So I also found the related patent by Texas Instruments
here
It seem to be a very detailed explaination of dynamic range enhancer. And it's not a new idea as several earlier patents also explored this direction. The motivation is far-field voice pickup, and not to let signal-to-noise ratio (SNR) limit the dynamic range. With a customer-level audio knowledge I could not get how it worked from just a glance.
At least we have the measurements in
TLV32ADC5140's manual and here it is:
Notice how noise floor is 12 db lower than when DRE is disabled, and the signal stays at -60db (that might have something to do with the later digital filter part about scale factors, explained in the patent)
If we just consider very low level recording then sure it's 12db of free dynamic range. But signal-to-noise ratio is not changed at all so the use case seems to be very limited. Like
@Cbdb2 explained that it works like an expander to expand the DNR.
Look at the explaination
provided by AP about why dynamic range is measured using 0 dbFS signal vs. -60 dbFS noise floor:
· In both ADCs and DACs, “idle tones” can be produced within the converter in the absence of applied signal. In the method here, a low-level tone is applied to the converter to avoid production of idle channel noise. The low-level tone is removed by a notch filter before measurement.
· In some DACs, the output of the device is switched off when there is no signal, providing an unrealistically quiet measurement. The low-level tone (again, notched out before measurement) defeats this muting mechanism.
To me DRE looks like a fancy "switch off" mode, although technically we can still use the device for "far field pick-up" but for most recording scenarios there's a 12 db differences between SNR and DNR, which can sometimes confuse customers. Looks it's more of a designed overfitting technique to optimize the score based on AES17 dynamic range measurement standard. It is now also widely used as a marketing tool by manufacturers and people are just crazy about the excellent "123dbA dynamic range" without knowing whether that in most cases that cannot bring more headroom in their recording work.
By the way
@MC_RME I appreciate RME for providing only the SNR number and they are not just number on spec but also what people can get in real use cases. Not good for marketing though.