What a low latency speech to speech voice agent is
A low latency speech to speech voice agent is software that holds a spoken conversation: it hears a person talk, works out a reply and speaks it back with very little delay. On a business phone line it answers the call, responds to questions and acts on them, with pauses short enough to feel like talking to a person.
The phrase packs in two ideas. Speech to speech means voice in and voice out, with no keypad menus and no typing. Under the bonnet that can be one model that works directly on sound, or a chain of steps (hearing the words, deciding the reply, speaking it) tuned to run fast. Callers can't tell which, and they don't care. They care about the second idea, low latency, which is the gap between them finishing a sentence and hearing an answer.
We don't publish a figure for that gap. A number measured in a lab says little about a call from a windy car park, and you can judge whether a conversation flows in a minute of listening.
Why an AI phone line says it is an AI at the start
An AI phone line says it is an AI at the start because callers have a right to know who they're talking to, and because the law increasingly expects it. Prepaid.ai opens every call with a short disclosure, on by default, worded for the country the business is in, before the business's own greeting.
The EU: tell people at the first interaction
Article 50 of the EU AI Act says providers must make sure AI systems that interact directly with people are built so those people know they're dealing with an AI, unless that's obvious to a reasonably well informed person. The information has to be clear and given at the latest at the first interaction (EU AI Act Service Desk, Article 50). The Act's general date of application is 2 August 2026 (Article 113).
A phone call is about the hardest place to argue that it's obvious. The caller can't see anything, and the voice is designed to be pleasant. Saying it in the first breath settles the question.
The United States: AI voices are artificial voices
On 8 February 2024 the Federal Communications Commission ruled that calls made with AI generated voices count as artificial under the Telephone Consumer Protection Act, effective immediately (FCC announcement). That ruling is aimed at calls placed to people, where consent rules apply, not at a customer ringing your business. It still tells you which way the wind is blowing.
The longer version, including what to put in your own greeting, is in AI phone disclosure rules.
What makes a voice agent feel natural
If it isn't pretending, what makes it pleasant to talk to? Mostly manners, and manners on the phone are about timing.
Quick turn taking
The hard part of a phone conversation isn't speaking. It's knowing when the other person has finished. People pause mid sentence, say um, and trail off while they look for a booking reference. An agent that jumps in at every pause is exhausting, and one that waits too long feels broken.
A good agent listens for the end of a thought, not just for silence. On Prepaid.ai the AI starts preparing its reply as soon as it's fairly confident you've finished, and commits once it's sure. That's what removes the dead air without trampling on a caller who's still thinking.
Letting the caller interrupt
Real callers interrupt. They say no, the other Tuesday, halfway through your sentence. An agent that ploughs on to the end of its paragraph feels like a recording.
Your AI stops and listens when a caller talks over it. There's one deliberate exception: the opening line. The disclosure and greeting are always said in full, because a caller who says hello the moment the line connects would otherwise cut off the sentence telling them it's an AI. How readily it gives way after that is a setting you can adjust.
Filtering the noise
Your callers aren't in studios. They're on building sites, in cars, in kitchens with the extractor fan going. Background noise causes two problems: words get misheard, and a slammed door gets treated as the caller starting to speak, which makes the AI stop mid sentence for no reason.
Noise suppression is applied to the caller's audio so the AI hears the voice and not the room. It's switched on for your line and you can turn it off if it ever gets in the way.
The small manners
A few smaller habits add up:
- Times are spoken as words, such as half past two on Thursday, the way a person would say them.
- When it doesn't know something, it says so and offers to take a message. It doesn't make up an answer to fill the silence.
- It says goodbye before it hangs up.
| What the caller notices | What's behind it | Yours to adjust |
|---|---|---|
| No awkward gap before the reply | End of turn detection that prepares early | How long it waits before replying |
| They can cut in | Interruption handling | On or off, and how sensitive |
| It hears them over the van engine | Noise suppression on the caller's audio | On or off |
| They know what they're talking to | Disclosure line, then your greeting | The greeting, not the disclosure |
Fast and honest are not in tension
Some businesses worry that announcing an AI will put callers off, and that the fix is a voice so smooth nobody notices. It's the wrong goal. A caller's real question isn't whether you're human. It's whether they'll get what they rang for. And a caller who works out halfway through that nobody told them feels tricked, which ends the call.
A quick, clear, honest agent answers that in the first ten seconds: yes, this is an AI, and yes, it can book you in, answer your question or put you through to a person. If you want to hear how a full call unfolds from the caller's side, read what a caller actually hears.
How to judge one with your own ears
Skip the spec sheet and run this test on any voice agent you're considering:
- Say hello before it finishes its first sentence. Does the disclosure still come through whole?
- Ask a question, then pause mid sentence for a breath. Does it wait?
- Interrupt an answer with a correction. Does it stop and take the correction on board?
- Call from somewhere noisy. Does it still catch names and days?
- Ask something it can't know. Does it admit that, or bluff?
Try it before you decide
You can run that test today. Prepaid.ai has a 7 day free trial with no card: paste your website, let the AI learn your business and talk to it in your browser. If you like what you hear, the plans are on the pricing page, and how to set up an AI phone walks through the rest.
FAQ
Does an AI phone agent have to say it is an AI?
In the EU, the AI Act expects people to be told when they're interacting with an AI unless it's obvious. Elsewhere rules vary, and saying it at the start of every call is the safest practice everywhere.
Will callers hang up when they hear it is an AI?
Some might. Callers who stay know what they're dealing with and tend to say what they need plainly.
What does low latency mean for a voice agent?
It means the pause between a caller finishing and the agent replying is short enough that the conversation feels normal. It's better judged by listening than by a quoted figure.
Can a caller interrupt the AI?
Yes. It stops and listens when the caller speaks over it, apart from the opening line that says it's an AI, which is always said in full.
Does the AI say it is an AI on every call?
Yes. The disclosure is on by default, comes first on every call and is worded for your country.
- ai-act-service-desk.ec.europa.eu/en/ai-act/article-50 · read 12 November 2026
- ai-act-service-desk.ec.europa.eu/en/ai-act/article-113 · read 12 November 2026
- docs.fcc.gov/public/attachments/DOC-400393A1.txt · read 12 November 2026
