Why, in the modern age of "HD" obsession do phone conversations still sound like you're listening through a tin can?

Question: It struck me as odd when I was listening to a call-in radio show last night. The hosts were having trouble hearing the caller, and rightly so, because she sounded like she was transmitting from Mars. Couldn't "they" employ some kind of EQ feature for voice? "Android. Now available with 'TrueVoice'^TM "

EDIT: I noticed a few people citing bandwidth issues. Is this because the conversation is "live?" I mean, I can stream HD video on my phone, but I assume it's only because buffering is involved.

Also, with the audio quality being inherently poor, couldn't one develop some kind of software that fixes the voice after the fact (like the EQ I had mentioned), or can you just not polish this particular turd?

Reasons:

It's a legacy due to cost. When we used the old analogue (POTS) phone system it was designed to work well enough to be intelligible, but no more than that because a slight increase in quality would have cost huge sums.

Then technology moved on and phones first went digital. When this was specified it turned out that a method of encoding speech as good as the previous analogue system could be achieved, so that was standardised upon.

At the time the digital voice links used a data rate of 9600 bits per second. Technology always gets cheaper, so when we were still using modems in pre-broadband days we were getting 56,000 bits per second which is enough for CD quality phone calls, but the standards had already been set, were 'good enough' and standards are best if they don't keep changing.

So the world stuck with a standard voice call using 9600 bits per second.

**This is the correct answer. Also, phone calls don't really need a high bandwidth. Latency is much more important. The target is to keep latency <200ms. Anything more than that is noticeable by the end user in the form of delays/jitter/that sound Neo makes after he takes the pill. On an internal VOIP network, it sounds like the person is speaking directly to you, because the network is configured with QoS to provide the bandwidth and latency for a great phone system.