Sonic Kinetic: An AI-Powered Workout Timer That Yells at You Using Gemini and ElevenLabs

I made an AI yell my workouts at me (Sonic Kinetic)

Marouane K built Sonic Kinetic, a workout timer that generates unique audio coaching for each routine. It uses Gemini to create interval scripts and ElevenLabs to produce real-time audio clips, with stability settings lowered to 0.30 for maximum-intensity segments.

Why This Matters

Most workout timers rely on static beeps or pre-recorded tracks, offering no personalization or adaptive intensity. Sonic Kinetic demonstrates a fully dynamic pipeline where AI generates both the workout structure and the audio coaching on the fly, with ElevenLabs’ stability knob tuned per segment to create a genuinely aggressive voice for high-effort intervals.

Key Insights

• Gemini 3.1 Flash Lite generates workout timelines with JSON schema enforcement, ensuring structured output without parsing errors (Marouane K, 2026).
• ElevenLabs’ eleven_flash_v2_5 stability setting is dropped to 0.30 for Maximum-intensity segments, creating a noticeably more aggressive voice (Marouane K, 2026).
• Go backend uses goroutines with sync.WaitGroup to parallelize ElevenLabs API calls, so a 12-segment routine doesn’t take 12x longer than a 1-segment one (Marouane K, 2026).
• Gemini 2.5 Flash was deprecated for new API keys, causing a 404 error during development (Marouane K, 2026).
• ElevenLabs free accounts cannot access stock library voices via API, resulting in 402 errors until a custom voice was used (Marouane K, 2026).

Practical Applications

• Fitness apps can use AI-generated audio coaching to create personalized, dynamic workout experiences without pre-recorded content.
• Audio generation pipelines can parallelize API calls using goroutines and sync.WaitGroup to avoid linear latency scaling with segment count.
• Pitfall: Relying on deprecated AI model versions (e.g., Gemini 2.5 Flash) can cause unexpected 404 errors; always check API deprecation status.
• Pitfall: Assuming free-tier API access includes all features (e.g., ElevenLabs library voices) can lead to 402 payment errors during development.

References:

• https://dev.to/marouaneks/i-made-an-ai-yell-my-workouts-at-me-sonic-kinetic-4ho2
• https://github.com/marwankous/sonic-kinetic