A man of eighty-two calls a service number one morning. His hearing is roughly where most people's is at that age: he can hear perfectly well that someone is speaking, and he loses every other consonant.
He hangs up after fifty seconds. In the log the call is recorded as abandoned by the caller, and there it stays.
The call below is constructed. None of the five moments in it are. They are the places where something has to have been decided in advance, and not one of them is solved by a better model.
How many people this covers
The Norwegian Institute of Public Health updated its figures in June. Around 19 percent of adults in Norway have some hearing loss when mild and one-sided losses are counted – roughly 800,000 people. About 6 percent have a moderate or greater loss, which usually means clear difficulty making out speech, especially with background noise.
The distribution is what matters for a phone number. Among those over 65, 59 percent have some hearing loss and 23 percent a moderate or greater one. Around 80 percent of all hearing loss in Norway is found in that age group.
If your callers skew over 65 – a municipality, a doctor's surgery, insurance, energy, property management – this is not an edge case. It is one of the largest single groups on the line.
Two filters in series
Age-related hearing loss starts at the top of the spectrum. The high frequencies weaken first, which is why the unvoiced consonants – p, k, t, s, f, h – are the first to disappear.
That is exactly the region the phone line has already thrown away. Ordinary telephony carries roughly 300 to 3,400 hertz, and the sibilants sit partly above that ceiling.
The two filters sit in series. The network takes the top of the signal, his hearing takes much of what is left. A caller of thirty barely notices the first one. He gets the sum of both.
And that is where the asymmetry lies that makes this a design question rather than an audio question: the agent can guess from context, look things up, ask for a repeat. He has only his ears.
The opening
The agent says who it is, who it answers for, and that it is artificial intelligence.
He catches "Hello, you're speaking with", and then a run of syllables.
The sentence isn't bad. The problem is that the two pieces of information that matter most sit in the part of the line where the pace is fastest and he is still working out what kind of call this is. The opening line is the only part of the setup every caller hears – provided it is built so that it can be made out.
What has to be decided: how fast the agent speaks, and whether there is a pause after the greeting. Half a second of silence costs nothing, and it moves the important part out of the busiest stretch of the line.
