Future Tense: The Magic of Vinyl

Maximum PC Staff

There is genuine magic in a vinyl record.

Imagine it.  Here’s a diamond stylus racing through a vinyl groove, somehow turning all those little bumps and ridges into beautiful, stunning music.

First, consider the vinyl.  If the vinyl is virgin—never used before, not recycled—it’s a pure surface.  If it is recycled, it will have impurities, little lumps of dirt and dust and maybe some bits of shredded label too, and that will show up as a granular surface in the groove which will slightly degrade the overall quality of the sound.

Now think about the stylus, a precisely shaped triangle of diamond mounted on a precision cantilever made of aluminum, boron, ruby, diamond, beryllium, or even carbon fiber for stiffness—each with its own physical characteristics that will influence the quality of the sound.

One of the critical factors in playback is the shape of the stylus.  It needs an elliptical shape for the best contact with the sides of the grooves, but if it’s too large, it rides higher than the cutting stylus that carved the original groove from which the record is made and it won’t reproduce the sound as accurately.  If it has a bi-radial shape, with the tip of the stylus having a narrower radius than the main body, it can ride lower in the groove and more closely match the path of the triangular cutting head.  But if the cartridge rides too low in the groove, or has too much tracking force, it can bottom out and the sound will be degraded.

Finding the right tracking force for playback is a delicate dance with the laws of physics.  Most cartridges are designed for only a few grams of tracking force.  The less tracking force, the better.  Because the tip of the stylus is so small the pressure where it actually touches the groove is focused down to several tons.  Too much tracking force and the stylus can damage the groove.  Too little tracking force and the stylus will bounce out, and when it finds its place again that can also damage the groove.  So it’s a good idea to check tracking force regularly.  It’s also a good idea to check the stylus regularly for wear.  Even the best diamond stylus will begin to wear out after the first few thousand hours.

A worn stylus will produce audible distortion.  Even worse, it will irreparably damage the grooves as it tracks through them and that will produce permanent damage to the sound.  Actually, every playing of a vinyl record produces a small amount of wear on both the stylus and the vinyl.  It does add up.  And if there’s even the slightest speck of dust in the groove, the pressure of the stylus passing over it is enough to push that dust irreparably into the groove wall, producing a corresponding click or pop every subsequent time the stylus passes over it.  Unless you’re playing your disks in a clean room, you will eventually begin to hear a faint patina of crackling in the background of quieter passages.  Even with flawless cleaning and care, a vinyl disk can start to show audible degradation after twenty or thirty playings.

At the opposite end of the stylus cantilever, there’s either a magnet or a coil, depending on the design of the cartridge.  If it’s a magnet, its movements are sensed by a set of coils.  If it’s a coil, its movements sensed by a set of magnets.  Whichever design the cartridge contains, the result is a very faint electrical signal.  Actually, it’s two electrical signals, one for each stereo channel.  One side of the record groove is the left channel, the other side is the right channel.  Each side of the groove is ribbed with thousands of undulations per second.  As the stylus rides over these undulations, it vibrates in response.  The two sides of the groove create their respective vibrations 90 degrees apart.  The detecting magnets and coils are also 90 degrees apart so they each pick up only their respective channel.  They’re so precise and sensitive that crosstalk between the channels can be reduced to a barely audible 35 decibels.  Some post-processing can reduce this even further.

The tonearm is also part of the sonic equation.  It adds its own weight and mass to the playback process, of course, but there’s another factor to be aware of too.  Record masters are produced by a precision mechanism that moves the cutting stylus linearly—the cutting head moves across the record in a straight line.  A good cutting head will have 400 watts of amplifier power so as to accurately trace a physical representation of the sound waves into the surface of the master.  It has to be able to trace 20,000 separate cycles of sound into each groove wall, although in practice, most records start to roll off around 15,000 cycles.

Now, once you get the resultant disk onto a turntable, most playback arms are anchored at one end and swivel across the record, describing an arc.  This means that at the outermost and innermost grooves, the playback stylus is actually at an angle to the way the grooves were cut.  It’s not severe, only a few degrees, but on that scale it does affect the sound.

More serious is ‘pinch effect.’  At the outer edge of the record, the two walls of the groove will look equal to the stylus.  But as the groove gets closer and closer to the center of the disk, its curvature becomes more and more pronounced and there is actually less room in the groove for the various undulations, particularly the very fine ripples that produce the high notes.  Golden-eared audiophiles are quite good at recognizing the ‘pinched’ quality of the sound.  The dynamic range is often reduced on the inner grooves.

If the vinyl record is too thin, it could warp.  If it has not been properly cared for, it will most certainly warp—and even the slightest warp will influence the sound of the playback.  If the warp is pronounced enough, you’ll hear it as a kind of muffled thumping.

The turntable’s accuracy is critical too.  Most quality turntables have stroboscopic reference dots.  If they’re moving one way, the platter is too fast.  If they’re moving the other way, the platter is too slow.  There’s also the issue of the turntable’s motor.  Some audiophiles feel that the direct drive has better speed stability, but others argue for a belt driven platter because it has a complete acoustic decoupling of motor and platter.

A turntable that doesn’t maintain precise speed will produce ‘watery’ sounds, most noticeable on piano music.  This is called ‘wow’ and ‘flutter.’  (Wow and flutter are also present if the source tape is played back unevenly, or if it has stretched on the reel.)  A turntable that doesn’t have good acoustic decoupling will produce ‘rumble.’  The vibration of the motor will be transmitted through the vinyl into the stylus.  A belt-driven turntable is pretty much immune to rumble, but if the belt stretches or wears, speed accuracy will be affected.

Any vibration at all, any variation in speed, any rumble, will be transmitted to the cartridge and will affect the signal.  The very faint electrical impulses travel through some very fine wires (with their own specific impedances and resistances that can affect the signal) through the tonearm, into some much thicker wires (which also have specific impedances and resistances) which take the signal from the turntable to a preamplifier.  The preamplifier boosts the very faint electrical signals produced by the motion of the stylus up to the level required by the amplifier.  The line-level output of the preamp goes into the line input of the amplifier.  (If you have a receiver, the preamp is built-in, but this is what’s going on inside.)  If any part of the signal path is not properly grounded, a faint but noticeable 60-cycle electrical hum will be added to the signal.

The preamplifier also applies what is called an RIAA equalization curve.  When the record master is cut, the highs are boosted and the lows are decreased.  This reduces the back and forth undulations of the groove, so that the stylus can stay in the groove when it hits loud bass passages—like the cannons in Tchaikovsky’s 1812 Overture.   When the record is played back, the RIAA equalization curve compensates by lowering the highs and boosting the lows back to their original levels.  If the equalization is applied accurately, there should be no audible effect.

The amplifier further amplifies the electrical signals.  Depending on how much wattage is available to the amplifier, the signals can be boosted enough for even a heavy-duty speaker.  Speaker-design is another whole set of issues.  But if the amplifier is unequal to the task, the peaks of the signal will be clipped, producing a very unpleasant and harsh distortion.

There are other distortions that also affect sound quality.  Intermodulation distortion which occurs at the sum and difference frequencies of the original frequencies, harmonic distortion where the harmonics of some frequencies interfere with others, phase distortion where the two channels are out of phase resulting in vague unfocused sound sources, frequency response distortion when the levels of different frequencies are inaccurately or inappropriately filtered, and a faint grainy distortion that lurks in the analog master tape and is only audible when all the others have been minimized.  There are probably a few others that I’ve forgotten to mention.

You will need the best possible electronics throughout the signal path to reduce all of these distortions to inaudible levels, but the amplifier that actually powers the speakers will be one of the most critical components.  Many golden-eared audiophiles say that transistor-based amplifiers produce a harsh sound, they insist that only a tube amplifier will have the necessary warmth and clarity for good musical reproduction.  (Bob Carver demonstrated as early as the eighties that with meticulous tuning of the separate components a transistor-based amplifier could match the sound of a tube amplifier, but the argument continues anyway.)

At its very best, the frequency response of a vinyl record should be 20-20khz.  (20 cycles per second all the way up to 20,000 cycles per second is the classic definition of a high-fidelity signal, with a frequency response that’s flat within 1 or 2 db.)  But many vinyl recordings start to roll off at 15,000 hertz.  Most people won’t hear the difference, because the hearing of most listeners also starts to roll off at 15khz.  Those who subject themselves to very loud music with headphones, earbuds, or raves, will likely have even more high-frequency impairment.

The dynamic range (signal-to-noise ratio) of a vinyl record can be as much as 60 decibels although 50-55db is much more common.  Dynamic range is the difference between the loudest and softest sounds, but most vinyl records are compressed to less than that range, partly to conserve groove space and partly because if listeners turn up the sound to hear the quieter passages, they’ll hear the ‘noise floor’ as a kind of granular hiss.  Compressing the signal is a necessity in vinyl because it allows the engineer to have most of the sound loud enough to keep the noise floor below the threshold of audibility.

When all of the equipment works the way it’s intended—especially if you’ve invested tens of thousands of dollars in state-of-the-art equipment that can address all of various factors listed above (as well as the more arcane ones I didn’t mention)—you can get some incredible sound out of a vinyl record.  (I mean, like totally awesome, dude.)

That’s why the vinyl record is sheer magic.

It’s the triumph of passionate will power over the inordinate obstinacy of the physical universe.

David Gerrold is a Hugo and Nebula award-winning author. He has written more than 50 books, including "The Man Who Folded Himself" and "When HARLIE Was One," as well as hundreds of short stories and articles. His autobiographical story "The Martian Child" was the basis of the 2007 movie starring John Cusack and Amanda Peet. He has also written for television, including episodes of Star Trek, Babylon 5, Twilight Zone, and Land Of The Lost. He is best known for creating tribbles, sleestaks, and Chtorrans. In his spare time, he redesigns his website, www.gerrold.com

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