Analysis_filterbank


#1

Hi

I think I have found what might be my problem with the
analysis_filterbank. When using it as a polyphase channeliser, you
need to start feeding samples in from the bottom channel, upwards.
The gr.analysis_filterbank uses gr.stream_to_streams to split the
input into a number of streams starting at the top. For a polyphase
channeliser, this should be the other way round. I guess I need to
make a different version of stream_to_streams to do this. Can someone
please just help me with some c++ code? In particular the work()
function of gr_stream_to_streams:

const char *in = (const char *) input_items[0];
char **outv = (char **) &output_items[0];
int nstreams = output_items.size();

for (int i = 0; i < noutput_items; i++){
for (int j = 0; j < nstreams; j++){
memcpy(outv[j], in, item_size);
outv[j] += item_size;
in += item_size;
}
}

Firstly, why do we use a pointer to a pointer for the output data?
For what I intend to do, I need to do the following, right?

memcpy(outv[nstreams-j-1],in,item_size);
outv[nstreams-j-1] -= item_size; //or out[nstreams-j-1] +=
item_size?
in += item_size;

Thanks

Sebastiaan


#2

On Tue, Jan 13, 2009 at 08:45:43PM +0200, Sebastiaan H. wrote:

function of gr_stream_to_streams:
Sebastian, I think you’re confused about what’s going on.
Even if the output is backwards (I’m not convinced), you can just
rewire the output with connect. No reason to code a block.

}

Firstly, why do we use a pointer to a pointer for the output data?

Uhh, because it’s the correct type?

Look at the type of output_items. It’s

gr_vector_void_star &output_items

which is a typedef (gr_types.h) for

std::vector<void *>

There’s a distinct pointer for each output stream. The code writes N
output streams.

Eric

For what I intend to do, I need to do the following, right?