Why Does On Hold Music Usually Sound Terrible?

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No matter which kind of company you call — big or small — their on-hold music usually sounds like it has been recorded in a tin can. You would think that with modern technology being able to clone sheep and fly humans around faster than the speed of sound, that a creating a business phone system with clear and crisp on-hold music would be easy.  But as it turns out, it isn’t so straightforward.

Whether you are using an analogue landline or a VoIP business phone service, your voice travels over a variety of circuits and networks — most of which serve to disrupt the original audio 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.

Even if you have a VoIP telephone system, your call will eventually go across the PSTN (like the traditional landline calls), where network operators are able to do whatever they like. Plus VoIP and mobile operators use high-compression codecs that degrade the overall quality of the sound. A good codec can take a 9600bps audio stream (toll quality ISDN voice) and take it down to the required bandwidth by a factor of 10 or more.

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.

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.

So modern technology, even with the most advanced VoIP business phone systems, has not improved the plight of the on hold song. If you are interested in learning more, check out Tom Scott's explanation at the Milton Keynes Museum, in their Connected Earth gallery.


About VTSL

VTSL is the UK's best VoIP business phone system provider for medium sized enterprises.  VTSL offers a range of unified communidations solutions, connecting your organisations voice, email, CRM, mobile and conferencing for more efficient and productive working.  With easy-to-use phones and the most advanced cloud-based features, VTSL remains on the leading edge of telephony technology. For more information about VoIP business phone services, please call 020 7078 3200 or email


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