DSP-Newbie wrote:
> [email protected] wrote:
>
>>
>> Explicitly padding the input signal with zeros like this will work.
>> However, note that you're essentially delaying the input signal by
>> length(H) samples, so your output signal (even before you see any
>> transients) will also be delayed by length(H) samples.
>>
>
> I am aware of that, but its is not a problem; the delay is the same for
> all samples.
>
>
>
>>> My problem now was, which part of Y[] should I extract and use?
>>> After much and trial & error and some hair-pulling, I finally found a
>>> intuitive solution that actually works:
>>
>> -snipped-
>>
>> I forgot to ask before: why do you want to discard the transients? The
>> filter "startup" time is valid data, and occurs as your input signal
>> gradually fills up the delay lines that feed each filter tap.
>
> Perhaps I have not explained my problem clearly.
> I have set the soundcard to sample at 11.025 KHz, and to report the
> samples in blocks of 2048 samples, so I have to process about 5
> samples/sec.
>
> Each of these samples - after filtering, envelope detection, PLL bit
> sampler etc... - represents a number of bits, not necessarily a *whole*
> number of bits, which I have to cobble together block by block to
> reconstruct the original synchronous bitstream.
>
> Now, if I apply the algorithm as found in the book for each incoming
> datablock, I will have a startup transient for *each* block. There is no
> history from previous blocks. This results in repeating bit errors.

Then it is clearly the wrong algorithm. Look for overlap-add in the index.

> But, as I mentioned in my previous reply, the zero-padding etc. now made
> it working correctly.
> BTW: the filter performs **tremendously** well; I can now decode almost
> inaudible signals totally buried in the noise.
>
>
> [snip]
>> Remember, all you're trying to do here is implement the convolution
>> sum, nothing more.
>
> Sure, but I've had a hard time with it >:|

You probably ended up implementing one of the overlap methods.

Jerry
--
Engineering is the art of making what you want from things you can get.
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