MATLAB: THD calculation using FFT tool and mathematically

fftthd

i used the FFT tools to compute the THD and it gave me a certain value. then, when i calculated the THD using a mathematical equation i got a different value. So, please i want to know how the FFT tools of powergui compute the THD. i.e, by which equation it calculate the THD?

Best Answer

Do you have Signal Processing Toolbox? If you do, see the function thd()

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MATLAB: How to use spectrum analyzer object to show a signal waveform

You can set FrequencyResolutionMethod to 'Window length' to manually adjust the length of signal used to compute the spectrum, e.g.,

Fs = 2500; 
Sineobject1 = dsp.SineWave('SamplesPerFrame',1024,'SampleRate',Fs,'Frequency',100); 
Sineobject2 = dsp.SineWave('SamplesPerFrame',1024,'SampleRate',Fs,'Frequency',1000); 
SA = dsp.SpectrumAnalyzer('SampleRate',Fs,'NumInputPorts',2,'PlotAsTwoSidedSpectrum',... 
    false,'ChannelNames',{'SinewaveInput','NotchOutput'},'ShowLegend',true,...
    'FrequencyResolutionMethod','WindowLength');
step(SA,step(Sineobject1),step(Sineobject2))

MATLAB: How to specify overlap in dsp.SpectrumEstimator object

Overlap property does not exist in the 'dsp.SpectrumEstimator' object as of MATLAB R2017a. To implement the overlap option there are two options -

1. Use the 'dsp.AsyncBuffer' object to capture the overlapped frame and then step that through the object 'dsp.SpectrumEstimator'. This object was introduced in R2017a.

2. Using vector indexing, manually divide the input signal into frames including the overlapping samples. Then step these frames through the 'dsp.SpectrumEstimator', one at a time.

Please refer to the attached script which shows the use of 'dsp.AsyncBuffer' object to implement the overlap in 'dsp.SpectrumEstimator' and obtain the equivalent spectrum as obtained from 'pwelch'.

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Related Solutions

MATLAB: How to use spectrum analyzer object to show a signal waveform

MATLAB: How to specify overlap in dsp.SpectrumEstimator object

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