Why 45 rpm? by Kevin Gray, AcousTech Mastering
After 60 years the good ol’ analog LP is still one of the highest resolution sources of music distribution available. It has a solid, palpable, satisfying sound that no digital format has yet equaled, let alone surpassed. The most unfortunate thing about the LP is that it was really starting to flourish back in the mid 80s, just as the record companies tried to kill it.
Advances in cutterheads (the device that etches the groove in the master lacquer disk) and cutting electronics reached a pinnacle in the early 80s. Digital computers arrived on the scene in their best role: Out of the audio chain, but doing machine-control to adjust the groove spacing on the record for maximum playing time and recorded volume. 180 gram virgin vinyl pressings were the next development, and last but not least, around the late 70s, 45 rpm 12” LPs started to appear.
Why 45, you ask? Because it sounds better! In record mastering, the higher the recorded level and frequency, the greater the groove curvature. Curvature isn’t usually a problem, per se, on the outside of a 12” 33 1/3 record, but as the groove moves toward the center, its relative speed slows down and curvature increases. Yes, it is still turning at 33 1/3 revolutions per minute, but consider: one revolution takes 1.8 seconds. That 1.8 seconds at a 12” diameter is covering a lot more territory than at the minimum 4.75” diameter. The result is actually a loss in high frequencies, and increase in distortion as the groove moves to the center. The problems start when the curvature of the groove equals or exceeds the diameter of the playback stylus. What can be done about it? Many things have been tried, but there is no “magic bullet”. Keep the recorded volume to a reasonable level (read: On scale on the meters) is the first thing. Play the record back with an elliptical or line-contact stylus that has a smaller tip radius. And, if possible, make the record short enough to keep the music away from the very end of the disk. This isn’t always possible, of course.
BUT, if we spin the disk at 45rpm we now have a 35% increase in groove velocity at any point on the disk. This is a huge advantage! Yes, the groove still slows down as it moves inward, but the effects are greatly reduced. The only problem is that the amount of recorded time is now also reduced by 35%. What do you do about that? (Hint: split up the LP into 4 sides on 2 records.) Now you’re cookin’ doc! Yep, twice the mastering cost, plating cost, pressing cost, label and jacket costs. It’s enough to make the bean-counters break down and cry. But the sound! Oooooh, yeah! This isn’t sales hype, it’s physics. Listen for yourself. You tell me if it’s worth it. A lot of music lovers think so…and they are right!
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