CODEWITHSUNDEEP
audiosignal-processingfft
user818117
user818117

Reputation: 420

discrete fourier transform frequency bound?

for a 8KHz wav sound i took 20ms sample which has 160 samples of data, plotted the FFT spectrum in audacity. It gave the magnitudes in 3000 and 4000 Hz as well, shouln't it be giving the magnitudes until the 80Hz,because there is 160 samples of data?

Upvotes: 0

Views: 382

Answers (3)

user818117
user818117

Reputation: 420

actually audacity shows the peaks as 4503Hz which means understands to 1Hz bins. by the way if I take 20ms and repeat it 50 times to make as 1s sample,is the fft going to be for 1Hz bins? and also audacity has the option for the window as far as I know If you use windowing then the components should be multiple times of 2,like 1,2,4,8,etc.. but it shows the exact frequencies,then why it uses the windowing?

Upvotes: 0

Amin Jalali
Amin Jalali

Reputation: 321

The best sampling rate is 2*frequency. in different frequencys you should to change the sampling rate.

Upvotes: -1

Paul R
Paul R

Reputation: 212929

For a sample rate of Fs = 8 khz the FFT will give meaningful results from DC to Nyquist (= Fs / 2), i.e. 0 to 4 kHz. The width of each FFT bin will be 1 / 20 ms = 50 Hz.

Upvotes: 4

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