Re: [Discuss-gnuradio] isolate channels from wideband

[Chris Kuethe]

I have produced a complementary demonstration of the polyphase channel
synthesizer and a tool for generating test signal. As before, it was
developed using the a very recent gnuradio release (3.7.8rc1) so older
installations may be unable to load the grc file. Will publish
shortly...

As a meta point, I encourage everyone developing with gnuradio to
build test tools and synthetic data sources before starting on the DSP
work (or make some good recordings if you're working with real world
signals). As I am not blessed with 5 or 6 audible NOAA stations, I
wrote a tool to generate distinctive audio streams that could then be
fed through the synthesizer - in this case "flite" was used to convert
the weather reports for 7 different airports to wav files, and a
prologue containing expected channel number and frequency offset was
prepended. This allowed me to very easily hear when/if the channelizer
was correctly selecting the channels I wanted.

On Thu, Aug 6, 2015 at 7:08 AM, Daniele Nicolodi <address@hidden> wrote:
> On 22/07/15 15:40, Tom Rondeau wrote:
>> On Wed, Jul 22, 2015 at 4:57 AM, Daniele Nicolodi <address@hidden
>> <mailto:address@hidden>> wrote:
>>
>>     On 21/07/15 21:39, Tom Rondeau wrote:
>>     > Here's my presentation from last GRCon:
>>     >
>>     > http://gnuradio.squarespace.com/grcon14-presentations#tut-rondeau
>>
>>     Hello Tom,
>>
>>     browsing through your presentation I see that on page 58 and 59 you
>>     recommend to use firdes filter design tool and not optfir to build re
>>     reconstruction filter.  However, I don't quite understand why the filter
>>     generated by one tool is better than the other is this case.
>>
>>     Can you please comment on it?
>>
>>     Thanks! Cheers,
>>     Daniele
>>
>>
>> The shape of this filter matters greatly. The inband, transition, and
>> stop band behavior all determine if the filter can be used for the
>> reconstruction purposes. The image on slide 59 shows the specific
>> transition between the pass band and stop bands. To match that with the
>> PM (i.e., Remez) algorithm, you can't get the same stop band performance
>> for that given transition. Plus the equal response in the stop band is
>> bad when channelizing because all channels will alias at equal powers,
>> whereas the roll off in frequency with the windowed (firdes) filter
>> continues to decrease with f. Remez also produces a pass band ripple,
>> which will also affect things. The ripple with the firdes is not
>> equiripple like Remez promises, but it's much, much smaller.
>
>
> Thanks Tom, very clear explanation.
>
> Cheers,
> Daniele
>
>
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GDB has a 'break' feature; why doesn't it have 'fix' too?