Thoughts on FilteredStream/ConverterNChannel and FIR for SDRs

[thaaraak]

I am building a little SDR - the FIR filters are working out fantastic but one of the needs in an SDR is to:

1) Phase shift left and right channel by 90 degrees (this works fine) 2) Then either add or subtract left from/to right (this basically removes the unwanted sideband)

Point 2) needs to be in the API as typically you want to be able to programmatically switch between the two.

Now I have hacked ConverterNChannels to do the above

  size_t convert(uint8_t *src, size_t size) {
    int count = size / channels / sizeof(T);
    T *sample = (T *)src;

    T left,right;

    for (size_t j = 0; j < count; j++) {

        left = filters[0]->process(sample[j*2]);
        right = filters[1]->process(sample[j*2+1]);

        sample[j*2] = left + right;
        sample[j*2+1] = left - right;

    }
    return size;
  }

but obviously thats not the right way. Some thoughts I had: 1) Add a method to FilterStream to allow the caller to pass in an arbitrary Converter 2) Modify ConverterNChannels to support the above

I would prefer not to add the processing overhead of another chained FilterStream if possible

Thoughts?

ian

[pschatzmann]

I am currently providing the following functionality that provides multiple conversions:

• In the copier.copy() you can add a BaseConverter. You can also chain multiple converters with a MultiConverter
• Alternatively you can use a ConvertedStream instead (to which you pass a converter (including a MultiConverter) )

Did you manage to prototype your functionality in GNURadio ? I managed to have liquid-dsp compile in Arduino...

[thaaraak]

Heh - I saw you looking at liquid-dsp ;) I didn't get a chance to play around with gnu-radio.

Let me try your suggestions

[thaaraak]

I decided to go with adding a base converter to copier.copy() worked great