Re: Sample Rate & Hardware Considerations Tutorial: GNURadio.org

[Barry Duggan]

James,

1) Yes, the spec sheets are the answer. For the FunCube Pro+, the only 
rate is 192kHz.

2) I REALLY need to revise that section! The use of the term 
'multiplier' is misleading. The Rational Resampler is Interpolating and 
Decimating to create the output sample rate. However, if you look at the 
Properties for it, those values are not underlined, signifying that you 
can not change them at run-time. Therefore your slider didn't work.

My approach to picking sample rates would be to look at both ends of the 
data flow to determine what sample rates are required. For example, if 
the output is an Audio Sink, you have a maximum of 48kHz (usually). For 
Wide Band FM you need at least 96kHz, and more is better. As long as you 
get to set an input sample rate, as most devices allow, then the optimal 
choice is to pick an integer multiple of the 96kHz. Then you can have an 
integer value of decimation.

Enjoy GNU Radio!
---
Barry Duggan KV4FV

On 5/1/20 2:09 PM, James Hayek wrote:
> Well, thank you for creating the documentation! I really look forward to 
> learning as much as I can comprehend, and pushing my limitations of 
> understanding. Thanks for you and the teams' hard work.
>
> Interesting point on Question-01. Yes, you are correct… 200 kHz 
> bandwidth. I guess I was considering the guard bands (25 kHz upper and 
> lower). Thank you for clarifying. I verified here:
>
> http://hyperphysics.phy-astr.gsu.edu/hbase/Audio/radio.html
>
> I wondered why you used 192k for the FunCube.
>
> Follow up question:
>
> ·How can I know the max sample rate for each device?
>
> oAssumingly, reading the Spec Sheets? (Until I’m clever enough to build 
> my own!)
>
> For Question-02, I was referring to: 
> https://wiki.gnuradio.org/index.php/Guided_Tutorial_Hardware_Considerations, 
> apologies for not being explicit.
>
> Here, the author used a multiplier of 1.05
>
> I.e., for the Rational Resampler Block used:
>
> ·*Interpolation:* int(1.05 * (audio_rate * audio_interp))
>
> ·*Decimation:* int(samp_rate)
>
> I mapped that value of 1.05 to a slider and adjusted it during playback. 
> It made no difference. I assumed this is because it did not have enough 
> weight to push the sample rate in or out of range. After doing the 
> actual math, I see the multiplier I used will never bring the value to 
> the sample rate I needed for my particular device.
>
> To verify, I created a follow up slider where I adjust the sample rate 
> value. It shows me pretty clearly where the limit lies. Below is the new 
> flow graph.
>
> image.png
>
>   For the reference to your name, I was following the Sample Rate 
> Tutorial you wrote. I must of assumed you also did the follow up lesson 
> stated above. Your name was attached to:
>
> https://wiki.gnuradio.org/index.php/Sample_Rate_Tutorial
>
> Sorry for the confusion, but thank you for the help!
>
>
> Many thanks,
>
>
> On Fri, May 1, 2020 at 1:24 PM Barry Duggan <address@hidden 
> <mailto:address@hidden>> wrote:
>
>     James,
>
>     Thank you for your comments on our documentation! I started working on
>     the docs last year including adding flowgraphs to the block docs and
>     updating the tutorials to rel 3.8. The
>     https://wiki.gnuradio.org/index.php/Guided_Tutorial_Hardware_Considerations
>
>     is one which has been updated recently, but I didn't have the hardware
>     to test it. (I will next week).
>
>     So, for question 1: that tutorial was written several years ago. I
>     don't
>     know why that sample rate was chosen, but some older computers have
>     trouble with high sample rates. Actually the broadcast FM signal in the
>     US is 200kHz with all the SCA, etc. but the minimum for stereo is less.
>     If you look at the flowgraph for
>     https://wiki.gnuradio.org/index.php/WBFM_Receive I use 192kHz because
>     that is the rate for a FunCube Pro+.
>
>     For question 2: In the tutorial
>     
> https://wiki.gnuradio.org/index.php/Guided_Tutorial_Hardware_Considerations#A_Working_Software_Radio_Broadcast_FM_Receiver
>
>     there is no multiplier, so I am guessing that you are looking at
>     https://wiki.gnuradio.org/index.php/WBFM_Receive where the multiply
>     block is the volume control.
>
>     You said "In your (Barry Duggan's) example the multiplier helped to
>     remove his static". Can you tell me which of my examples you are
>     referring to?
>
>     Best regards,
>     -- 
>     Barry Duggan KV4FV
>
>
>
> --
> Thanks,
> James G Hayek
> Youtube.com/JamesHayek