/27/85)

gtward@wateng.UUCP (Greg Ward) stands himself corrected, but...:
>> >                                                       In fact, how the
>> >two channels are multiplexed in the groove is that one channel is
>> >recorded in the side to side variations of the groove, and the other is
>> >recorded in the up and down variations.
>> 
>> Sorry, but the gentleman you are referring to was correct.  On record,
>> each wall DOES pertain to a certain channel.
>> Mr. Video   {seismo!uwvax|decvax|ihnp4}!nicmad!brown
>However I would like to defend myself by saying that I did not make up
>my version of how the two channels are recorded in the groove, I read
>it somewhere. This was a number of years ago, and I cannot remember where
>I read it, so I haven't been able to look it up.
>                         Greg Ward

Greg, it's quite likely that you did read it somewhere, long ago.  In the
very early days of stereo, both techniques were used: the
horizontal/vertical modulation was done first (i think), but it wasn't
compatible with the prior art--monophonic.  Then, someone came up with
"Compatible Stereo", wherein the horizontal modulation was L+R (=mono), and
the vertical was L-R.  Doing the arithmetic, you'll discover that this
"Compatible Stereo" scheme is exactly equivalent to (what was then called)
"45/45 [degree]" modulation, or diagonal encoding.

I don't have any records (any more) of the H/V encoding, but some of my
mid-50 oldies are labelled "COMPATIBLE STEREO".

Ain't it funny, how the L+R/L-R mono-compatibility trick gets around?
LP's, FM, AM, TV, ...

--Bill Price
-- 
--Bill Price  uucp:  {Most Anybody}!sdcsvax!bmcg!bprice
              arpa:? sdcsvax!bmcg!bprice@nosc