On Wed, Nov 17, 2010 at 2:45 PM, Marcus D. Leech <[email protected]> wrote:
> On 11/17/2010 12:43 PM, Marcus D. Leech wrote: > >> >> >> What I'm seeing is that the magnitudes (as seen in the number sink) coming >> off the source, even with roughly 75dB of gain ahead >> are roughly 0.002 to 0.003 when I'm using 400KHz sampling, and roughly >> 0.0006 to 0.0007 when the bandwidth is 250KHz. If you >> process the numbers as voltages, then we're talking a roughly 10dB drop >> in apparent average power level by reducing the bandwidth >> by less than 3dB. Both 400Khz and 250KHz use a decimation that is both >> even, and a multiple of 4, so they should be using exactly >> the same filter sequence in the decimator, correct? >> >> Marcus, you're a blithering idiot who should routinely be denied air. > You have clearly conflated the decimation/bandwidth numbers and > erroneously come to the conclusion that they should use the same half-band > filter lineup. They don't, you stupid, sorry excuse for > an advanced lifeform you. God, can you even tie your shoes reliably? > Let's see, 250KHz uses a decimation of 400, which uses both > half-bands in the FPGA because it's both even and a multiple of 4, whereas > 400KHz uses a decimation of 250, which is even, but not a > multiple of four, and so only uses a single half-band. So *naturally*, > the numbers won't "add up" between the two bandwidths. > > Frikkin' hell man, get a clue would you? Before I come over there and > whack you upside the head with a gnarly-great clue-by-four. > > :-) :-) :-) > > Don't be so hard on yourself...many of us would have still been stumped :) It's definitely not obvious/intuitive (to me, at least) that changing the decimation rate just slightly results in adding a whole 'nother additional set of filtering. Shouldn't the half-band filters have unity-gain in the pass-band? -Steven
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