Tone control implementation

markatucla Question

May 6, 2024 00:00

I, too, am trying to implement a simple tone control. The strategy described here, using indexed filters, seems very straightforward, but it hasn't worked in my hands.

As best I can tell, I have the correct number formats. However, no sound passes through the system. Using the Stimulus/Probe pair, I can see the signal after the first T-Connector, but when I look after the output of the indexed filters, there is no signal present. I have tried using a variety of DSP read backs, and the numerical inputs to the filters appear to be intact (the numbers are displayed as though they are floats, but they tae on integer values (1.00000, 5.00000, etc...)

Might someone tell me what I'm doing wrong here?

Thanks so much for the support.

MiniPreamp.dspproj

MiniPreamp.dspproj54.4 KB

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DaveThib Reply

May 6, 2024 00:00

Hello markatucla,

Thanks for including your project. It is always so helpful.

First I want to mention that the stimulus and probe feature will not work with an indexed filter because SigmaStudio has no idea what filter is active in the DSP. The probe display is all calculated in SigmaStudio in the PC using the coefficients it knows about. You actually do not need the hardware for this to work which is about the only thing that works that way with the SigmaDSPs. So SigmaStudio does not know what filter is selected. Also, for others who might be using the Sigma300/350 parts, many of those filters the coefficients are calculated in the DSP not in SigmaStudio do the probe will not work there either.

You are having an issue with number formats. You need to send an integer format to the filter index. You are sending a HUGE number. The number coming into the control pin is used as a pointer offset so it needs to be an integer.

Here is an example project:

ADAU1701 AUXADC Index Selectable Filter.dspproj

Then I can suggest you watch some of my videos on a few different subjects that kind of got you.

Here is a list:

(+) ADAU1701 Capture Window, Params Tab and Sequencer window - Videos Published - Video Annex - EngineerZone (analog.com)

AUX ADCs (youtube.com)

This one is about Readbacks:

https://youtu.be/GDLhk1E-98A

Thanks,

Dave T

ADAU1701-AUXADC-Index-Selectable-Filter.dspproj162 KB

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markscohen Reply

May 7, 2024 00:00

Thank you. That clarified everything, and I have a working system. I had assumed that the indexed filter would have accepted a fixed DC value in my tests and therefore would have passed the Stimulus. The fact that I saw nothing with the Probe threw me off.