Stimuli/Probe: No response displayed

Hello Sachin,

Please take a look at this thread for a discussion of some cases where Stimulus/Probe may not work: Re: Index selectable filtering issue

The stimulus/probe will not work if certain nonlinear cells are placed between them. The reason is that a frequency response cannot be calculated if nonlinear cells or time-dependent cells would affect different frequencies in different ways over time.

It's possible that you have a block like that in your signal flow, which is causing the probe window to be blank.

Hello Brett,

Thank you for your response. Here is the signal flow (Please refer the attached screenshot). I was trying to measure the response between

A-X-B using the integrated tools of SigmaStudio. So this makes it obvious that SigmaStudio should know the transfer functions of all the modules in the signal chain to simulate the frequency response. I guess I will have to use an external measuring equipment to capture the frequency response.

Thank you for sharing the signal flow. Third-party licensed algorithms often use techniques such as psychoacoustic bass enhancement that modify the harmonic content of the signal. This kind of processing is very nonlinear, so it's impossible for SigmaStudio to calculate the frequency response.

So I guess state-variable filters also don't work with the stimulus/response? It would be nice if the response window at least showed an error message in this case instead of just doing nothing.

Hi J3627,

I tried the stimulus / probe with a state variable filter (bottom) and it worked, but it went blank with the homemade filter (top).

Bob

Oh, ok. I meant the state variable filter with F/Q inputs.

Yep, the stimulus / probe won't play with the voltage-controlled version of the filter. Since the filter itself is the same either way, apparently the stimulus / probe can't figure the control inputs -- in general these could be variables produced by other blocks, which would require a full simulation of the DSP core to establish.

Bob

I've since tested a number of situations with Stimulus - Probe, and made a tutorial on what it can and cannot do: Stimulus-Probe Capability and Limitations

HI all:

The one thing to keep in mind is that Stimuly and Probe transfer function (frequency response) can only be calculated when the information for calculating a transfer function lives and is generated in the PC. For example filters (coefficients) are first calculated on the PC and the passed on to the DSP. When the transfer function depend on variables generated inside the DSP, the PC doesn't have this knowledge and therefore cannot calculate the transfer function. For example Dynamics Processors, Adaptive Mixers, or any INDEX dependent or Voltage dependent block.

Hope this helps clarify the Stimuly-Probe functionality.

Miguel

Hi all,

I tried to use the Stimulus / Probe to test some filters, but it seems to only work once? I can plot the response once I start the Notch-Q-test.dspproj by pressing the Stimulus button and then the Probe button. If I press the Stimulus button again it doesn't work (blank response), also when I try other filters with the coefficients precalculated in SigmaStudio following the rules mentionned in https://ez.analog.com/message/120089#120089 it gives a blank response...

What am I doing wrong?

Can you please post the offending schematics?

Thank you

Miguel

The first time I open the schematic and press Stimulus and then Probe, it works.

The second time I press Stimulus and then Probe, it shows me a blank plot.

Thanks,

Vincent

Hello Vincent,

After choosing a ADAU1701 in HW Config, I tried your filter setup and the Stimulus-Probe tool worked every time. Repeating the experiment for a ADAU1452, I couldn't get a plot at all! Since this tool predicts filter responses without hardware, this makes little sense to me. Apparently the Sigma 300 compiler (used with the ADAU145x series DSPs) runs a different version of the tool. Here's two possible workarounds:

Experiment with your filter responses (via the simulation tool) using the ADAU1701 hardware choice, even if you're running a different DSP. My tutorial you cited above was based on testing with this choice.

Try using the Single-Precision version of the filter for simulation, even though you need Double-Precision when actually running signal. The ADAU1452 Single-Precision filter simulates fine in my tests.

Best regards,

Bob

Hi,

I did try the tool with the ADAU1701 in the HW config... Maybe the version of SigmaStudio I have has a bug that has been fixed in 3.11? I am using 3.10 x64. Since 3.11 x64 doesn't work well in my windows 7.

Thanks

Hello,

Try the latest beta, that's what I've been using.

Bob

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