squarewave

Re: 32 bit float
« Reply #20 on: January 11, 2020, 11:37:23 AM »
Lets assume that you have  24 bit converter with a maximum input (analog level) of +22dBu, thats 9.76VRMS or a peak voltage of 13.798V, That means that the lowest step (the LSB) the converter can code is 13.798/(2^24) = 0.82 microvolts, thats -122.5dBU (after converting to RMS) of minimimum signal, thats the noise of a 1Kohm resistor across a 20KHz bandwidth, giving a roughly 144.5 dB of dynamic range, most microphones or line level devices are no way near that noise floor, which basically means that the first 3 or 4 bits in your 24 bit converter are always on, effectively making your 24bit converter into a 20 bit or so converter. So whats the point of having a 32bit converter? I do agree that 32 bit float in post processing provides an advantage, but in the conversion stage?  I dont think so, to me 20bit is more than enough.
I didn't intently study your numbers but I assume you're considering that the converter IC is not taking +22dBu. It can only handle ~4Vpp which is more like +5dBu. That means the input is being attenuated by ~17dB (something an integrated pre would not bother to do incidentally). So that -122.5dBU is more like -139 and the theoretical limit of a 24 bit converter is a little more than 140 so that all seems to match up.


 

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