So you think you know the cassette tape, eh?
That 80s and 90s crappy-sounding barely tolerable
thing we had before CD’s?
The ones that got eaten by your car all the
time?
The thing hipsters are pretending to listen
to?
Whatever memories you have of the cassette
could probably use some refreshing.
They don’t sound awful, they’re actually
much older than you think, and they’re backed
by some interesting technology.
Let’s have a look.
The cassette tape is actually a product of
the 1960’s, though it took some years for
them to take off.
The official name for them is the Compact
Cassette, and it was the Philips company that
invented them in 1962.
They aimed to solve two problems, neither
of which had anything to do with music.
Magnetic tape was not a new thing in 1962,
and reel-to-reel tape recorders were fairly
widespread.
But the machines weren’t very portable,
and even those that tried to be were still
plagued by the problem of tape which required
being manually threaded.
In the professional recording studio, these
weren’t problems.
The machine would just sit in one spot in
the studio, and having to be threaded manually
wasn’t a hassle compared to all the other
hassles that accompany recording music.
But people saw uses for magnetic tape outside
the recording studio, particularly in recording
speech.
In those days, men weren’t really expected
to know how to type.
The big-wigs in offices had secretaries to
type their letters for them.
But secretaries had this annoying habit of
leaving at the end of the day, thus being
unavailable to use their stenographic skills.
Machines like the dictaphone allowed these
corporate luddites to record their speech
at their whimsy so someone else could write
it out later.
The problem with the dictaphone was that it
used non-reusable cylinders or belts, and
mistakes couldn’t be fixed without some
sort of added note marking them as a mistake.
Magnetic tape, though, could be reused and
recorded over, since the magnetic signals
recorded on the tape could be erased.
Mistakes were easy to correct, just back the
tape up and record over the mistake.
But with large reel-to-reel machines and their
open reel tape, you weren’t about to see
them in an office setting.
The compact cassette fixed that right up,
though.
A number of clever innovations made for a
practical, portable tape format.
The most important innovation was the cassette
itself.
Instead of having an open reel of tape, the
tape is sandwiched in a shell of plastic with
access holes at the bottom of the cassette.
The tape was pre-threaded in the shell, and
the holes in the middle of the cassette allow
the machine to wind the tape with special
spindles that mesh with these cogs.
Having the tape contained so that you didn’t
have to touch it meant that the tape could
be much thinner.
With open reels of tape, since grubby little
hands are always fiddling with it, it can’t
get too thin or it will break with handling.
But inside a cassette where it won’t get
touched (or at least, shouldn’t get touched),
it could afford to be thinner and thus you
could pack a longer length of tape inside.
The bottom portion of the cassette is wider
than the rest, and it has a standard pattern
of holes that are very important.
These are what allow the cassette recorder
to interact with the tape.
Cassette recorders work fundamentally the
same as a reel to reel recorder, but since
we’re using a cassette the machine interacts
with the tape a little differently.
Let’s take a step back and look at a reel
to reel machine to see how ordinary tape gets
recorded.
The parts that interact with the tape are
called the transport.
A reel-to-reel recorder has 2 spindles that
hold the tape reels, and the transport sits
between them.
When using the machine, a full reel of tape
is placed on the left, and then the tape is
pulled out and through the transport before
being wound onto the empty reel.
The tape passes three heads, first an erase
head, then the record head, and finally the
playback head.
Lastly, the tape goes through the capstan
and pinch roller, which are the parts that
actually pull the tape past the heads.
The capstan is one of the most important parts
because it regulates the speed of the tape.
The pinch roller, a small rubber wheel, squeezes
the tape between itself and the spinning capstan,
and this is what actually moves the tape.
The reel on the right only rotates to spool
the tape onto the reel.
See, if I stop it, the tape doesn’t stop
moving through the machine.
Also important to note is the curved path
of the tape as it passes the heads.
This ensures that it stays tightly against
the heads, and various tape guides make sure
it stays in alignment as it passes them.
If you look at the parts inside a cassette
deck, you’ll see that they’re fundamentally
the same, although smaller.
There’s an erase head to the left, a record
and playback head in the middle (cassettes
use one head for both functions), and the
capstan and pinch roller are on the right.
But you might notice some problems that come
about with the cassette.
The capstan--it needs to be on one side of
the tape, and the pinch roller needs to be
on the other.
The tape has to somehow get between them.
How’s that supposed to work when the tape
is trapped in a box?
Well, that’s what the holes on the side
of the cassette are for.
See how the capstan is shaped almost like
a spike?
The capstan goes through this hole and thus
ends up behind the tape.
Then the pinch roller can move upwards and
squeeze the tape against the capstan.
Which brings us to the holes on the bottom
of the cassette.
Rather than bring the tape to the heads, the
cassette brings the heads to the tape.
The three holes on the bottom are shaped and
sized so that the erase head, play head, and
pinch roller can all fit neatly inside the
cassette shell.
The mechanism of the cassette deck lifts these
three components together inside the cassette.
A felt pad sits inside the cassette shell,
and it helps keep the tape against the head.
The pad is glued to a metal brace that acts
like a spring, making sure that the pad pushes
firmly on the tape.
When recording, only half the tape is actually
used.
This head is aligned with only one side of
the tape so that the tape can be turned round
at the end and run in the opposite direction
for a second side.
Part of what made the cassette successful
was its simplicity.
In many recorders, the buttons that you pressed
were physically linked to the mechanism.
This sony stereo is a great example.
This cassette recorder actually holds the
tape upside down.
The play button is directly connected to pinch
roller and heads, and the act of pushing down
on the button is what actually pushes the
heads into the tape.
In conventional cassette decks, the buttons
are instead levers that sit underneath the
cassette door.
They’re often called piano keys, and they
did just what this button does.
The only reason this cassette recorder holds
the tape upside down is so that the buttons
could be on top.
Higher end machines like this use automatic
mechanisms to move the components around,
rather than directly connect those components
to the buttons.
These were called soft touch controls, and
when cassette decks started to get microcomputers
inside controlling them, the buttons could
be placed anywhere on the machine, and these
machines were said to have full logic control.
Now that we understand the mechanical elements
of the compact cassette, let’s examine the
technical details.
At the time of the cassette’s introduction,
standard audio tape sounded pretty awful at
the slow speed of 1 and seven eights inches
per second.
Here’s an example of what that sounds like:
This speed wasn’t very good for music, but
it was fine for speech.
See?
I’ve run this sound through the tape recorder
and inserted it here.
It may not sound as good as before, but you
can still understand me just fine.
So this was the speed chosen for the compact
cassette.
The slow speed allowed for recording times
of up to 60 minutes per side on the cassette,
which was a great benefit for recording memos.
Now the corporate luddites we talked about
earlier could record their letter to Professor
Frederick, pop the cassette in an envelope
for inter-departmental delivery, and the ladies
in the transcription department would type
up the letter and send it back for approval.
What a weird time we used to live in…
But that was it.
That right there is what Philips invented
the cassette for.
8 track cartridges were just coming out, and
they seemed fine for music.
No need to improve the cassette.
OK, there actually was a need.
The 8 track was a weird format plagued with
issues, and wouldn’t last.
Now we had the problem of how to get the cassette
ready for music.
The slow tape speed wasn’t gonna allow for
decent music.
Well, it might not have in 1962, but by the
1970’s the actual tape was improved so much
that the slow speed wasn’t an issue.
Cassettes had roughly the same fidelity as
the 8 track by the early 70s.
But then there’s another issue.
We want stereo!
To get stereo sound on the cassette, the tape
had to be split into 4 tracks.
2 in one direction, and 2 in the other.
These narrow tracks were kept compatible with
older mono equipment because they were right
next to each other, and they’d work together
for a mono signal.
But they also introduced a problem.
The signal to noise ratio of the tape suddenly
became much worse.
Having a narrower track meant that the signals
recorded onto the tape became weaker compared
to the background noise.
But Dolby noise reduction would save the day
and bring the noise back in line, in fact
improving noise beyond what it was originally.
Here you’ll find a separate video explaining
how Dolby Noise Reduction works.
By the 1980’s, the cassette was well established
as a music format.
And they sounded really good.
Have a listen:
I bet you didn’t think the cassette sounded
that good.
Well, that’s just the tip of the iceberg.
That recording used normal tape, which uses
ferric oxide as the magnetic medium.
Cassette recorders equipped with adjustable
bias circuitry could also record onto chromium
tapes and metal tapes.
These special tapes were designated type 2
and type 4, and they sounded even better.
A type 2 tape uses chromium dioxide as its
medium, and this can hold more signal than
standard type 1 tape.
It required that the machine record with a
higher bias frequency and more volume, but
the resulting recording had a superior signal
to noise ratio than standard tape.
Type 4 tape was fairly expensive and used
pure metal particles.
These could hold a lot of signal, but only
higher-end cassette decks could record onto
them.
Metal tapes sounded better than vinyl records,
and indeed they sound just as good as any
CD, provided you’ve got a good enough tape
deck.
So we have type 1, 2, and 4.
Astute viewers may have noticed we skipped
3.
Type 3 tapes used a mixture of chromium dioxide
and metal, but they really never took off.
They’re so uncommon you’ll probably never
find a machine with a setting to use them.
The types of tapes have notches on the back
so that higher end machines could tell them
apart automatically.
Right next to the write-protect tab is another
notch indicating that this is a chrome tape.
Metal tapes have yet another notch closer
to the center.
Sensors in the tape deck would detect these
notches and adjust the record parameters automatically.
This deck, though, has a manual selector switch.
Let’s listen to the difference each tape
type makes.
Here’s the same song recorded with the same
level on each of the three tapes.
Because people are so lazy, auto reverse became
a priority.
Early machines used elaborate mechanisms to
actually remove the cassette from the transport,
flip it over, and then put it back.
These were quickly superseded by machines
that used a rotating head.
When the tape was playing in the forward direction,
the heads would sit like any other deck.
But when the tape got to the end, they heads
would quickly flip around and then the tape
would start moving in the other direction.
The change in direction happened due to a
pair of capstans which turn in opposite directions.
Depending on the direction selected, the pinch
roller corresponding to that direction would
come up and squeeze the tape against the capstan.
Interestingly, Nakamichi, the fairly undisputed
champion of high quality cassette decks, returned
to a mechanism which actually flipped the
tape around because of concerns that the rotating
head mechanism could over time bring the heads
out of alignment.
Whether or not this happens in practice is
up for debate.
Part of why the cassette took off was that
it was so portable.
The Sony Walkman was the first portable cassette
player, and it was introduced in 1979.
Later models like this one would add dolby
noise reduction, tape formulation selection,
and even auto reverse.
All in a machine barely larger than the tape
itself.
In fact, one walkman was smaller than a cassette,
and the machine expanded around it when playing.
One interesting note here is that auto reverse
walkmans actually have 4 heads.
When playing in one direction, the heads listening
to the other side are muted and you only hear
the forward heads (the other heads are listening
to side B backwards).
Then when the it got to the end of a side,
it switched pinch rollers, thereby reversing
direction, and then switched electronically
to the other set of heads.
I’ve often wondered why Nakamichi didn’t
just do this, with 4 heads and a miniature
erase head like this conventional auto reverse
machine has on each side.
The cassette died a slow death into the 2000s.
It stuck around in car stereos for a while
since road vibrations didn’t affect tapes
like they did CDs, but eventually they pretty
much faded away.
The cassette never really disappeared though.
It’s not really dead, and in fact is receiving
somewhat of a revival.
I admit I like the ability to make a mixtape
(the modern equivalent being a playlist) and
have a physical thing that contains the music.
And they do have a retro quality to them that’s
hard to replicate with a playlist on a smartphone.
Thanks for joining me on Tech Explorations.
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