Imported Fish Audio voice ("Mana") — recent onset of garbled audio mid-call; previously stable

Support Help
1

Product area: Text-to-Speech (imported / custom voice)

Severity: High — renders affected calls unusable

Description

We use an imported Fish Audio voice named Mana on our Retell agents. This voice has worked reliably for us in the past — the instability is recent. Starting recently, calls using Mana intermittently produce corrupted audio: a sudden burst of “strange noise”/distortion in place of normal speech, after which the agent is unable to continue responding for the rest of the call. We saw this 3 times in a single test session on 2026-06-23 (PDT).

Because the same voice and configuration were stable previously, and the text the agent is attempting to speak looks normal in our logs, we believe something changed on the TTS synthesis/streaming side rather than in our setup or LLM output.

Voice details:

  • Name: Mana
  • Provider: Fish Audio (imported custom voice)
  • Voice ID: custom_voice_c9cd94fd5a53bca14cc385c189
  • Model: s2-pro
  • History: Previously stable in production/testing; degradation is recent

Affected calls (Retell call IDs):

  • call_34096c2022447d5928dde9e1459 — glitch at the end of the call
  • call_8b56c43167aed28f19131f2f726 — glitch from the start of the call
  • call_8078bee8c74332a6642c2a83a7a — glitch from the start of the call

Environment: Staging / test agents · Voice: Mana (Fish Audio, custom_voice_c9cd94fd5a53bca14cc385c189)

Impact: When this fires, the customer hears noise instead of speech and thee, so the call has to be abandoned.

Questions for Retell1. Can you inspect the recordings/synthesis logs for the call IDs above anddio corruption?2. Has anything changed recently on the Retell side for imported Fish Audiothat could explain a previously-stable voice degrading?3. We have two other imported Fish Audio voices we plan to test — Genki (cubb0582b6e) and Hoshi (custom_voice_6a0bac876b3d01ae58e92ebfd8). Would youexpect them to be affected by the same issue?
4. Is there a recommended mitigation (e.g., re-import the voice, different , retry behavior) to stabilize this for production?

2

@andrew3 Thanks forthe call ids, checking with the team.

3

Hey @andrew3 I’ve checked with the team, and Fish Audio has been experiencing issues over the past couple of weeks. Please try using a different provider for now.

Thank You

4

Hi, following up on this thread with a new incident and questions.

Outage window: July 6, approximately 11:26 AM – 12:00 PM JST (02:26 – 03:00 UTC). The issue resolved on its own around 12:00 JST.

Symptom: During this window, all of our agents using imported Fish Audio voices (all s2-pro model) stopped speaking with their configured voice:

  • Genki v2 — custom_voice_92fbb64807fa5ee31ec4f84c75
  • Hoshi — custom_voice_6a0bac876b3d01ae58e92ebfd8
  • Mana — custom_voice_c9cd94fd5a53bca14cc385c189

Instead, every one of them produced the same substitute voice with a strong English accent and badly degraded Japanese — it could not read kanji or numbers at all, and in one call it repeated the same phrase over and over. Switching an agent from Genki v2 to Hoshi mid-incident made no difference; the same English-accented voice came out. Voices from other providers (Cartesia) were unaffected, which is how we mitigated.

Example call IDs from the window:

  • call_a8ca3c258ed469cbc215bda3cb8
  • call_497cbb25e6a6f0667807ce856f1
  • call_6c453bcdf9a2cc6cc749dc9d2c0 (repeated-phrase behavior)
  • call_71bf0b607ee75936fb8985f2f8b
  • call_8ac8f789fd85e959b3a142aff45

The fact that three differently-configured voices all collapsed to one identical voice looks like a fallback to a default voice/model rather than ordinary audio corruption. So my questions:

  1. Where does this fallback happen — on Retell’s side or on Fish Audio’s side? I.e., when Fish Audio has issues, does Retell substitute a fallback TTS voice, or does Fish Audio itself serve a default voice when the requested custom voice is unavailable?
  2. Is there any way for us to control or configure the fallback voice? Our agents serve Japanese-speaking callers, so falling back to an English-accented voice that can’t read kanji is effectively a full outage for us. If we could designate a fallback (e.g., a Cartesia voice we know works for Japanese), a Fish Audio incident would degrade gracefully instead.
  3. Was there a known Fish Audio (or Retell TTS-layer) incident during that window? Any detail on the trigger would be appreciated.

Thanks!

5

Hey @andrew3 Thank you for providing the details. I’ve shared them with our team for review.

We’ll get back to you as soon as we have an update.

6

Hey @andrew3 Retell does have a fallback mechanism to switch to another voice if the primary voice encounters an error.

Yes, you can select the fallback voice in the settings (Security & Fallback Settings).

We did not receive any reports of an incident during this time.

Thank you

7

Thanks.

Do your logs show evidence of fallback being triggered in our test calls? Is there a way that I can see if the fallback voice is triggered?

Andrew

8

Also, what is the default fallback voice that Retell uses if we don’t set our own fallback? How does this behavior work?

Thanks,
Andrew

9

Hey @andrew3 Yes , there was an error and we tired a fallback.

image

10

@andrew3 Retell will try to match to a close voice to the one you have , and you can also configure the fallback voice yourself from the fallback settings.

Thank You