CekuraBench
Book a demo

Cartesia Sonic 3.5vsAssemblyAI TTS 1

Cartesia Sonic 3.5AssemblyAI TTS 1
Compare

Speed and accuracy

Left is faster. Higher reads more hard parts right.

Fast and accurate60%70%80%90%100%00.5s1s1.5s2sTime until the caller hears the voice
  • Cartesia Sonic 3.5261 ms · 73.1%
  • AssemblyAI TTS 1171 ms · 81.5%

AssemblyAI TTS 1 is better on non-streaming latency, streaming latency, stopping, accuracy, naturalness and price.

Last updated Methodology by Dileep Chagam

Which is better at what

Measure by measure, the same sentences, the same place.

MeasureCartesia Sonic 3.5AssemblyAI TTS 1
  • Non-streaming latency (median)AssemblyAI TTS 1 is better261 ms171 ms
  • Streaming latency (median)AssemblyAI TTS 1 is better244 ms159 ms
  • Extra audio after a stopAssemblyAI TTS 1 is better809 ms40 ms
  • Hard parts read rightAssemblyAI TTS 1 is better73.1%81.5%
  • Naturalness (1 to 5)AssemblyAI TTS 1 is better4.414.50
  • Price per 1M charactersAssemblyAI TTS 1 is better$39.20$15.00
Hard parts read rightCartesia Sonic 3.5AssemblyAI TTS 1
  • Numbers and shorthand7 a.m. · 20% · 36°F · approx.69%74%
  • Codes and addressesSAVE20 · help@north-clinic.org · 1-800-555-019975%92%
  • Read from contextSt. Mary's on Main St. · Dr. Okafor54%71%
  • Medical termslevothyroxine · gastroenterology97%100%

An estimate: speech-to-text transcribers scored it, not people.

Hear both

The same sentence, read by each voice.

19 sentences, the same for both
  1. 01A greetingThanks for calling Cedar Valley Family Practice, this is Riley. How can I help you today?
  2. 02MoneyYour current balance is $1,347.09.
  3. 03A dateThe order was placed on 2026-03-14 and shipped two days later.
  4. 04Tracking codeThe tracking number is 1Z 7A4 X29 0341 8867.
  5. 05Email addressI have m.rivera88@example.org, is that still current?
  6. 06An Irish nameSiobhan Ó Briain called about the invoice.

How each ranks among all 27

MeasureCartesia Sonic 3.5AssemblyAI TTS 1
  • Non-streaming latency (median)9 of 274 of 27
  • Streaming latency (median)11 of 198 of 19
  • Extra audio after a stop7 of 73 of 7
  • Hard parts read right25 of 2714 of 27
  • Naturalness (1 to 5)15 of 274 of 27
  • Price per 1M characters17 of 262 of 26

Related comparisons

Cartesia Sonic 3.5 vs AssemblyAI TTS 1 FAQ

  • AssemblyAI TTS 1. Cartesia Sonic 3.5: 261 ms. AssemblyAI TTS 1: 171 ms.

  • AssemblyAI TTS 1. Cartesia Sonic 3.5: 244 ms. AssemblyAI TTS 1: 159 ms.

  • AssemblyAI TTS 1. Cartesia Sonic 3.5: 809 ms. AssemblyAI TTS 1: 40 ms.

  • AssemblyAI TTS 1. Cartesia Sonic 3.5: 73.1%. AssemblyAI TTS 1: 81.5%.

  • AssemblyAI TTS 1. Cartesia Sonic 3.5: $39.20. AssemblyAI TTS 1: $15.00.

Test your voice agent the same way.

Cekura runs these simulated calls on your agent and scores every one.

Book a demoStart free