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.
The most common codecs are G729 (compressed) and G711 (non-compressed). They are designed to compress human speech, and often cause a loss of audio fidelity — which is worse in some languages than others. On hold music that has been specifically designed for that purpose, to be used with VoIP systems and codecs, can sound great. But it is not easy to come by.

Not only can DoNotPay help you get in touch about cancelling subscriptions, scoring refunds or retrieving information, it’s like “a body camera for customer service calls,” Browder says. “Before they make a decision that rips off the customer, they’ll think ‘this could be made public and go viral and hurt our business.’ ” For example, an airline that jacks up prices for rescheduled flights surrounding hurricanes could be shamed for profiting off of natural disasters. Customer service disputes where it contacts companies about refunds for Comcast bills, delayed flights, etc. The free trial credit card that auto-cancels subscriptions before you’re actually charged Traffic and parking appeals where it generates a letter for you based on answers to questions, like if signs were too hard to read or there was a mistake on the ticket Hidden money discovery that finds refunds in your bank fees, identifies forgotten subscriptions, gets you free stuff on your birthday and more Government paperwork assistance that can help you get DMV appointments and fill out forms Skip Waiting On Hold
What’s more, you will find the option for both, silent and active monitoring, which means that if you want to provide training to a new colleague whilst another team member is in the midst of a support phone call, that is easy to do with the silent monitoring option. Or, if one of your team members is dealing with an issue that requires escalation and they need you to get involved that is possible too all in just a few clicks.