Re: QT GUI Digital Number Control / inaccuracy

[Marcus D. Leech]

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.