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.
VoIP providers also use other audio technologies such as silence suppression, background noise removal, echo cancellation, etc, which also affect the way voice sounds, and on hold music too.

Besides that, its a music player that goes full screen on landscape mode and has a funny sound board. I made a toggle button that hangs so you can use it for hold music during a call. Thus whenver someone puts you on hold just hit the hovering musical note and start playing music. Or play music while someones on the phone with you.
If your phone system(s) or VOiP solution has a built-in MOH player, we can format and deliver your audio file to provide optimum performance. If you are using Cisco, Avaya, NEC, Samsung, or virtually any available system, we’ll determine and deliver exactly what you require.