Half-Speed Masters - are they worth double dipping?

First, and foremost - EVERYTHING matters.

By reducing the rotational speed of the disc by 2x, you double the amount of time that the cutterhead has to remove the material.  Consequently, there is an inherent increase in cutting accuracy.  When a stylus traces the same groove, it is more often exactly where it should be to reproduce the given frequency/sound - again, more accurate. 

This principle applies to the entire recorded spectrum - highs, mids, and lows.  In the attached article (below), an Abbey Road recording engineer states that cutting at half-speed is 'mind-numbingly dull ', but the process results in a much better sounding LP. (> @bdp24 - perhaps Bernie Grundman has concluded the boredom is not worth the time it takes for the improvement in SQ ;-).

That being said, if a crappy recording (say, compressed, dull microphone, cheap wires) is re-cut at half-speed, you may be disappointed in the result.  Remember, EVERYTHING matters. I have both fantastic -sounding and crappy-sounding half-speed LPs.

Yes, there are many other techniques to improve LP SQ, including direct-to-disc, 45 rpm, better quality vinyl, etc. and each can be independently employed.  In theory, you could have a half-speed mastered LP, pressed on uber-vinyl, that plays at 45-rpm.  

Regarding the digital vs. analogue issue, I find the transducer plays a prominent role in the SQ. 

For example: I have the same recording in both formats - simultaneously recorded on Analogue tape and Digital tape. I find a very good TT cartridge (my Hanna ML) can transform the soundwave-medium (mechanical to electronic) better than an average CD player (my OPPO, digital to electronic).  Consequently, the LP sounds better than the CD every time I compare the two. (of course, I am also hearing differences in tape-heads, etc.)

As an aside, my main system has a pretty good CD player as well (Ayre), and the SQ is closer to that of the LP.

Now the aforementioned link (begin reading at "What exactly is half-speed mastering?" 

All You Need To Know about Half Speed Mastering | uDiscover (udiscovermusic.com)

Best,

I've added a few of these over the years; I found them in the used bin at Amoeba or the local record store. The 1/2 speed versions were a duplicate to standard pressings I already had.  After a good inspection and cleaning the results are mostly mixed. Steely Dan Aja was worth the $45 used; very clean and vibrant compared to standard recording.  Doobie Bros Captain and Me also very clean, but no real sonic difference from the standard issue. Seals and Crofts Hummingbird just a slight improvement from the standard; mostly with the vocal harmonies.

Contrast 1/2 speed versions to BetterRecords.com premium selections of standard pressings. The two I bought from BR; Steely Dan Katy Lied and CSNY 4 Way Street, were very clean and sounded very detailed compared compared to record store versions I had. BR is very pricey, but offers the ability to send it back if you're not pleased.

As for 45rpm LPs; I have a few that I unknowingly bought (nothing on the cover said 45!)  these too have a nice detailed sound, but I don't have a standard version to compare them to.

Thank you for the feedback. I guess, it would come down to each recording so I will order the Police - Greatest Hits (thanks @willy-t ). 

As far as R2R, I don’t see much sense in copying Vinyl on to R2R. Both R2R and TT offer very different and unique tactile playback experience.

Whether "half-speed" or "45 rpm", the answer is the same. "It depends." I have some "45s" that sound like you are in the recording studio with the musicians. I have others that are inferior to or at least no better than their "33" counterpart. Ditto "half-speed." I will say the best "45's" are superior to the best "half-speeds", at least in my experience. But you have to listen to each in order to know what is worth buying. Much of this is gimmickry and marketing, as you find with the current trend of "180-gram" vinyl. A crappy recording cheaply stamped on a thicker piece of plastic just a thicker piece of crap. Until you listen, you don't know if you are getting the wonderful quality of vinyl or a cheap copy of somebody's CD. 

The half-speed-mastered LPs I have from the '80s (MFSL and CBS Mastersound) do sound better than the conventional LPs.  Of course, the MFSL were also pressed with virgin JVC vinyl and made from the original master tapes, so that also helped.  If anything, I thought the bass was fuller on the MFSL than on the conventional LPs, so I'm surprised at the comments that bass is negatively affected.  I wonder if this is just a relative perception because higher frequencies are enhanced, which may result in weaker-sounding bass.