Re: [ARSCLIST] Can 78s sound better than LPs?

[George Brock-Nannestad <pattac@xxxxxxxx>]

From: Patent Tactics, George Brock-Nannestad

Dear all,

this thread is fascinating, because so much is calculable by quite simple 
relations, now forgotten, because analog discs are no more in focus. This 
opens the field for opinions.

David Brenneman wrote:

  Another problem with a "modern" 78 would be that
> due to the larger groove, the "pinch effect" sets in 
> at a larger diameter than with a smaller groove.  An ideal
> 78 would be a 12" record with only about three minutes
> of contents.
> 

----- I have trouble understanding why a "modern" 78 should be any different 
from an ancient 78 in this respect.

----- I disagree: an ideal 78 within the normal 78rpm technology would be a 
16 inch record with only 1.3 turns on the outside diameter. It will only give 
a second of sound, but what a glorious second!!

The fact about pinch effect is that it depends on the radius of curvature of 
the stylus compared to the curvature at maximum excursion of the groove and 
the steepness of its zero crossing -- if it is line contact, then the pinch 
effect is much reduced. Also, the vertical tracking angle has to be correct 
in that case, or you will get the equivalent of azimuth distortion. Also, the 
line between the "lines" creating the line contact must go through the centre 
of the record, if the original cutting stylus had a face that did that. Not 
all of them do, particularly home recordings. However, all of the problems 
are already much reduced by the fact that the recording is likely to be 
constant velocity, which means that the steepness at the zero crossing will 
be the same for all frequencies at maximum output. Also, the radius of 
curvature at the maximum excursion will be reduced proportionally to the 
frequency.

----- good reading involving some maths will be found in the Disc Recording 
anthologies from the AES. They are well worth the money and I expect them to 
be an eye-opener to people having entered the field by digital means only. My 
copies are close to loose-leaf by now.

Kind regards,


George