Hi Brent, Thanks for your response. please go through the below details we need help. Brief Details of our work: To the MSP ADC14 we fed a (0-0.625volt) peak to peak sine signal. The sine signal is addition of 520 Hz and 530 Hz sine waves. Both the sine signals have a 0-0.625volt peak to peak. The ADC of msp 432 has an external reference of 1.8 volts. Sampling rate of ADC is 10240 samples per second. we are taking 1600 samples which will take 1600*(1/10240) = 0.15625 seconds. cycle time of 520Hz signal is 0.00192 seconds, it is periodic in the 1600 samples window. number of samples taken are 1600. Below are the operations we performed: scale the ADC count with scaling factor 1.8/2^14 (msp432 has 14 bit ADC). Convert the scaled ADC value to Q15 format. pad 448 zeros to the converted 1600 samples of Q15 data. perform a 2048 point Q15 Real FFT on this data. calculate magnitude for 1024 samples in FFT output. Our observations are the peaks at frequency bins corresponding to 520 Hz bin and 530 Hz in FFT output. magnitude is 974 for both the bins.(1600 sample with padded zeros) If we take complete 2048 samples from ADC and perform FFT, the value of the peaks at 520 hz and 530 Hz is 1280 . 1280 * (1600/2048) = 1000 which is close to the peak for 1600 samples i.e. 974. But when we perform the same process on a sine signal(0-0.625 volt) which is an adition of 520Hz and 525Hz for 1600 samples. we get peak value of 809 at 520 hz bin and 525 hz bin. shouldn't it be 974 . Please help us to solve this. Our application is vibration analysis. Thanks in advance.
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