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Re: It's in the grooves

Thanks for your reply. I think I know what you are getting at.

*** As I'm writing this I have before me Telarc's 1812 Overture on vinyl. By looking at the grooves (with the naked eye) you can see where the canons hit. With even a magnifying glass of even weak strength can see where the canons hit to the nano second, and you will say to yourself, wow! It is no wonder that tone arms have difficulty staying in the grooves at that point. The grooves have shear rises and drops. The grooves are very wide, almost like the unused space between the end of the music and the label. ***

The widening of the groove spacing is a common technique to allow loud passages to track better. But it does not mean that a well designed and properly setup turntable is not able to track loud passages in narrow grooves.

As I've said before, I have transferred quite a few LPs to digital (probably a quarter of my collection). I can tell you there is very little correlation between the actual dynamics present on the LP and how wide the groove spacing (apparently) is. I have seen LPs with very narrow groove spacing that has dynamics far in excess of LPs with wide groove spacing.

I think you are probably underestimating the ability for a well designed stylus to track very sudden and loud transients. If you think about it, that's what a scratch (which creates a loud "pop") looks like to a needle. Most good LP decks should have no problems even tracking very deep scratches (of course, whether the amp and/or speaker can reproduce the resultant spike is a different matter - I tend to agree with you that most systems struggle with very large and sudden transients - I have measured "pops" from scratches in excess of +10dBFS - which is why I always allow 12dB of headroom when transferring from LP).

I generally find that even deep scratches produce very clean transients, in fact far cleaner than I would have thought possible given issues with arm and/or platter resonance, stylus tracking etc. On most of my transfers, scratches/pops come out as an almost perfect square impulse lasting 1-5 samples, which means a "pop" generally lasts for less than a millisecond, with no signs of ringing or other artefacts associated with mistracking. They are so clean I can easily digitally edit them out (and I do, for the really intrusive ones).

So, if a stylus can track pops so well, one can infer it should be able to handle "normal" music (yes, even the cannons in 1812) with no problems, even if the groove spacing is narrow.

As for SACD, the amount of compression you can achieve depends on the material. I wouldn't be surprised if a very dynamic recording of an orchestra compresses less than a quiet recording. Hence issues in terms of the maximum amount of playing time per disc - it varies (slightly). In the extreme case, pure noise does not compress at all, hence a recording of pure noise would take up twice as much space as a "normal" piece of music (DST, the lossless compression scheme for SACD, is designed for a target compression ratio of about 2:1).

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