So what can we do to avoid inflicting further musical misery on our own customers while they’re patiently sitting on hold? We could just go back to playing a ringing sound, or an intermittent beep just to let people know they’re still connected, but that would be awfully dull. The best compromise is relatively simple electronic music that doesn't have too much going on as the ideal choice for hold music as it requires far less refined sound quality to get a decent rendition down a telephone connection.
Your call is answered and while being transferred to the relevant department you hear on hold messages. Whilst waiting their on hold message is informing you about the options available to you, from how your property will be advertised through to information about a free market appraisal on your property, followed by a great mortgage deal that is currently available.

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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