Dear friends: Nothing is perfect in audio that’s full of trade-offs on diferent subjects where half-speed recordings is no exception.
Many times we can hear a better quality sound in half-speed not because is half-speed but because its mastering process was made more carefully.
Here are some notes that I took from recording engineers over the net:
a half speed job is a bit more difficult than just dropping the speed, and few are actually equipped for it. It requires specialized electronics on both the cutting lathe as well as the tape machine. It’s tougher to make adjustments during mastering, as you can’t really hear what you’re aftually doing. Wow & flutter is also greater on tape playback equipment at lower speeds, and things like tape damage and edits become much more noticeable as they basically take twice the amount of time to pass over the tape head. These things can "stick out" on playback whereas they wouldn’t on a conventionally mastered LP.
the few that still do half speed mastering actually aren’t doing half speed mastering anymore for some reason...""""
""" Half-speed mastering is a two-edged sword. One one edge, for a response of 20-20,000, the cutterhead only has to go up to 10,000, so if there are any nonlinearities in the upper range, they will be greatly reduced. Plus, if you were going to, say, 30,000 Hz (and you can, with both analog masters and vinyl) you’ll have that much more "breathing room" up there.
On the other edge of the sword, and this is a pretty sharp edge, you have to apply only half the RIAA curve when cutting the lacquer, and that’s not always easy to do. Plus, now your response for 20-20K has to go down to 10 Hz. And to make things even more fun, the response of playback heads is slightly different at 15 IPS than at 30 IPS. That’s why, generally, you’ll find 15 IPS machines set to NAB, and 30 IPS machines running IEC. """
"""" I would add that half-speed mastering was invented for RCA’s CD4 Quadradisc LP pressings in the early 1970s, when they had to figure out a way to get the 30kHz subcarrier frequency into the grooves. By reducing the cutting speed in half, they could easily get 15kHz in there with no problem.
Somebody discovered that there were advantages to making regular stereo LPs this way, too, but as Mr. Stephens says above, this affected the RIAA curve, NAB tape playback EQ and a bunch of other stuff. I remember at the RCA cutting room I used a few times on Sunset Blvd. in the late 1970s (across from the Ceramic Dome), they had some black boxes that they would plug in-line when they needed to do half-speed mastering, plus some charts and notes on a bulletin board above the Studer A80s they used for playback """"
This is the response curve that actually gets cut into the groove. You can see that response is fairly even over only a short distance around 1,000 Hz. So for half-speed cutting, that entire curve has to be shifted down one octave, the "knee" at 500 Hz has to be lowered to 250 Hz, which when played back at normal speed would be shifted back up to 500 Hz. Which is just a matter of changing a couple of component values in the cutting amp. But, as was pointed out, you really can’t hear what effect the changes will have on the finished product until you play it. Theory is one thing, listening is another. """
""" The problems with the process are the same ones mentioned in this thread. All the equalizion had to be done trial and error in that you couldn’t monitor in real time. For records that didn’t need much help I never thought this was a big deal.
Steve and others have noted that the tonality seems to change when using 1/2 speed mastering. This may be, but when I was involved it was not my prime concern. After all, slight differences in tonality seemed like a small price to pay for the other benefits. To me, this was much like making backwards tape copies, which generally yielded better copies than straight copies """
So, the ball is on each one of us field.
Regards and enjoy the music,