SynthID audio and MP3: does the mark survive Sume's 128 kbps detach?

Google DeepMind says SynthID audio watermarks are designed to survive adding noise, MP3 compression and changing the speed of a track (DeepMind, read 2026-10-02). Sume's audio detach can export a track as a 128 kbps MP3, so an MP3 export is not by itself a reason to expect the mark to vanish. Whether your track has a mark in the first place depends on the engine that made it.

What Google states about robustness

The page separates image and video claims from audio claims. These are design goals stated by the vendor, not guarantees, and the page gives no numeric figures.

Where Sume's MP3 comes in

Audio detach takes one Sume-hosted video and returns a new audio file: sample-exact WAV by default, or mp3 at 128 kbps. It is a worker ffmpeg step, billed per job at the public rate shown in the docs, and the source video is left untouched.

The step does not know about watermarks. If the source video carries a SynthID mark in its audio, the vendor's claim about MP3 applies to that transformation; if the source audio was made by a different engine, there is nothing for the claim to protect.

Checking what you have

• Keep the WAV as your master and treat the MP3 as a delivery copy.
• Ask which engine made the audio and keep that answer with the job id.
• Use Google's own detector tools for a check; the DeepMind page describes a SynthID Detector portal in early testing with a waitlist.
• Do not claim a file is watermarked because it came from Sume; Sume's docs make no such statement.

Honest limit

Google's page says detection covers its own tools, so a negative result says nothing about content from other vendors. This page reports the vendor's stated design and Sume's documented MP3 option, and it does not test either.