real time audio processing and algebraic loop issues

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mdb 2015-11-16

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https://ww2.mathworks.cn/matlabcentral/answers/255084-real-time-audio-processing-and-algebraic-loop-issues

评论： mdb 2015-11-19

model2.mdl

Hi all, I'd like to emulate a "microphone channel" so in the model I attached there is an input from wav file (sampled at 48kHz), an amplifier, a sigma delta modulator (working at 3.6MHz so the OSR ratio is 75). If I try to simulate the model it works (meaning that simulation runs), but as soon as I connect at the output of the decimation filter a scope, a "save to wav file" block or whatever I get errors due to algebraic loop. I don't understand where this error is coming from and why it appears only if I connect something to the output. This problem make impossible to verifiy if the model is working fine and the audio at the ouput is the correct conversion of the input one and if the model is able to simulate audio file in real time. Thanks in advance for any help

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Answer 1

Puneet Rana 2015-11-16

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https://ww2.mathworks.cn/matlabcentral/answers/255084-real-time-audio-processing-and-algebraic-loop-issues#answer_200051

The algebraic loop is in SD2 subsystem. This will help you identify it: http://www.mathworks.com/help/simulink/ug/algebraic-loops.html#bsjdi74-1

Simulink by default will optimize out the unused blocks from Simulation. In this model, the subsystem SD2 has no sink block connected to its output, so it will be removed from simulation. When you connect a scope to its output, this subsystem cannot be removed and so the algebraic loop is reported. The sink block does not cause the algebraic loop - it only helped you see it.

If you turn off Block reduction from configuration parameters pane (see: http://www.mathworks.com/help/simulink/gui/optimization-pane-general.html#bq7cqwp-1), you will get the same error even with scopes commented out.

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mdb 2015-11-19

thanks for your reply, I got the point about the block reduction. I still can not solve the loop issues, every loop in SD2 has a delay and the initial condition is defined so I don't understand why the solver is not able to solve the system. Any suggestion is more than welcome

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