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A persona defines who the simulated user is and how they sound — their voice, accent, personality, and speaking style. A persona pairs with a test case, which defines what the user is trying to do. Keep behavioral traits in the persona and task instructions in the test case — don’t mix the two. A persona has two parts: A few additional technical settings cover multilingual recognition, hold-music disconnects, and phone-number routing.

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Creating a persona

  1. Navigate to the Personas section.
  2. Click Create New Persona.
  3. Give the persona a Label (its display name) and, optionally, customize the Avatar — select hair, eye, and lip styles, or regenerate the seed for a new base face.
  4. Configure the settings below and save.
Persona configuration — identity settings

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Who they are

A persona’s personality and behavior come from two places: the Persona Characteristics prompt and a few behavioral settings. The Persona Characteristics prompt (required) describes the persona’s demographics, personality, and communication style. The language model generates the persona’s dialogue from this prompt, and the text-to-speech engine speaks that text — so emotion, hesitation, and pacing all come from the words you tell the persona to use, not from vocal controls. Use the expand button (Shift+E) for a full-screen editor.

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Emotional tone

Describe emotional behavior in terms of word choice and conversational patterns, not generic labels:
Punctuation acts as a speech cue for the TTS engine: Real callers escalate or de-escalate, so include emotional progression:
Higher-realism voices generally produce better emotional expressiveness — but they have a ~12 connection concurrency limit, so use higher-concurrency voices for high-volume runs where expressiveness matters less.

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Filler words

TTS engines process text literally — unusual spellings or repeated letters can cause them to spell out letters or mispronounce sequences. Use standard spellings: Include explicit TTS-friendly instructions in the prompt:

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Conversation triggers

To make the persona stay silent until the agent says a specific phrase (e.g. waiting for a greeting):
  1. Set the Conversation Initiator to “Persona waits to speak” so the agent always speaks first.
  2. Use strong, repeated language in the prompt:
  1. Keep the trigger phrase simple and distinctive — shorter, common phrases are easier to detect reliably.
  2. Include fallback behavior so the conversation doesn’t stall:
Because the underlying model is probabilistic, trigger adherence is high but not perfectly deterministic. For mission-critical trigger behavior, run multiple simulations to account for natural variation.

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DTMF/IVR and call endings

In a voice persona prompt you can also specify navigation and call-control behavior — DTMF/IVR menu handling, speech style, when to provide or withhold information, and when to hang up.

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Behavioral settings

Alongside the prompt, a few structured settings shape how the persona paces and times its speech during voice simulations.

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Interruption and turn-taking

Voice simulations involve two distinct types of overlap:
  • Proactive interruptions — controlled by the Interruption Rate setting (None / Low / Medium / High). When set to None, the persona never deliberately talks over the agent.
  • Natural turn-taking overlap — even at None, the persona may start speaking while the agent is still talking, because the speech-to-text engine interprets a brief pause as end-of-turn. This mirrors how real callers sometimes talk over agents.
To make the persona more patient and reduce overlap, add explicit waiting instructions and slower speech patterns to the prompt:

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How they sound

Configure the persona’s voice and audio environment.
Persona voice, language and accent, and background noise settings
Voices fall into two categories based on realism and concurrency. Higher-realism voices sound more natural and expressive but support only ~12 simultaneous connections — for high-volume runs, use higher-concurrency voices to avoid bottlenecks.Higher Concurrency (34 voices)Higher Realism (37 voices) — Limited Concurrency
Concurrency limit: Higher-realism voices support a maximum of ~12 simultaneous connections. For high-volume runs, use higher-concurrency voices to avoid bottlenecks.

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Custom background sounds

Beyond the built-in library, you can upload your own background sound — for example, a recording of your own call center floor, your hold music, or a specific noise profile you want to test against. Uploaded sounds are private to your organization and appear in the same picker alongside the built-in options. Each uploaded sound has an acoustic source type:
  • Ambient (ambient): mixed as diffuse background noise. For soundscapes like a cafe, park or rain.
  • Point source (point_source): treated as a localized sound source. For individual sounds like another speaker, a doorbell or baby crying.
Point-source sounds are spatially rendered only when the persona has a Situate Speaker preset enabled. Without a situate-speaker preset, point-source sounds are mixed like ambient sounds.
1

Upload a sound

In the persona’s background-sound picker, choose to upload a file. Give it a name, select a .wav or .mp3 file, and choose an acoustic source type.
2

Select it on the persona

Once the upload completes, the sound appears in the picker. Select it like any built-in sound and set the volume with the slider.
3

Run a simulation

During voice simulations, the sound is mixed into the persona’s side of the conversation and loops for the duration of the call.
Pick a sound that loops cleanly if you expect long calls — the file repeats for the length of the conversation, so an abrupt cut or trailing silence will be noticeable.

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Advanced

The persona configuration modal’s Advanced panel covers multilingual recognition, hold-music disconnects, custom text configuration, and agent-voice routing.
Advanced persona settings — multi-language STT, hold music timeout, text configuration, and agent voice

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Multi-Language STT

Found under Advanced in the persona configuration modal. Enables multilingual speech recognition so the persona can accurately hear and respond to agents that speak multiple languages in the same conversation (e.g. “For English press one, Para español presione dos”).
To test the same agent with and without multilingual recognition, clone a persona and toggle this on the copy.

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Hold Music Timeout

Found under Advanced in the persona configuration modal. Disconnects the persona after a period of silence or hold music, instead of waiting for the default timeout. Useful for testing live-agent transfer flows — set it to 10–15 seconds to confirm the transfer happened without sitting through extended hold music.

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Version history

Every config-changing save of a persona — its prompt, voice, language, or behavioral settings — is recorded in its version history, so you can see how the persona changed over time and tell which version a run used. See Versioning for how copy-on-save works and how to pull the history through the v1 API.

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Caller phone number

Coval uses different phone numbers depending on the simulation type. Assign a specific phone number index to a persona if your workflow depends on phone-number routing.