On the subject of end-of-side distortion of vinyl LPs:

I wonder if some of the distortion people hear is not just the
`end-of-side compression' which is a function of the of the reduced
stylus-vinyl relative speed (and hence I assume we can't `cure'), but a
combined effect of this compression and the dreaded mould release agent
(MRA). To elaborate.... 

I have had a few records recently that seemed to have developed a course
treble in the last tracks indicating I was having trouble with tracking at
high frequencies, and also a slightly muddled sound. I had been cleaning
the records with a Hunt Mark 6 brush with MRA `dissolving-fluid' and so I
assumed they were clean. Hence I put this distortion down to my stylus
wearing and/or the record wearing. However, I had got lazy, and instead of
placing the record on a flat surface and pushing the cleaning brush around
by hand (as per the instructions), I had taken to putting the LP on the
spinning platter and holding the brush still. It does appear to work fine
for new UNPLAYED records (and for `topping up' the cleaning process), but
I now realise it's not so good for LPs that are already played. 

In cleaning on the spinning platter, the brush obviously cleans in an
anticlockwise direction relative to the record.  However, I read recently
an article by Keith Hunt who stressed the importance of cleaning
CLOCKWISE. He reckoned (heavy paraphrasing) that as the stylus travelled
along the groove in an anticlockwise direction (again relatively
speaking), the leading edge of a modulation is kept relatively clean, but
MRA would gather in the `shadow' of the trailing edge of the modulation
due to the reduced stylus-vinyl contact pressure at this point, and
anticlockwise cleaning had a tough time getting this MRA out of these
nooks and crannies. 

So I resurrected this cleaning method, with the record stationery, and
pushing the brush around the record in a clockwise direction. I was
amazed; when playing what I thought was already a `clean' record, the
harshness and muddying of the sound in the last tracks had gone. I tried
this on a load of records, and the results were the same. I also tried it
on LPs that I remember I had cleaned on the spinning platter before they
had been played, and I found that they also significantly improved. So I
would conclude that initial cleaning still leaves a fair bit of MRA in the
grooves which then collects in the trailing edges of the `bumps' in the
groove. 

I would expect that for a modulation resulting from a given sound (same
amplitude and same duration etc), the `gradient' of the leading and
trailing edges of that modulation would be far greater at the end of a
side due to diminished stylus-vinyl relative velocity. I would hence
expect that MRA would find it easier to hide in these end-of-side trailing
edge shadow areas. Perhaps some ASCII art might be in order: 


     direction of stylus motion ----------->

                     _____________
                  /                 \.             Outer Track
               /                       \..         Modulation Profile
           ./                             \ ...  
     ------                                  ------

                                  
               _____           
             /       \..                           Inner Track
           ./         \.....                       Modulation Profile
         ../           \.......
     ------             --------------             ... = MRA

           
           Profiles resulting from the `same sound'
           ----------------------------------------

The additional MRA contamination in these end-of-side tracks surely must
inhibit tracking - I suspect the main reason for the subjective distortion
at end-of-side. Certainly when I make an effort to clean the LP properly
as described, I have difficulty in noticing any degradation in the music
towards the end of a side. 

You people might do all this cleaning already, but if not I urge you to
try, paying particular attention to the CLOCKWISE cleaning. It really is
quite shocking when you realise just how much better a clean record
sounds. 

For your information, the Hunt Mark 6 brush is one of these things with a
row of carbon fibres on each side, with a nylon-velvety type pad (you know
the type) in the middle. I use Goldring Magic record cleaning spray which
is applied to the leading row of carbon fibres only (this is important).
The brush is pushed around the LP with no downward force being applied
(gravity is enough). I intend to pickup an old el cheapo record player,
and convert it so it spins anticlockwise, and use the arm to hold the
brush stationery. Should prove an effective record cleaning machine, not
to say cheap. 

Cheers

Neil McBride
Unit for Space Sciences
University of Kent
Canterbury
UK




PS: (added in 1997)....  I did indeed hack an old turntable to get the
platter revolving the `wrong way' so that I could clean my records much
more easily. It worked astoundingly well in fact. With the Goldring Magic
the LPs sound really excellent.

Unfortunately, Goldring Magic was a volatile CFC (in fact it was basically
`Arclone' made by ICI) and is now a restricted substance. This has been a
bit disastrous for the record cleaning. Nothing else I have tried comes
close. A 50/50 mix of pure ethanol and water isn't too bad, but just
isn't volatile enough such that it leaves the LPs wet. OK, if you have a
vacuum cleaning system but not much good otherwise. If any one has any
ideas as to a replacement for the Magic, please let me know.