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Live Q&A Discussion - Frequency Domain Signal Processing

John Edwards - Watch Now - DSP Online Conference 2020 - Duration: 27:13

This is a the live Q&A session for the talk given by John Edwards and titled 'Frequency Domain Signal Processing'
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john.edwardsSpeaker
Score: 0 | 4 years ago | no reply

Here are answers to the questions that we did not have time to answer in the live session.
From Evan
Two questions:

  1. Are cascaded integrator comb filters the type typically used for
    on-chip sigma-delta data converters (decimator for ADC, interpolator for
    DAC)?
    Yes, they are exactly the same.

  2. Overlap-add vs overlap-save, is there a difference in effective
    filter response, since overlap-add isn't exactly the same operation as
    the fully time-domain convolution operation?
    Overlap-add, overlap-save and time domain convolution will all give exactly the same result.

From Chris Bore
In medical radar applications, using VNA (Vector Network Analyzer) the measurements are of CW signals, in I and Q (amplitude and phase, or complex phasor) - but most commonly FFTed to time domain pulse because that is what the radar engineers are used to - tell me that makes no sense?
In a CW application, the phase should give you the delay, if that is what you are looking for.

From Michael Kirkhart
Might this be the app note?
http://xanthippi.ceid.upatras.gr/people/psarakis/courses/DSP_APL/demos/APR8-sigma-delta.pdf
Yes, that it the one. Thank you, Michael.

From Jonathan Bramwell
When filtering in the frequency domain should you window the time domain data prior to fft. and does the choice of windowing function effect the filter response?
Excellent question. If you are using one of the overlap methods then the iFFT on the output unrolls the windowing effects from the input so you do not need to use a window.

From Ali Ficici
I have designed CIC filters for large interpolation or decimation rates. They are efficient but the BW of the signal needs to be fairly small compared to fs because of the droop in the filter.
That is absolutely correct, Ali, which is why the standard FIR filter after the CIC filters will typically have a slightly non-flat pass-band to compensate for the CIC roll-off.

From km
is the phase role implementation you mentioned for delay compensation? if so could you expand?
Yes. Phase roll is an artefact of satellite communications where the up and down links have slight errors in their frequencies that can lead to problems with echo cancellers etc.
The phase roll simulator converted time domain signals to the frequency domain, rotated the phase and then converted back to the time domain.
This was used to develop an algorithm to detect and compensate for phase roll, in the ground based modems.

From Arthur Lobo
Can you briefly discuss Generalized Cross Correlation?
Hi Arthur, sorry we didn't have time to discuss this live.
This is a big subject so I would recommend the follwing links:
https://en.wikipedia.org/wiki/Cross-correlation
https://www.dspguide.com/
The DSP Guide is a particularly good DSP reference.
If anyone has any more questions then please do not hesitate to get in touch : jedwards@numerix-dsp.com
Enjoy the rest of the conference,
John

11:00:57	 From  Evan : Two questions:

1. Are cascaded integrator comb filters the type typically used for on-chip sigma-delta data converters (decimator for ADC, interpolator for DAC)?

2. Overlap-add vs overlap-save, is there a difference in effective filter response, since overlap-add isn't exactly the same operation as the fully time-domain convolution operation?
11:02:19	 From  mnapier : Lenard I would be interested in that paper.
11:04:00	 From  Chris Bore : In medical radar applications, using VNA (Vector Network Analyzer) the measurements are of CW signals, in I and Q (amplitude and phase, or complex phasor) - but most commonly FFTed to time domain pulse because that is what the radar engineers are used to - tell me that makes no sense?
11:04:56	 From  Michael Kirkhart : Might this be the app note?
11:05:00	 From  Michael Kirkhart : http://xanthippi.ceid.upatras.gr/people/psarakis/courses/DSP_APL/demos/APR8-sigma-delta.pdf
11:05:49	 From  Jonathan Bramwell : When filtering in the frequency domain should you window the time domain data prior to fft. and does the choice of windowing function effect the filter response?
11:06:17	 From  Ali Ficici : I have designed CIC filters for large interpolation or decimation rates. They are efficient but the BW of the signal needs to be fairly small compared to fs because of the droop in the filter. 
11:07:26	 From  Evan : thanks!
11:13:10	 From  Timothy Young : Thanks for a great talk!
11:19:42	 From  christophe Blouet : the FFT should provide you accurate frequency and phase, the phase gives very good information on the timing
11:20:04	 From  christophe Blouet : and it's possible to go beyond FFT resolution
11:20:07	 From  Michael Kirkhart : No problem
speakers to learn to say "let's take this offline' quicker
11:28:47	 From  Leo : Very interesting session
11:28:50	 From  Leo : thank you very much
11:29:00	 From  Ali Ficici : thanks John!
11:29:15	 From  Arthur Lobo : Thank you

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