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Jeppe Clausen
Jeppe Clausen
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I'm having a problem where I cannot explain why the amplitude in the frequency domain not is as expected.

The scenario:

I have a time domain signal of consisting of two sine waves. on at 5Hz with amplitude 2 and one at 10Hz with amplitude 2. the signal is 10 seconds long. The 5 Hz sine wave is only present the first 5 seconds, and the 10Hz sine is only present in the last 5 seconds.

if I take an FFT of the first 5 seconds the amplitudemagnitude in the frequency domain at 5Hz is as expected. And again if I take an FFT of the last 5 seconds the amplitudemagnitude of the last 5 seconds is as expected.

But if I take the FFT of the entire signal both the amplitudemagnitude at 5 and 10 Hz seems to have halfed in amplitudemagnitude ? Is this expected or am I doing something wrong.

I'm using MathDotNet in a custom made application.

I'm having a problem where I cannot explain why the amplitude in the frequency domain not is as expected.

The scenario:

I have a time domain signal of consisting of two sine waves. on at 5Hz with amplitude 2 and one at 10Hz with amplitude 2. the signal is 10 seconds long. The 5 Hz sine wave is only present the first 5 seconds, and the 10Hz sine is only present in the last 5 seconds.

if I take an FFT of the first 5 seconds the amplitude in the frequency domain at 5Hz is as expected. And again if I take an FFT of the last 5 seconds the amplitude of the last 5 seconds is as expected.

But if I take the FFT of the entire signal both the amplitude at 5 and 10 Hz seems to have halfed in amplitude? Is this expected or am I doing something wrong.

I'm using MathDotNet in a custom made application.

I'm having a problem where I cannot explain why the amplitude in the frequency domain not is as expected.

The scenario:

I have a time domain signal of consisting of two sine waves. on at 5Hz with amplitude 2 and one at 10Hz with amplitude 2. the signal is 10 seconds long. The 5 Hz sine wave is only present the first 5 seconds, and the 10Hz sine is only present in the last 5 seconds.

if I take an FFT of the first 5 seconds the magnitude in the frequency domain at 5Hz is as expected. And again if I take an FFT of the last 5 seconds the magnitude of the last 5 seconds is as expected.

But if I take the FFT of the entire signal both the magnitude at 5 and 10 Hz seems to have halfed in magnitude ? Is this expected or am I doing something wrong.

I'm using MathDotNet in a custom made application.

Source Link
Jeppe Clausen
Jeppe Clausen
  • 111
  • 2

Amplitude in frequency domain not as expected with discontinues time domain signal

I'm having a problem where I cannot explain why the amplitude in the frequency domain not is as expected.

The scenario:

I have a time domain signal of consisting of two sine waves. on at 5Hz with amplitude 2 and one at 10Hz with amplitude 2. the signal is 10 seconds long. The 5 Hz sine wave is only present the first 5 seconds, and the 10Hz sine is only present in the last 5 seconds.

if I take an FFT of the first 5 seconds the amplitude in the frequency domain at 5Hz is as expected. And again if I take an FFT of the last 5 seconds the amplitude of the last 5 seconds is as expected.

But if I take the FFT of the entire signal both the amplitude at 5 and 10 Hz seems to have halfed in amplitude? Is this expected or am I doing something wrong.

I'm using MathDotNet in a custom made application.