For those still using analogue or digital phone systems, voice on ISDN circuits has a bandwidth of around 4000Hz. The audio from an analogue phone is sampled at 8000Hz, and because of the nyquist theorem, must be low-pass filtered to 4000Hz. So any frequencies in the audio beyond 4000Hz are lost. Interestingly, the human ear and mind are good at recognising human speech, so this is considered "toll-quality" voice, i.e. good enough to pay for. This is the reason why certain vocalised letters are difficult or impossible to tell apart on the phone. For example, the differences between B, P, T, C, etc. are almost entirely above 4000Hz.
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I agree with you. The music phone service provider use is never the best! Like you, when I switch to my calendar on iPhone and ask my caller to wait while I do that, it would be great to have one of my iPod tracks play to him until I pressed the green bar again to return to the call. Surely one could set that up independently of the phone service provider: just a matter of substituting my music choice for my voice until I clicked back off hold?? May 15, 2009 12:10 AM User profile for user: Tamara Tamara User level: Level 6 (13,735 points) May 15, 2009 4:39 AM in response to DavidJA In response to DavidJA
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