WEBVTT
Kind: captions
Language: en

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If you're on hold to a company, and they're
playing music down the phone at you,

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the chances are it sounds terrible, and sometimes
it just dissolves into static.

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Telephone signals are not designed to carry
music, and to explain why,

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we have to start way, way back
with old telephone equipment like this.

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Early telephone calls were put through by
a human operator

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who would be literally connecting the two
phone wires into one circuit

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at a big board of switches.

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Or a "switchboard".

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Any sound at one end,
whether it's speech, music, whatever,

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would be converted to an electrical signal,
sent down the wire,

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and converted back at the other end.

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You send music, you receive music --

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although it'd be limited by the abilities
of the tiny microphone and speaker.

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But telephone exchanges like this only work
for small numbers of connections.

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Because, you know,
you can't do this for every call.

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[PHONE RINGS]

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Phone companies quickly realised
that they could save

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on setting up thousands of wires
between exchanges miles apart

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if they were able to put several conversations
down one wire at the same time.

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So rather than transmit every frequency of
sound in the original signal,

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they would cut off the high and low frequencies,

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the ones we don't absolutely need to understand
speech,

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and then they would shift each call into a
different frequency band.

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At at the other end, like tuning in a radio,

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they would shift each call back to the right
frequencies so you could hear it.

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I mean, the quality wasn't great, but it was
good enough.

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And hey, we got cheap long distance calling.

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We got used to that phone-quality sound.

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[EXCHANGE CLICKS]

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And it became the standard.

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So already [PHONE RINGS] music was going to
sound a bit dodgy,

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with all the high and low
frequencies cut off.

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But while we were still running
on analogue circuits

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[EXCHANGE RESETS]

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it wasn't going to sound like static.

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That was the fault of computers.

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Phone companies realised that they could send
even more calls down the same wire,

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or into the same airspace on a cellular network,

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if they used computers to compress the audio.

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And the more they compressed it,

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the more calls they could fit
at the same time,

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and the cheaper it'd be for them.

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These days, there is enough power
in pretty much everyone's phone

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to compress 4K video in real time,
but back then, not so much.

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MP3s had only just been invented,
and these do not have enough power

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to compress those.

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The standards for phone calls, even today,
rely on quick-and-dirty compression

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built decades ago, designed to run
on very little computing power,

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and optimised for speech.

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That compression is great at encoding one
clear voice --

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but chuck a load of complicated music at it,
with all its instruments

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[COMPRESSED MUSIC]
and it's going to sound bad.

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But not quite enough to break down into static.

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There is one last piece of the puzzle.

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Someone else cutting corners.

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Because in the worst case, that hold music
isn’t just compressed

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by the phone company on its way to you.

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It’s already been compressed
by a completely different system

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as your call bounces around a company’s
internal phone network.

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An internal phone network that has
probably been built by the lowest bidder.

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So the phone company takes
that already-mangled signal

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and mangles it in a different way
as it travels to you.

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And in a really badly designed system,

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maybe there’s an entire third layer
of terrible compression

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from whichever other company
runs the call centre

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that you're actually talking to,
off in some other country.

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[MUSIC RISES]
Speech can survive that chain

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But music...

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[MUSIC TURNS TO STATIC]
...music can't!

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Thank you so much to all the team
at the Milton Keynes Museum

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and their Connected Earth gallery,

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where pretty much all this
telephone exchange equipment

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is just open to play around with.

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Pull down the description for more about them.

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This is not a TARDIS.

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This is literally just
a police telephone box.