# 27jun08

 # setup A/D rms Relative noise power vs fftlen 8192 1fff 4096 fff 2048 7ff 1024 3ff 512 1ff 256 ff 8k 4k 2k 1k .5k 1 jun08 standard 9 shifts then 0,1... 30 1/2 1 1/2 1 1/2 0x1ff5 1 1111 1111 0101 shifts=11 0xffa 1111 1111 1010 shifts=10 0x7fd 111 1111 1101 shifts=10 0x3fe 11 1111 1110 shifts=9 0x1ff shifts=9 0xff shifts=8 2 9 shifts then 0,1 15 1/8 1/4 1/8 1/4 1/8 .. .. .. .. .. .. 3 10 shifts then 0,1,0,1 30 1/2 1/4 1/2 1/4 1/2 0x1ffa 1 1111 1111 1010 shifts=11 0xffd 1111 1111 1101 shifts=11 0x7fe 111 1111 1110 shifts=10 0x3ff 11 1111 1111 shifts=10 0x1ff shifts=9 0xff shifts=8 4 butterfly 1, no shift then 9 shifts, then 0,1 15 1/2 1 1/2 1/4 2 0x0ffa 0 1111 1111 1010 shifts=10 0x7fd 0111 1111 1101 shifts=9 0x3fe 011 1111 1110 shifts=9 0x1ff 01 1111 1111 shifts=9 0x0ff 0 1111 1111 shifts=8 0x7f 0111 1111 shifts=7 5 butterfly 1, no shift then 10 shifts then 0,1 15 1/8 1/4 1/8 1/4 1/2 0x0ffd 0 1111 1111 1101 shifts=11 0x7fe 0111 1111 1110 shifts=10 0x3ff 011 1111 1111 shifts=10 0x1ff 01 1111 1111 shifts=9 0xff 0 1111 1111 shifts=8 0x7f 0111 1111 shifts=7

• 1: jun08 standard: using a/d rms=30
• 12 bits in upper 18 bits gives 6 shifts for free.
• 6 stages, noise grows by 3 bits
• so do 9 shifts then every other shift..
• 2: 10 shifts then 0,1
• Power for odd len fft :8192,2048, ... the same
• Power for even len fft: 4096,1024,...
•  first butterfly stage is no shift.. then 9 shifts.
• Then alternate 0,1,0
• Shifts make size increase by sqrt 2. rms make value decrease by 2.

 date mode 8k 4k 2k 1k .5k 02jul08(285,10) 1 rms=30 no pfb ovdrflows, 0x1ff5 pfb overflow, 0xffa 02jul08 2 rms=15 no pfb overflows, 0x1ff5 pfb overflow, 0xffa 02jul08 4 rms=15 pfb overflow, 0x7fd 02jul08 rms=30 03jul08(285,10) 1 rms=30 no pfb overflow, 0x1ff5 no pfb overflow, 0xffa pfb&adc overflows,0x3fe 03jul08 2 rms=15 no pfb,noadc overflows,0x3fe 03jul08 3 rms=30 no pfb overflows,0x1ffa no pfb overflows,0xffd no pfb overflows, yes adcOver.0x3ff 03jul08 4

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