On 9/14/2010 9:44 AM, Invisible wrote:
>>>> Take a signal, repeatedly break it up into pairs of low and high
>>>> frequencies, subsample those segments, and place them back into the
>>>> buffer.
>>>
>>> I'm not at all clear on exactly how it does that.
>>
>> Using a pair of filters, low pass and high pass in a bank,
>
> Doesn't look like any kind of lowpass or highpass filter response to me.
> Looks more like it's rearranging the order of the samples or something.
>

What it appears to be doing is for every 2 samples:

The first of the pair gets the same positive value on its respective 
sample in the first and second half. The second of the pair is then 
added to the sample on the first half, and subtracted from the sample on 
the second half.

Subsample and repeat the desired number of times.

> When downsampling, frequencies above the Nyquist limit get reflected to
> the other side of the Nyquist limit. Usually this means that the high
> frequencies collide with the low frequencies - but if you've already
> filtered out the low frequencies, all that happens is that the spectrum
> gets flipped upside-down. You can completely reverse this process by
> upsampling and then flipping the spectrum back the right way round
> again. QED.

OK, Makes sense.


> Weird, but true. And since quantum particles ARE ALSO WAVES, you start
> to understand why this might be true...

Right.

-- 
~Mike

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