[Discuss-gnuradio] Re: analysis_filterbank question

[feldmaus]

Eric Blossom <eb <at> comsec.com> writes:

> 
> On Mon, Jan 05, 2009 at 06:52:56PM +0200, Sebastiaan Heunis wrote:
> 
> Unlike what the code would lead you to believe, you have to provide
> the filter taps.  See gr-pager/src/usrp_flex_band.py for a working example.
> 
I found some API Docu about the analysis filterbank, but still
have some questions to it.

First i post a clipping from the api docu about the analysis filterbank:
00043     def __init__(self, mpoints, taps=None):
00044         """
00045         Takes M complex streams in, produces single complex stream out
00046         that runs at M times the input sample rate
00047 
00048         @param mpoints: number of freq bins/interpolation factor/subbands
00049         @param taps:    filter taps for subband filter
00050 
00051         The channel spacing is equal to the input sample rate.
00052         The total bandwidth and output sample rate are equal the input
00053         sample rate * nchannels.
00054 
00055         Output stream to frequency mapping:
00056         
00057           channel zero is at zero frequency.
00058 
00059           if mpoints is odd:
00060             
00061             Channels with increasing positive frequencies come from
00062             channels 1 through (N-1)/2.
00063 
00064             Channel (N+1)/2 is the maximum negative frequency, and
00065             frequency increases through N-1 which is one channel lower
00066             than the zero frequency.

What do you mean in line 61 + 62 ?
If i have 3 Mpoints, then my first channel comes from 1 to 0 ?
channel 2 comes from 1 to 0.5 ?
Channel 3 comes from 1 to 1 ?
If i have 3 mpoints than i have 3 channels, right ?

can somebody give a more detailed explanation ?

regards Markus