Article: Understanding Digital Audio Measurements

[guigui]

SINAD in these devices is usually dominated by noise. There, there can be small differences due to ground current/loops, that account for some of that difference. Other differences could be real but is really not material. FYI in my SINAD ranking graph, I use the average of the two channels.

Thanks a lot, Amir!

 

[danhilu]

Hi Daniel. I see that my explanation was perhaps not as clear as it could be. But I got lost half-way through yours as it got too long!

Fair enough.
Short version: the statement "So if I set the digital generator to -120 dBFS, it means I am telling the DAC to reproduce a voltage that is represented by 120/6 = 20 bits." is wrong.
-120 dBFS corresponds to a signal where 20 bits are unset - using @danadam 's phrasing. The voltage is "represented" by at most 4 bits - using your phrasing @amirm.
120 dB "corresponds" indeed to 20 bits, but you have to remove these from the available 24 bits. As I've laboriously tried to explain above

 

[danhilu]

@danhilu Well, this also wrong; because if you want to be accurate, at 16 bits the dynamic range is ~90dB and ~138dB at 24 bits (if we do not dither). This is because audio samples are signed number. Which implies another inaccuracy in your post above: the most significant bit is always “used”.

Thank you @melowman. Excellent. Signal also need to get negative. You're right of course.

 

[danhilu]

I think you are confusing bits needed with bits set/unset. With lower amplitudes the top bits are unset (ignoring two's complement for now) but they are still needed.

Thank you @danadam . I am not convinced by my wording either. I was trying to transform an input statement which I have understood is not correct into something a layman with some motivation could decipher. I think you're right, "unset" is better than "needed". Bottom line is my reply to @amirm above: I think there is an error in the initial text.

 

[LionIT]

What is the type of window that AP applies to make FFT of various measurements? Rectangular? Blackman Harris?
I noticed in REW that the window type changes the results enormously sometimes, especially at very low levels.