Does the watermark work at 8 kHz?
Aureal accepts audio from 8 kHz, but the standard 4.5–13.5 kHz and 17–19.5 kHz carriers cannot exist under an 8 kHz Nyquist limit. The embedder therefore uses a single fallback band inside the available spectrum (roughly 2.1–3.9 kHz), a weak speech-band host. A 44.1 kHz marked file downsampled to 8 kHz loses both standard carriers; do not expect recovery from that path.
How Aureal handles it
At an 8 kHz sample rate the usable spectrum ends at 4 kHz. The standard mid and high presets start at 4.5 kHz and 17 kHz, so neither fits; the embedder chooses one wide band under Nyquist instead, which places the mark in the speech region where codecs and noise do the most damage. The same limit applies in reverse: if you mark a 44.1 kHz master and then downsample it for a telephone or voice-assistant path, the resampler removes both standard carriers before the file reaches the far end. Upsampling the 8 kHz file later cannot restore the removed band.
Common failure mode
“Downsample the marked promo to 8 kHz for the phone and the ID will still trace the call.”
Why it fails: A true 8 kHz downsample discards everything above 4 kHz, which includes both standard carrier bands. Only a file embedded after the 8 kHz conversion uses the fallback band, and even that path is a documented weak case once a telephony codec and network noise are applied.
Verified example
Compare the two paths instead of assuming they are equivalent:
ffmpeg -i marked-44k.wav -ar 8000 -ac 1 downsampled.wav
node aureal-watermark.cjs detect downsampled.wav --id 883921
ffmpeg -i master.wav -ar 8000 -ac 1 master-8k.wav
node aureal-watermark.cjs embed master-8k.wav marked-8k.wav --id 883921
node aureal-watermark.cjs detect marked-8k.wav --id 883921
Then test the actual telephony codec; a pass on the WAV is not a pass on the call.Example only. Validate against your own audio, codec and processing chain.
Scope and limits
- Standard mid and high carriers do not fit at 8 kHz.
- Only the fallback band (roughly 2.1–3.9 kHz) is available at 8 kHz.
- Downsampling a 44.1 kHz marked file destroys both standard carriers.
- 8 kHz is a documented weak case; telephony codecs make it weaker.
Frequently asked questions
Will a phone recording decode?
Only if the mark was embedded at 8 kHz with the fallback band and survived the telephony codec and noise. That is a weak, test-every-time path, not a guarantee. A downsampled 44.1 kHz mark should be treated as gone.
Can I upsample the 8 kHz file back to 44.1 kHz?
You can, but resampling cannot recreate energy that was removed. The standard carriers are still absent; the file remains an 8 kHz-bandwidth recording for watermark purposes.
Related topics
Test the actual delivery chain. A fixture result is a starting point, not a guarantee for your material.
Open the Studio →