[hpsdr] Mercury sampling rate

[Alex, VE3NEA]

Hi Alberto,

The data blocks in the ring buffer do not need to be the same size as the 
input blocks, you can make them as small as you want. I have found that 
10-ms blocks work best.

Your fractional resampler approach is good. As always, there is a 
compromise - between the bandwidth sacrifice due to resampling, extra CPU 
load, and sound quality.

73 Alex VE3NEA




----- Original Message ----- 
>  Alex,
>
>    I agree of course on the numerical part of your analysis, but not on 
> the conclusions.
> Suppose that the output rate is 11025 Hz, a commonly used sampling rate 
> for output. If you do the processing in blocks
> of 1k samples, then each block correspond to a duration of about 92.9 ms. 
> If you receive CW at a speed of 30 wpm, the
> dot length is about 40 ms. So, when you have to throw away one block, 
> because you are in a condition of buffer overflow,
> you throw away more than two elements of the incoming CW signal. Not nice.
>
> The same for buffer starvation/underflow. In such a circumstance you have 
> to send to the sound card either a replica of
> the last buffer sent, or a buffer of silence. In both cases the effects 
> are very negative for CW. I agree that for SSB
> reception, especially in conditions of high QRM, maybe the fact can go 
> unnoticed, but not for CW.
>
> So I don't see alternatives to a continuously adjustable fractional 
> resampler, if what is sought is the best audio
> quality. But I would like to be wrong, as this choice as other negative 
> implications, which, if possible, I would like
> to avoid altogether.
>
> 73  Alberto  I2PHD 


 1208221055.0