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

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

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

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

  • Early telephone calls were put through by a human operator

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

  • at a big board of switches.

  • Or a "switchboard".

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

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

  • and converted back at the other end.

  • You send music, you receive music --

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

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

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


  • Phone companies quickly realised that they could save

  • on setting up thousands of wires between exchanges miles apart

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

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

  • they would cut off the high and low frequencies,

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

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

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

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

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

  • And hey, we got cheap long distance calling.

  • We got used to that phone-quality sound.


  • And it became the standard.

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

  • with all the high and low frequencies cut off.

  • But while we were still running on analogue circuits


  • it wasn't going to sound like static.

  • That was the fault of computers.

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

  • or into the same airspace on a cellular network,

  • if they used computers to compress the audio.

  • And the more they compressed it,

  • the more calls they could fit at the same time,

  • and the cheaper it'd be for them.

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

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

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

  • to compress those.

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

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

  • and optimised for speech.

  • That compression is great at encoding one clear voice --

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

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

  • But not quite enough to break down into static.

  • There is one last piece of the puzzle.

  • Someone else cutting corners.

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

  • by the phone company on its way to you.

  • It's already been compressed by a completely different system

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

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

  • So the phone company takes that already-mangled signal

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

  • And in a really badly designed system,

  • maybe there's an entire third layer of terrible compression

  • from whichever other company runs the call centre

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

  • [MUSIC RISES] Speech can survive that chain

  • But music...


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

  • and their Connected Earth gallery,

  • where pretty much all this telephone exchange equipment

  • is just open to play around with.

  • Pull down the description for more about them.

  • This is not a TARDIS.

  • This is literally just a police telephone box.

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

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B1 INT music telephone compressed static sound compression

Why Hold Music Sounds Worse Now

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    林宜悉 posted on 2020/04/01
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