In a fascinating episode of “Things You Might Not Know“, host Tom Scott explains why telephone hold music sounds so awful compared to older times. In the past, the phone company would eliminate of high and low frequencies for speaking and then add them back in for music. This was an economical means to address long-distance calling in its infancy. The static that showed up later was due to the use of sound compression, computer use and advances in technology.
The standards for phone calls, even today, rely on quick-and-dirty compression built decades ago, designed to run on very little computing power, and optimised for speech. That compression is great at encoding one clear voice –but chuck a load of complicated music at it, with all its instrument and it’s going to sound bad. But not quite enough to break down into static. There is one last piece of the puzzle. Someone else cutting corners. Because in the worst case, that hold music isn’t just compressed by the phone company on its way to you. It’s already been compressed by a completely different system as your call bounces around a company’s internal phone network.