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@ -24,6 +24,11 @@ |
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* The sign of the coefficients for feedback, the a[], here use the |
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* convention of the ARM CMSIS library. Matlab reverses the signs of these. |
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* I believe these are treated per those rules!! Bob |
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*
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* Algorithm for CMSIS library |
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* Each Biquad stage implements a second order filter using the difference equation: |
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* y[n] = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] |
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* The a1 and a2 coeccicients do not have minus signs as do the Matlab ones. |
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*/ |
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#ifndef _filter_iir_f32 |
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@ -182,6 +187,8 @@ class AudioFilterBiquad_F32 : public AudioStream_F32 |
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setCoefficients(stage, coeff); |
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} |
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// frequency in Hz. q makes the response stay close to 0.0dB until
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// close to the notch frequency. q up to 100 or more seem stable.
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void setNotch(uint32_t stage, float frequency, float q) { |
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double coeff[5]; |
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double w0 = frequency * (2 * 3.141592654 / sampleRate_Hz); |
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