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Re: [Discuss-gnuradio] dummy block has huge impact on usability fir filt

From: Martin Dvh
Subject: Re: [Discuss-gnuradio] dummy block has huge impact on usability fir filter
Date: Mon, 17 Jan 2005 19:38:09 +0100
User-agent: Mozilla Thunderbird 0.9 (X11/20041124)

Eric Blossom wrote:
On Mon, Jan 17, 2005 at 01:32:48AM +0100, Martin Dvh wrote:

Can you please update gnuradio-core (gnuradio-core/src/lib/runtime/gr_single_threaded_scheduler.cc is the
file that matters) and try your test with and without the dummy block?

I am compiling the new version right now. I will let you now the results as soon as possible.
extensive results at:

file used to generate results:

log of the session:

generated output files:

What I did was use my old driver which requires a high output_multiple.
I did an am_demodulation (like before) of a 5.0225 Mhz am modulated signal from 
a signal generator (modulation is a sinewave of I think 1 kHz)

If I use the dummy block the results are as follows.
Filter narrower as 2436.2 Hz gives a number of taps above 16015 and I have a 
silent output signal(like before).
Filter between 2436.2 and 4000 Hz does give output but is sounds strange. It is not a nice sine wave but sounds like the filter is resonating. If I stop the input it takes a while for the sound to fade away.
maybe this is normal for very narrow filters.
This behaviour I already get some time now but I think in the older cvs versions ( more then a month ago) the result was different. I am not sure about this. (I do have an older cvs version around so I may try to test this if I find the time)

with filters wider then 4000 Hz the output-signal starts to get normal.

If I do NOT use the dummy block I always get some output.
with trans_width wider then 4000 Hz the output starts to get normal.
below 4000 hz The sound is an intermittand sinewave.
It sounds like morse-code.
The narrower the filter, the longer the silence between the beeps.

If I use a transition width of 300 Hz the beeps are dozens of seconds apart.

you can listen to all output files.
I made a float filesink (audio_rate is 32127)
If you use it as a float filesource and connect it to dsp you can hear all 
the audio_rate, transition bandwidth and wether or not dummy_block is used is 
in the filename.

you can read the number_of_taps of every test in the log:


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