Dear Ferenc: Bruno Putseyz’s explanation in this thread says it all. EVERY ADC has an overload point, no matter how you slice it. EVERY ADC has to output in fixed point, because we’re talking about converting from the real (analog) world, which has defined analog voltages. You can CONVERT (or the device can convert) the output of the ADC to float, but it still had a defined overload point to begin with.
What Zoom has to be doing (there is no other way) is to move the 0 dBFS point to BELOW the overload point of the ADC. They can set it up so that a slightly higher analog voltage than is commonly used would cause the oveload. But that doesn’t make the ADC immune to overload, it just postpones the overload, at the expense of a worse signal to noise ratio. But as Bruno points out, the SNR of a good preamp and ADC is quite good, so it’s not a terrible thing to sacrifice a little SNR. But Zoom is misleading the customer and the article is entirely misleading. You don’t even need floating point to perform this “miracle”, actually. Just attenuate the input to the ADC inside the recording device.