Eloquence 64-bit for NVDA now supports a 44 kHz mode. It’s currently in preview and still being fine-tuned.
You can use the Sample Rate combo box in the Voices dialog to increase the default rate from 11 kHz to 44 kHz for clearer speech.
Unlike the 22 kHz mode in IBMTTS and ViaVoice, this mode doesn’t introduce pops, jitters, or unexpected voice resets.
Try the 16.1 upsampling preview release:
https://github.com/hozosch/eloquence_64/releases/tag/upsampling_preview
For more on the upsampling preview and author discussions check here:
https://github.com/fastfinge/eloquence_64/issues/88#issuecomment-4091293709
Release v16.1 upsampling preview · hozosch/eloquence_64

This version introduces the possibility to change the sample rate between 8, 11, and 44 KHz. 44 KHz is achieved by upsampling the 11 KHz signal externally via a CDLL. This is marked as preview unti...

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@amir I just tried installing this, and it broke my eloquence so bad that when NVDA restarted, it switched to the windows one core voices. when I try to switch back to eloquence, I get this error.

Synthesizer Error dialog Could not load the eloquence synthesizer.

@JamminJerry Try uninstalling your Eloquence add-on, restarting NVDA, and reinstalling the newer one.
@amir unfortunitly that didn't work either.