Note: if you have deleted the default music on hold and would like to restore it you may download the file from here. In the Upload audio file box, click Choose File to select a file from your computer, or type the location of the file.
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.

Website: https://www.spectrio.com/on-hold-messaging/how-to-craft-the-perfect-on-hold-message/#:~:text=How to Craft the Perfect On-Hold Message 1,5 Thank Your Customers for Their Time.
We provide bespoke on hold messages, more and more business is conducted over the phone all the time so it’s important you’re presented in the most professional and courteous manner possible. You should never consider putting a caller on hold as a bad move. This is your opportunity to continue informing your caller of important and interesting information about your business. 94% of marketing budgets are spent on attaining calls 88% of callers prefer on hold messages to any other option 70% of callers hang up after 30 seconds of silence 34% of callers who hang up due to silence will not call back 25% of callers stay longer due to on hold messaging 20% of businesses sales increased with on hold messages