Rare. Expensive. Hard-to-operate. Those are all descriptions of a cutting lathe, which vinyl mastering engineers use for making lacquer master disks—a crucial part of the vinyl manufacturing process. Nevertheless, such devices are highly in demand due to the resurgence of vinyl and the absence of any new lathes of that type being manufactured.
If you’re a Puremixer, you can watch such a lathe in action in Start To Finish - Ill Factor Episode 20: Cutting to vinyl with Dave Kutch and Mark Santangelo Part 1. In the video, Dave explains how a lathe works—and talks about the decisions an engineer must make to get the best results possible.
The Long Road
Dave explains that it took him five years to find a lathe—a custom Georg Neumann VMS 70 model from the 1980s—for his facility, The Mastering Palace. “I was so fortunate to know all the prime people in this part of the engineering world who knew where the few existing lathes were and where they existed,” Dave explains, “and they could do the repair work for me. But it still took five years. That was only the beginning. Once it was here, it took a year and half of completely remodeling and redoing it; pulling apart every unit, every transistor, and replacing every capacitor.”
The custom Georg Neumann VMS 70 cutting lathe at The Mastering Palace.
Dave said it was worth all the time, money, and energy. “It was a torturous year-and-a-half,” he says, “but thankfully, at the end of it, we have a perfectly functioning lathe that actually sounds better than the day it was made.”
Not only are the lathes rare, but it’s also hard to find experienced engineers to run them. Like many aspects of audio engineering, cutting master disks for vinyl is part science, part art form. Fortunately, Dave had Mark Santangelo, an expert cutter, already working for him.
Grooving Audio
One of the functions of the lathe in vinyl mastering is as a transducer (a device that changes one form of energy to another) because it takes the audio signal (soundwaves) fed into it and converts it into vibrations. Those vibrations cause squiggle-like movements in the cutter head, which cuts corresponding grooves into the lacquer disk.
Eventually, that lacquer master is used to create a master disk on which the grooves are convex rather than concave, which is used to press albums out of molten vinyl. When a listener plays a vinyl record on a turntable, its stylus and cartridge do the reverse, “reading” the grooves and converting the vibrations back into an electrical audio signal, which is then sent to an amplifier and speakers.
The cutting engineer can adjust controls on the lathe to regulate the width and depth of the grooves and the spacing between them. “A combination of the spacing and the depth affects your sound,” Dave says in the video, “both in volume and in sound quality.”
A standard 12-inch LP offers about 20dB less dynamic range than a CD-quality recording. It also has a lower signal-to-noise ratio, primarily due to mechanical noise from a turntable and hiss from the record itself.
The program length on a 12” LP is limited. The general consensus is that to maintain decent fidelity, an album should have no more than 23 minutes per side. The cutting engineer could fit more by reducing the space between the grooves, but doing so would lower the sound quality and the overall level.
As you get closer to the center of an LP, the fidelity diminishes slightly.
When deciding on the song order for an album that will be pressed in vinyl, the artist must take those length limitations into account, also factoring in that bass frequencies create larger grooves and stereo bass even more so. Overly bright material can cause distortion and sibilance. Phase issues on the master recording can cause the lathe to cut grooves that are deeper and steeper than normal, which can cause a listener’s needle to jump on the turntable.
Also of interest: the early songs on a side have better fidelity than the later ones. That’s because the closer you get to the end of a side, the smaller the disk’s diameter gets. That results in less vinyl-per-second being available. Grooves near the end of a side can get what’s called Inner-Groove Distortion, which slightly reduces quality.
The Vital Parts
Contemporary vinyl mastering starts in the digital domain, where the mixes for an album (or a single) reside before cutting. Dave does his mastering from Magix Sequoia software. All the EQing, compression or other signal processing gets completed before the master gets cut.
Dave’s session in Magix Sequoia shows a duplicated master file with a delay applied to the track feeding the cutter head.
The lathe has several major parts to it. The cutter head is V-shaped and has a tiny ruby stylus that does the actual cutting. It’s suspended over the platter, which is like a heavier version of a turntable platter. It holds and spins the lacquer disk. The platter contains a series of small holes through which suction is applied to the lacquer disk to hold it in place during cutting.
Inside the cutting head’s assembly is a tiny ruby stylus that cuts into the lacquer disk.
The suction comes from a vacuum built into the unit, whose attachment drops down into the center of the platter. Part of its suction is also directed to the surface of the lacquer, where it sucks up the excess material created when the head cuts the lacquer. The suction removes it from the surface of the lacquer from where it’s sent to a waste receptacle.
The highlighted area shows the holes in the platter through which suction is applied to the lacquer disk.
The pitch computer is another essential part of the Neumann lathe. In this context, the word “pitch” has a different meaning than in music. Here, it refers to the number of grooves cut per inch, not the frequency of a note. The pitch computer gets fed a duplicate of the audio sent to the cutter head. The latter gets delayed slightly so that the pitch computer gets it slightly earlier (sort of the analog version of a “look-ahead” feature.
The pitch computer calculates how wide the groove needs to be at any given point based on the incoming audio. It makes the cutting process more efficient and thus allows for more program time and better sound quality.
The Pitch Computer (shown here with its remote control) helps make the cutting more efficient.
