General Question

blastoboy1000's avatar

Why is telephone (land lines and cellular) audio quality so bad?

Asked by blastoboy1000 (24points) January 2nd, 2011

To clarify, why does the audio of telephone calls have such a low bitrate? In case there are people who wonder whether the problem exclusively deals with issues regarding technological limitations, and is unaffected by business practices and regulations: Other forms of voice communication, such as those through computer hardware, have such higher voice quality, so why not telephone audio as well?

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5 Answers

Nullo's avatar

As best I can figure, the problem lies not in the data, but in the microphones and speakers in the handset. Generally, as the size of these diminishes, so does their quality. A dime-sized speaker is invariably going to sound crappy.
That, or the lines offer so little in bandwidth that high-quality sound is simply too bulky.
Or both.

filmfann's avatar

Also, the transmission often limits the sound to 3000hz, so you are not getting the fullness of the sound.

LuckyGuy's avatar

Human vocal cords vibrate from about 50 to 1000 Hz. The frequency content of speech is slightly higher than that. Humans (if they are under 25 and did not blast their headphones or go to too many concerts) can hear up to 20 kHz. Try adjusting the equalizer on your stereo to cut off anything above 2000Hz. The speech will not be as “bright” but will be perfectly intelligible. To optimize the number of conversations and information passed across a wire it was decided to limit frequency content to around 2500 Hz. Think of it this way. Let’s say you have 20kHz of bandwidth to use. Would you rather have one conversation at 20KHz or 10 conversations at 2kHz. The phone system picked the latter. That kept consumer costs low. For conversations that mostly consist of “Dude, wassup? Where are you? I’m here now, I’ll be there soon” is it really worth pay for 10x the bandwidth?

IchtheosaurusRex's avatar

Landlines operate at a maximum of 64KB/s, effectively limiting audio range to 4000KHz if you’re digital end to end. This is fine for voice, not so much for music. Cellular phones use packetized voice with quite a bit of compression. Statistical multiplexing can limit the quality of landlines even farther.

lochmeister's avatar

I’ve been trying to figure this out myself, its seeming that the transformers needed to produce frequencies below 200Hz would have made for very bulky devices. its cut off also at 3.2kHz which is why “s” is often confused “f” ass the definition to “s” is in the 6–8kHz range.

“The phone company decided years ago that the 180 Hz to 3.2 kHz range would be sufficient for speech intelligibility while allowing them to multiplex many calls over coax and twisted pair. Signal to Noise: Approximately 45”

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