Record players have made a comeback over the past decade. Some
of the credit probably goes to the hipster trend toward retro
everything, but music lovers often claim records just sound
better than digital music. I played my part in boosting record
player sales after finding my mom’s old record collection in my
parents’ house. The collection itself was not particularly
exciting, but the possibility of listening to the exact records
she had played as a teenager felt like some sort of time travel.
So we bought a record player. I distinctly remember playing The
Beatles’ Sgt. Pepper’s Lonely Hearts Club Band. I had dutifully
met the college student stereotype of blasting The Beatles on a
regular basis, so I had heard those songs a hundred times. But
when the cacophony at the end of “A Day in the Life” came on, it
was not the one I had heard before. It sounded much deeper and
fuller, like there were new noises in it. I was skeptical of the
claim that vinyl sounded better, so I was surprised to be
hearing a difference. Being a scientific-minded person, I’m not
exactly swayed by one data point, but the experience did pique
my curiosity.
So what’s the deal with the vinyl phenomenon? Is it really
possible that records just inherently make a fuller sound? To
have any hope of answering these questions, we have to start
with something more basic: What is sound and how do we hear it?
All sounds are just vibrations in the air. You have likely seen
sound visualized as a graph with many peaks and valleys. This
graph is called a sound wave, and it shows how compressed the
air is at a given point over time. Air disturbed by some noise
source is funneled through the ear canal to a thin membrane
called the eardrum. The vibrating air causes the eardrum to
bounce back and forth in the same pattern as the disturbances in
the air, and this pattern is sent to the brain to be interpreted
as sound.
The human ear inspired the first audio recording device,
invented in 1857 by Édouard-Léon Scott de Martinville. The
machine was called a phonautograph. A horn played the role of
the ear canal, taking air down to a thin piece of parchment.
Like the eardrum, the parchment oscillated when vibrating air
passed by it. But in the phonautograph the movement was
transferred from the parchment to an attached stylus. A piece of
paper then recorded the drawings made by the stylus. Each step
of this process is a physical transfer of vibrations from one
medium to another, so the end result is a curve showing the
changes in air pressure that created the original sound. The
fact that the drawings could contain enough information to
reproduce the recorded sound did not appear to occur to de
Martinville or his colleagues, but it’s hard to fault them for
not immediately assuming a squiggle on a page could be used to
reproduce complex sounds.
Analog playback came around in the 1870s, when French inventor
Charles Cros had the ingenious idea to transfer the
phonautograph recordings to a groove on a disc. If you zoom in
on a single groove of a vinyl record and look at it from the
side, the shape would resemble one of the phonautograph
drawings. To play back the sound, the phonautograph’s process is
reversed. A thin point, such as a needle, rides along the
groove, moving up and down with the peaks and valleys encoded in
the record. The needle is held by an arm, and the needle’s
movement re-creates the same motion the stylus made during the
original recording. This arm is then attached to a thin piece of
some flexible material, which vibrates back and forth as
dictated by the arm’s motion. The movement of the material
disturbs the air, and the disturbances are amplified as they
flow out of a horn. The vibrations in the air created by this
play back method are the same as those that produced the
original recordings. Because our ear interprets sound based
entirely on the patterns of compression in the air, we hear the
exact same sound that had been recorded.
The mechanics of this process seem reasonable enough. Sound is
defined by vibrations in the air. Disturbed air makes the
phonautograph move in a particular way. Re-creating that motion
makes still air vibrate the way it had before, so the same sound
is reproduced. But tucked into this process is the entirely
unintuitive claim that everything from David Bowie to Nina
Simone to nails on a chalkboard can each be reduced to a single
squiggle on a recorded groove.
If we want to figure this out, we need to know how the brain
decides what listening experience to produce. Two key decisions
the brain makes are what volume and pitch you will hear. Volume
depends on the size of the peaks and valleys of a sound wave
(which is called amplitude) and pitch is determined by how many
peaks pass by your ear over the course of a second (which is
called frequency). The larger the amplitude, the louder the
noise; the higher the frequency, the higher the pitch. A band
playing their hit song won’t produce sound waves that are
uniform enough to easily pick out amplitude or frequency, but
that’s okay. Sound waves with uniform amplitude and frequency
are called pure tones, and these readily translate to some pitch
and volume.
Of course, if a piano and a violin play the same high C at the
exact same volume, there is still some quality that feels
different between the two notes. It turns out that pure tones do
not occur naturally, and when a piano or violin produces a high
C, the sound wave is made up of a specific combination of
different pure tones. The different amplitudes and frequencies
have nice relationships with one another, which is why you hear
a specific note rather than a mess of clashing noises, but the
single pitch you hear does not correspond to a single frequency.
The hard-to-define quality of sound that allows you to identify
what instrument you’re listening to is determined by the exact
combination of pure tones. When different instruments all play
at the same time, the various pure tones add together to create
the music you hear.
So what do pure tones have to do with the groove on a record
being able to tell David Bowie and Nina Simone apart? It turns
out that any curve can be written in exactly one way as a
combination of curves with uniform amplitude and frequency. In
other words, the single squiggle captured in the groove of a
record player can be written as a combination of pure tones. And
there is only one combination that will produce any particular
squiggle. The tool that makes this possible comes from
mathematics and is called the Fourier transform. Combined with
the fact that the sound we experience is determined by the exact
combination of pure tones, this bit of mathematics explains how
the vinyl record groove can completely determine the music you
hear.
When it comes to storing sound as a digital file, however, the
limited capacity of computers is a problem. Sound waves contain
an infinite number of points. Computers cannot store infinite
amounts of information. Digital music storage is possible,
thanks to the work of mathematicians in the 1930s that produced
the sampling theorem. According to the theorem, it is possible
to completely rebuild a sound wave using a finite number of
points—as long as they are close enough together.
There is one catch: The theorem requires that when the Fourier
transform breaks down the curve into a combination of pure
tones, all the frequencies fall between some maximum and
minimum. How close together the points on a curve need to be in
order to rebuild it depends on the distance between this maximum
and minimum. Because humans only hear sounds within a certain
range of frequencies, we can get rid of any other frequencies
that may show up in a sound wave’s decomposition and still get
back the original sound. So the sampling theorem explains how to
use a finite amount of information to store any sound wave.
Because mathematics describes an idealized version of reality,
the reconstruction of a sound wave from a digital file may not
perfectly match the vibrations of the sound itself. On the other
hand, analog recording is purely physical. Does this mean analog
is more accurate? No, it just means it’s different. Movement,
dust or scratches can change the sound an analog player makes,
and the recording process is similarly sensitive. The sound wave
produced by analog playback could be further from the original
than a good quality digital file would be.
Sound quality depends on a lot of factors, and it is impossible
to definitively state that either analog or digital is
fundamentally better. These days, many records are made using
playback of a digital file, so vinyl preference cannot be
attributed solely to the differences in the way the sound wave
is reproduced. But the fact remains that analog captures a
physical process whereas digital uses mathematics to reduce the
process to finite bits of information. What, if anything, is
lost in that reduction is difficult to pinpoint. But the
limitations of math in replicating reality may factor in to the
difference in listening experiences reported by so many vinyl
lovers. |
