On 05/01/2021 10:37 AM, Tom Breyer wrote:
Dear team,
when I use "QT GUI Digital Number Control" to display a frequency I see
some "special effects".
Below 128MHz, it works fine but above I get wrong display data:
ok:
Input 128.001.000Hz -> Display = 128.001.000
not ok:
Input 138.001.000Hz -> Display = 138.000.992
Input 137.999.000Hz -> Display = 137.999.008
I simulate that input by using Gpredict via tcp port 4532 but found
debug messages ok.
Does that depend on the QT GUI Digital Number Control and the way it
converts numerical data types, since (128 = 2⁷)?
Can I adjust that module by my own?
73, Tom, DJ6TB
That's almost certainly an artifact of the machine representation of
single-precision floating-point
numbers.
I'm not that familiar with the message infrastructure and whether it can
carry double-precision values or not.
[The sample streams within Gnu Radio are almost always
single-precision floats, because;
A: Computations in single-precision are considerably faster than
double-precision
B: There's no numerical advantage to double-precision for most
signal-processing functions--there's more-than-adequate
dynamic range in a single-precision (32-bit) representation.
