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Re: [Discuss-gnuradio] QT GUI Range response (GNU radio companion)

From: Jan Simons
Subject: Re: [Discuss-gnuradio] QT GUI Range response (GNU radio companion)
Date: Tue, 16 Apr 2019 15:51:40 +0200
User-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

Hello Derek,
yes I use a low 8kHz sample frequency.
Use the ANAN200D with two phase synchronous receivers, analog line out (with AGC off) connected to an external sound card at 48kHz.
The audio is resampled to 8kHz and at the output back to 48kHz.

Only part of the processing needs to be performed at 8kHz.
By keeping the rest at 48kHz I was able to reduce the delays to normal values.
It is still not very fast, but for now it is ok.

Derek thank you for the help, it is much appreciated!

73 Jan PA0SIM

Op 16-4-2019 om 11:56 schreef Derek Kozel:
Hi Jan,

You've found the right place to ask. The IRC/Slack channel is also a good resource for talking to people.

Usually when delays are that long it's a sample rate issue. The underlying cause is that each block has some buffers so there's always a latency from input to output of sample period * total buffer length. At tens of megasamples per second that's not very much delay, but at lower rates, such as the audio rate you're probably using, that can be appreciable fractions of a second. You're describing multiple seconds which usually means there's a sample rate mismatch that's causing buffers to completely fill and back pressure the entire flowgraph. Do you notice the delay increasing over time?

That's about as far and specific as we can guess without seeing your flowgraph. Can you post your GRC file here for us to take a look at? That's the best although there's also a screenshot feature in the GRC menu. If you want to post a screenshot please host it somewhere else (like imgur) and link to it to keep the email size small.


On 4/16/2019 10:06 AM, Jan Simons wrote:
I just joined this group so hope my question fits this group.
I started with GNU radio companion a few month ago. Have been using Matlab/Simulink for about 15 years for DSP. Use it e.g. for ham radio shortwave noise cancelling and noise reduction.

I am using the widget QT GUI range in my models for changing settings.
What I have noticed is that a change in the setting is delayed by several seconds when the value is passed through an other block e.g. a multiplier or transcendental block . Even if I remove all not relevant processing.
So a change takes a few seconds to have an effect.

Have googled a lot but cannot find a hint.

Am I doing something wrong?
How can I improve the response time?


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