Extracting a sinewave signal when characteristic phase and frequency are known

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Discussion Overview

The discussion revolves around the challenge of extracting the magnitude of a sinewave signal that is contaminated by noise, given that the phase and characteristic frequency are known. Participants explore various methods and considerations related to signal processing, including Fourier transforms, filtering, and curve fitting techniques.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests using a basic Fourier transform to obtain the magnitude at the characteristic frequency, but notes that the phase may be shifted.
  • Another participant proposes filtering out the noise and using peak detection or calculating the RMS of the signal to find the peak value.
  • A participant questions the concept of absolute phase in relation to a sine wave.
  • There is a suggestion to consider whether the issue is noise or possibly aliasing, with a recommendation to experiment with the sampling rate.
  • A participant references a method from Tom Irvine's work that involves a curve fitting technique to extract amplitude, frequency, and phase, indicating it may be useful for vibration analysis.
  • One participant mentions a numerical filter that could be applicable but cannot recall its name, and inquires about the nature of the noise (gaussian or normal).

Areas of Agreement / Disagreement

Participants express various approaches and considerations, but there is no consensus on a single method or solution to the problem. Multiple competing views remain regarding the best approach to extract the magnitude of the sinewave signal.

Contextual Notes

Participants have not resolved the assumptions regarding the nature of the noise or the implications of phase in sine waves. The discussion includes references to specific methods without detailed mathematical steps or definitions.

tchetch
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Hi there,

i have this problem:
I have a sinewave signal contaminated by a large amount of noise. I already know the phase of the signal and its characteristic frequency, and I am searching for its magnitude.

If I do a basic Fourier transform, I would obtain the magnitude at its characteristic frequency, but the phase would be generally shifted. Does anyone know a way to extract the magnitude at its specific phase and frequency ?

Thanks in advance
 
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Filter out the noise and then do peak detect? Or just take the RMS of the signal, and calculate the peak value (adding or subtracting an offset as necessary)?
 
I don't understand how a sine wave can have absolute phase?
 
Is it truly noise or have you considered it could be an aliasing issue? Have you treid playing with the sampling rate?
 
I was also looking through some old notes I have. Tom Irvine over at Vibrationdata.com published a quick paper regarding a method he wrote a small program for, called sinefind. The paper is entitled "Sine Function Identification and Removal." I can't post it here because it is Tom's work. It pulls out amplitude, frequency and phase by a curve fit method.

If you have any interest in vibration analysis, take a look over at Tom's website.

www.vibrationdata.com
 
There is a type of numerical filter than can do this, but the name escapes me right now. Is the noise gaussian or normal?
 

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