Re: Sample Rate and audio underflow ....

Look at your RTLSDR sample rate limitation

For example the RTL2832U can sample from two ranges ... 225001 to 300000 and 900001 to 3200000.

On 13/05/2021 22:30, Rob Roschewsk wrote:

Hi all!

I'm working on a "Hello, World!" flow in GRC .... just a simple NBFM receiver tuned to my local NOAA station.

Using an RTLSDR and the osmocom block ... into a low-pass that decimates by 5 into the NBFM block and then an audio sink. It doesn't get any more simple. Here is a image of the flow http://pabut.org/wiki/images/a/aa/My-fmrcv.grc.png

So with the sampling rate set to 2M .... works fine ..... if I REDUCE the sample rate, say 240k, I start to get audio sink underruns "aUaUaUaUaUaUaUaUaU" and I only get small blurbs of audio.

I'm sure to set the sample rate in the downstream blocks appropriately.

240k samples/sec should be plenty for a 5khz deviation FM signal ... right??

This is completely counterintuitive to what I was expecting.  I thought by reducing the sample rate I would lower CPU consumption ... and mitigate the exact problem I'm experiencing at the lower rate.

What am I not grocking here??

Thanks,

--> Rob