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Have you ever noticed that a loudspeaker is
the opposite of an eardrum?

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Eh, probably not.

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But it’s true!

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See our ears work by concentrating changes
in air pressure onto a small diaphragm that

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will move back and forth with the pressure
changes.

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This vibration causes stimulation in the heary
bits of the ear which your brain can, assuming

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you have normal hearing ability, turn into
what we perceive as sound.

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A loudspeaker does the opposite--its diaphragms
(the driver cones) vibrate to create pressure

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changes in the air.

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This vibration gets transferred to our eardrums
so we can hear it.

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We’re sticking to simple stuff today because
the rabbit hole is just too deep.

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All you need to know is that things vibrate,
which causes air pressure to fluctuate, which

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causes our eardrums to also vibrate, which
stimulates the brain so that we can perceive

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that vibration as sound.

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This channel started as a series exploring
the history of artificial sound, and it’s

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been over TWO YEARS since I last touched on it at all.

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Finally we’re finishing this up with the
introduction of

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DIGITAL SOUND
(emphasis added with obnoxious reverb).

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Since it’s been forever, let’s go over
a brief history of sound recording technologies.

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The first device which could reproduce a sound
recording was the phonograph.

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Thomas Edison’s invention consisted of an
artificial eardrum, which would vibrate along

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with changes in sound pressure, and with the
aid of a collecting horn, the vibration is

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transferred into this stylus, creating an
up-and-down motion.

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This carves a groove into a wax cylinder,
and the vibrating stylus creates an imprint

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of the sound wave.

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The depth of that groove becomes a literal
analog of the original sound vibrations.

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Then, when the stylus is run over the now
bumpy groove, the bumps cause the diaphragm

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to vibrate in the same way as it did when
it first made the bumps, and the result is

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that you hear the same sound as before.

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Or at least, a barely passable imitation of
that sound.

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(sad sounding violin music)

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Commercially produced
discs and cylinders were molded from master

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recordings, and wouldn’t wear down like
the original wax cylinders.

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They were played back using devices like this.

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This device is called a reproducer, and
for decades all phonographs were based on

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simple acoustic devices like this.

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For nearly a century, this is how artificial
sound recording technologies worked.

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Something (like this horn) would collect sound
waves, and recreate them onto a physical analog.

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Then, that physical analog could recreate
the original sound waves when played back.

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While it all started with simple acoustic
devices like this phonograph, eventually improvements

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were made.

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The development of the electronic microphone
was perhaps the most important.

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Now, sound waves cause a receiving diaphragm
to move a coil of wire around a magnet, and

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a voltage is produced in the wire as the diaphragm
moves.

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This time, sound waves are recreated as a
voltage coming from the microphone, and by

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amplifying this voltage and sending it into
a new record cutting device which moves its

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cutting stylus as a function of the voltage
it receives, a more accurate carving of the

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sound wave could be made into a disc or cylinder.

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This greatly improved the fidelity of the
recorded sound, even on acoustic reproduction

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devices like this.

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With the proliferation of radio--which I feel
I must explain is a sound transmission technology,

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not sound recording.

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Just so we don’t get confused too much here--

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the loudspeaker became a big deal.

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Loudspeakers are the opposite of microphones--instead
of producing a voltage as a reaction to a

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sound pressure wave moving its diaphragm,
a loudspeaker will move its diaphragm and

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create a pressure wave as a reaction to incoming
voltage.

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With loudspeakers all the rage, record players
could now use a phonograph cartridge, which

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acts like a microphone for records.

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The movement of the stylus as the groove vibrates
it generates a voltage which can be amplified

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to drive a loudspeaker.

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This gets very meta very quickly.

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An artificial ear turns sounds into voltage,
and a cutting stylus turns this voltage into

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a groove on a record.

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Then, a playback stylus playing the record
generates a voltage as the stylus vibrates.

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This voltage is then amplified to drive a
loudspeaker, which causes pressure changes

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in the air around the loudspeaker, which your
ears concentrate down to your eardrums, and

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now your real eardrums are vibrating in roughly
the same way that the original artificial

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eardrum moved in the microphone in the first
place.

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Yeah.

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In essence, the record becomes a way to recreate
the original pattern of voltage created by

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the microphone, so that the sound can be heard
again in a different place

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at a different time.

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Let’s cut out the middle bit because that’s
what’s most confusing.

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A microphone like this creates an electrical
signal of fluctuating intensity based on how

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its diaphragm moves.

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I can just amplify that signal and send it
straight into a loudspeaker, which will reproduce

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the sound in real time.

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Radio accomplishes this wirelessly, but the
sound isn’t recorded.

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To capture the sound coming from the microphone
to be played back later, it has to be converted

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into an analog of the signal.

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And that’s why it’s called analog recording
technology.

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No matter if it’s a record, a cassette tape,
an open reel tape, or even a wax cylinder,

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the sound information is recorded “doorectly”...

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Doorectly.

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Doorectly?

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The sound information is recorded directly
onto something, which can then be used to

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recreate a copy of the original sound information.

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That something is an analog of the original
sound waves.

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Improvements in sound technology were for
many years simply incremental.

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Wax cylinders became shellac discs.

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Shellac became vinyl.

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Magnetic recording wire allowed for a reusable,
electronic recording medium.

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This was improved into magnetic tape, allowing
for a high fidelity, versatile recording medium

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enabling multi-track recording and editing.

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And to improve on the noise of magnetic tape,
different particle formulations were developed,

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and noise reduction technologies matured.

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But we were still just taking some signal
from a microphone, then slapping it basically

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as is onto some sort of physical medium.

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And that medium was never perfect.

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Poorly made tape would cause signal dropouts.

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Discs would be plagued by dust and scratches,
and would slowly wear down with each play.

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Because the analog medium contained the sound
in its physical properties, it was inherently

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prone to wear, damage, and distortion.

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Which of course would wear down, damage, or
distort the sound recording itself.

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If only there were some way to encode the
sound, perhaps a way to store sound logically

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rather than analogously.

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Maybe if the signal weren’t the sound itself,
but instead were a set of instructions on

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how to recreate it, we could get lossless,
near-perfect sound reproduction.

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And thus, digital sound was born.

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The heart of uncompressed digital sound is
pulse-code modulation, or PCM.

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PCM’s roots can be traced back to the telegraph
days, but its invention as we know it today

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for sound came from British Engineer Alec
Reeves.

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I feel I must compliment Mr. Reeves on his
given name, it’s excellent.

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Very good.

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He first devised this digital method of transmitting
and receiving voice communication in 1937,

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though it required extremely complex circuitry
for the time.

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However, PCM transmission was used during
World War 2 as a way to encrypt extremely

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important voice conversations, such as those
between Winston Churchill

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and Franklin Delano Roosevelt.

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This encryption system was called SIGSALY,

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“SIGSALLY”?

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“SIGSALIE”?

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Or Project X, X System, Ciphony 1, or Green
Hornet.

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Anyway, Project Green Sally X System Hornet
1 was much more complicated than simple Pulse

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Code Modulation, but PCM was a large part
of its encryption.

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So how does PCM work?

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It’s actually simpler than it might seem
at first.

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It’s rather like a system for repeatedly
asking what the instantaneous amplitude of

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a signal is many thousands of times per second,
then simply writing that down.

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Let’s look at a simple sine wave.

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If this were to be encoded on a vinyl record,
the groove of the record would start out straight

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in the center, then move to the left as the
signal intensity reached peak, then it would

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start to move to the right, keep moving, keep
moving, and then it would pull back to the

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center.

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When it’s played back, the movement of the
stylus as the walls of the groove wiggle it

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back and forth will recreate this signal.

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And audio tape does the same thing, except
the intensity isn’t recorded as a physical

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movement, but as a degree of magnetization
on the tape.

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But with PCM, we aren’t even trying to recreate
the wave.

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Instead, we want to quantify it and play connect-the-dots.

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Let’s say I want to take 20 samples of this
waveform.

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OK, I’ll divide it up into 20 chunks.

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Now I just need to define the detail I can
have within each sample.

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Let’s put this on a scale of 0 to 15.

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That's 4 bits of resolution.

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Now, at each sampling point, we can take the
closest value.

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This sine wave can now be represented as the
following string of numbers.

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To get the sine wave back, we simply plot
those numbers on a graph.

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Then, connect the dots.

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Tada! A sine…

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wave?

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Well, a sloppy sine wave.

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But that’s only because we weren’t very
specific.

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We only took 20 samples, and each one could
only be one of 16 values.

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But now we know the two most crucial parts
of digital sound--the sample rate and the

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bit depth.

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Perhaps the most common sample rate and bit
depth of digital sound is 44.1 kilohertz,

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16 bits.

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This means that every second, 44,100 samples
are taken, and each sample can be one of 65,536

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values, or 2 to the power of 16.

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And that’s how devices like this, a Tascam
DR-05, record sound.

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It’s looking at the voltage coming from
the microphone, and taking precise measurements.

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Every 44.1 thousandth of a second, it takes
a voltage reading, and, well, writes it down.

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It’s furiously quantifying and logging the
voltage it measures with 16 bits of accuracy,

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and the result is a string of numbers that
logically represent the shape of the sound

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waves that exerted pressure on the microphone’s
diagram.

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Pretty neat, huh?

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And it can actually write down two numbers
at a time, since this has two microphones

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and records in stereo.

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Inside this recorder is what’s called an
analog-to-digital converter, or ADC.

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The “ADC” is the actual device responsible
for creating the stream of samples.

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It takes the analog signal coming from the
microphones themselves and converts it into

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a stream of discrete numbers.

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If you open the files it makes in audacity,
you see what looks like a waveform of the sound.

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It is a waveform, but a waveform that’s
been plotted precisely on a graph.

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Zoom way, way, way in on the waveform,

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and eventually you can see the individual samples themselves.

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And that’s all digital sound is--

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it’s a huge list of numbers strung together in order.

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To get these numbers back into sound we can
hear, we need to use the opposite of an analog-to-digital

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converter, or “ADC”.

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So, we’ll use a DAC, or Digital-to-analog
converter.

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I like it when names make sense.

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A DAC will read the string of numbers, and
generate an analog voltage based upon their

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values.

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The DAC will smooth out the choppiness of
the samples a bit to make the resulting sound

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a little more natural, and now you’ve got
an analog signal to send into an amplifier

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and drive a loudspeaker.

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The result is a near-perfect reproduction
of the originally recorded sound.

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Here’s a very crude analogy to explain the
difference between analog and digital sound.

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A vinyl record’s walls generate an analog
signal by moving the stylus left and right...

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as well as up and down.

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It’s diagonally moved for stereo, but just
imagine for a moment that it’s just left

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and right.

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A record directly creates the analog signal
via the motion of the stylus.

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But a digital sound source is instead sort
of like a virtual stylus riding in a virtual groove.

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The sound samples are snapshots in time of
where the stylus was.

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A DAC will then create an analog signal by
running a virtual stylus through this virtual

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groove and placing it at exactly the correct
location--and thus generating the appropriate

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voltage level--as defined by the samples.

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By using a giant list of numbers to recreate
sound, instead of the physical properties

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of a plastic disc, the sound can be reproduced
flawlessly and accurately with no reliance

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on the record player’s cartridge properties,
the integrity of its stylus, it’s motor,

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the quality of the vinyl etc.

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The biggest boon of digital sound was that
it eliminated all of the little nuances that

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might change how a recording sounds.

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Digital sound is in a sense, absolute.

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But getting digital sound into the hands of
the average consumer took a long while.

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DACs and “ADCs” were expensive components,
and the amount of raw data generated by sound

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recording was immense for the standards of
the time.

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Although 650 megabytes, the data equivalent
of the first compact discs, is a paltry sum

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of data in the 21st century, it was unimaginably
huge in the early 1970’s, when the first

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commercial digital sound recording took place.

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For context, the Commodore 64, released the
same year as the compact disc, has 64 kilobytes

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of ram, and that was considered huge for the
time.

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A compact disc held roughly ten thousands
times as much data.

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64 kilobtyes of CD quality audio lasts this
long;

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(clip)

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That’s not super helpful.

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When we continue, we’ll look at the methods
that were used to store data from digital

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recordings, and we’ll discuss the rise of
the compact disc as a robust, consumer-friendly

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format for digital sound reproduction and
distribution.

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Thanks for watching, I hope you enjoyed the
video!

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If this is your first time coming across the
channel and you liked what you saw, please

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consider subscribing to Technology Connections.

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Don’t forget you can also follow me on Twitter
@TechConnectify, and you might enjoy the second

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channel, Technology Connection 2, where I
talk about stuff and don’t prepare for anything.

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Also, thanks to Lord Telaneo on Twitter, there
is also a Technology Connections Subreddit.

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I really don’t know reddit at all, but you
will also find me there as TechConnectify.

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As always, thank you to everyone who supports
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folks that have been scrolling up your screen.

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It is with the support of people like you
that I’m able to make these videos.

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Thank you.

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If you’d like to you join these awesome
people and support the channel too, why not

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take a look at my Patreon page.

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Thank you for your consideration, and I’ll
see you next time!