I got this working. For completeness, I'll answer my own questions and sum
up what I've learned about filtering.
1) You need to call set_history(num_filter_taps) so that block boundaries
are handled smoothly
2) You input samples one at a time to fir_filter_xxf
3) fir_filter_xxf does not store data in it's own memory space, it uses the
address of the array element you give it to figure out the rest of the data
it should use to process around it, this is why history is necessary
The last problem I was having was related to converting an array of char to
float before feeding it into the filter. Not realizing how fir_filter_xxf
figured out what data to use, I was typecasting each char to float sample
by sample as the loop progressed and assigning the single float to a new
variable that was not an array. I then passed the address of this variable
to filter. This would cause the filter to use values in addresses around
that variable in its calculations, leading to ridiculous results. Don't do
this!
Rich
On Thu, Aug 20, 2015 at 12:37 PM, Richard Bell <richard.be...@gmail.com>
wrote:
> I have a fundamental misunderstanding of the filter system in gnuradio. I
> would appreciate some help. I wrote a simple C++ testbench to help me
> figure out what's going on, but it continues to not behave as I expect. I
> am using fir_filter_fff with 29 taps that I set. I send an impulse into the
> filter and want to see the filter taps at the output in response. The first
> sample that comes out is correct, but every sample after the first is
> either the smallest or largest number representable by float. The code that
> does this is below.
>
> float impulse[29] =
> {1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}; // 29 samples
> long
>
> float filter_taps[29] = {0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1,
> 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1}
> // input to filter
>
> shape_filter = new gr::filter::kernel::fir_filter_fff(1, filter_taps);
>
> for(int i = 0; i < 29; i++) {
> filter_out[i] = shape_filter->filter(&impulse[i]);
> }
>
> Printing filter_out to the screen produces:
> 0.1 0 8.12753e-44 1.61149e-43 -4.16205e-20 -8.32411e-20
> -1.24862e-19 -1.66482e-19 1.13358e+21
>
> When I expect to see
> 0.1 0.2 0.3 0.4 etc.., the taps of the filter that I set above
>
> You can see only the first output matches the expected.
>
> *What am I doing wrong here?*
>
> Thanks,
> Rich
>
> On Wed, Aug 19, 2015 at 12:02 PM, Richard Bell <richard.be...@gmail.com>
> wrote:
>
>> That fixed the problem. Thank you.
>>
>> Rich
>>
>> On Wed, Aug 19, 2015 at 11:56 AM, Tom Rondeau <t...@trondeau.com> wrote:
>>
>>> On Wed, Aug 19, 2015 at 2:17 PM, Richard Bell <richard.be...@gmail.com>
>>> wrote:
>>>
>>>> I'm having some trouble getting my code to compile. I get the following
>>>> error:
>>>>
>>>> error: ‘kernel’ does not name a type
>>>> kernel::fir_filter_ccf *d_shape_filter;
>>>>
>>>> To my *_impl.h file I added the following:
>>>> #include <gnuradio/filter/fir_filter.h>
>>>>
>>>> private:
>>>> kernel::fir_filter_ccf *d_shape_filter;
>>>>
>>>> To my CMakeLists.txt file I added FILTER to the dependency list:
>>>> set(GR_REQUIRED_COMPONENTS RUNTIME FILTER)
>>>>
>>>> I'm not sure where to go from here. What else needs to happen to call
>>>> kernel::fir_filter_ccf?
>>>>
>>>> Thanks,
>>>> Rich
>>>>
>>>
>>>
>>> Probably a namespace issue. You've included the fir_filter.h, I'm
>>> assuming. Now, instead of referencing it as "kernel::fir_filter_ccf" use
>>> the full namespace "gr::filter::kernel::fir_filter_ccf".
>>>
>>> Tom
>>>
>>>
>>>
>>>> On Wed, Aug 19, 2015 at 9:39 AM, Richard Bell <richard.be...@gmail.com>
>>>> wrote:
>>>>
>>>>> Thank you Jeff. Those are perfect.
>>>>>
>>>>> Rich
>>>>>
>>>>> On Tue, Aug 18, 2015 at 3:34 PM, Jeff Long <willco...@gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Rich,
>>>>>>
>>>>>> hilbert_fc.cc and filter_delay_fc both use kernel::fir_filter in a
>>>>>> relatively easy to understand way.
>>>>>>
>>>>>> Jeff
>>>>>>
>>>>>>
>>>>>> On 08/18/2015 04:26 PM, Richard Bell wrote:
>>>>>>
>>>>>>> Hi all,
>>>>>>>
>>>>>>> Would someone please recommend a good starting point in C++ source
>>>>>>> code
>>>>>>> that demonstrates how one uses the kernel::fir_filter. I started
>>>>>>> following the pfb_clock_sync method of implementing it, but then
>>>>>>> realized this had been customized a bit for the polyphase approach.
>>>>>>>
>>>>>>> I'm not doing anything fancy, I'm building a modulator and need to
>>>>>>> pass
>>>>>>> symbols through a shaping filter. The shaping filter is what I need
>>>>>>> the
>>>>>>> FIR filter for.
>>>>>>>
>>>>>>> Appreciated,
>>>>>>> Rich
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> Discuss-gnuradio mailing list
>>>>>>> Discuss-gnuradio@gnu.org
>>>>>>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> Discuss-gnuradio mailing list
>>>>>> Discuss-gnuradio@gnu.org
>>>>>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>>>>>
>>>>>
>>>>>
>>>>
>>>> _______________________________________________
>>>> Discuss-gnuradio mailing list
>>>> Discuss-gnuradio@gnu.org
>>>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>>>
>>>>
>>>
>>
>
_______________________________________________
Discuss-gnuradio mailing list
Discuss-gnuradio@gnu.org
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
