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.
At Healthcare Messages On Hold, we specialize in delivering effective and informative custom telephone on hold messages to the healthcare industry. In any healthcare practice, on hold time is a fact of life. Patients’ calls often involve pulling a chart, looking into billing records or addressing questions that need attention from others.

Hold messages scripts are very powerful for you to keep your callers interested and reduce the tendency of drop calls. Here are some additional samples of hold messages scripts you can use for your business:
Whether you use the best hold music in the world or a simple repeating jingle, hold music is worth using for one reason. Customer retention. USA Business Telephone Today held a study of 30,000 callers.They placed each on hold for one minute, but split the callers into three groups and used different hold techniques on each before measuring the results.