Many of us seem to slowly migrate from dedicated distortion measuring equipment (HP, Tek, AP) to software based solutions based on a sound card.
One feature I always valued on the dedicated equipment was that you can look at the distortion residual, basically the waveform coming out of the fundamental rejection filter.
If you know how to interprete that residual, you can tell a lot about what is going on in the DUT.
With software/sound card solutions this feature is lost.
But does it have to be?
The software involved effortlessly switches between frequency (FFT) and time domain views.
On idea I had is this: you look at the FFT of the signal, and digitally remove whatever is in the fundamental's bin. Then you take the result, convert it back to the time domain and presto! that is the distortion residual.
You can then show it on the PC or send it out through the other soundcard analog output so you can put it on a 'scope.
As far as I know, nobody has done this. Is there a good reason why it isn't done, or is it a case that nobody thought about it yet?
Comments?
jan
One feature I always valued on the dedicated equipment was that you can look at the distortion residual, basically the waveform coming out of the fundamental rejection filter.
If you know how to interprete that residual, you can tell a lot about what is going on in the DUT.
With software/sound card solutions this feature is lost.
But does it have to be?
The software involved effortlessly switches between frequency (FFT) and time domain views.
On idea I had is this: you look at the FFT of the signal, and digitally remove whatever is in the fundamental's bin. Then you take the result, convert it back to the time domain and presto! that is the distortion residual.
You can then show it on the PC or send it out through the other soundcard analog output so you can put it on a 'scope.
As far as I know, nobody has done this. Is there a good reason why it isn't done, or is it a case that nobody thought about it yet?
Comments?
jan