Question about SGTL5000 and using the parametric EQ (calcBiquad() and eqFilter())

[C0d3man]

Hi,

I am trying to use the EQ from the SGTL5000 audio shield as a 7-band parametric eq. But I have trouble with the eqFilter() function (or calcBiquad()). calcBiquad() seems to have not much documentation, so one of my problem might be using a wrong parameter range. Here is my code:

Header of a new class inherits from AudioControlSGTL5000:

class AudioControlSGTL5000Plus : public AudioControlSGTL5000
{
  public:
    AudioControlSGTL5000Plus(uint8_t n = 7) {
      num_bands = constrain(n, 1, 7);
      init_parametric_eq();
    };
    void setEQType(uint8_t band, uint8_t ft);
    void setEQFc(uint8_t band, float frq);
    void setEQQ(uint8_t band, float q);
    void setEQGain(uint8_t band, float gain);
    void commitFilter(uint8_t band);

  private:
    void init_parametric_eq(void);
    uint8_t num_bands;
    uint8_t* filter_type;
    float* Fc;
    float* Q;
    float* peakGainDB;
};

#define EQ_TYPE_0 FILTER_PARAEQ
#define EQ_CENTER_FRQ_0 50.0
#define EQ_Q_0 1.0

#define EQ_TYPE_1 FILTER_PARAEQ
#define EQ_CENTER_FRQ_1 120.0
#define EQ_Q_1 1.0

#define EQ_TYPE_2 FILTER_PARAEQ
#define EQ_CENTER_FRQ_2 220.0
#define EQ_Q_2 1.0

#define EQ_TYPE_3 FILTER_PARAEQ
#define EQ_CENTER_FRQ_3 1000.0
#define EQ_Q_3 1.0

#define EQ_TYPE_4 FILTER_PARAEQ
#define EQ_CENTER_FRQ_4 2000.0
#define EQ_Q_4 1.0

#define EQ_TYPE_5 FILTER_PARAEQ
#define EQ_CENTER_FRQ_5 7000.0
#define EQ_Q_5 1.0

#define EQ_TYPE_6 FILTER_PARAEQ
#define EQ_CENTER_FRQ_6 10000.0
#define EQ_Q_6 1.0

... and the class implementation:

void AudioControlSGTL5000Plus::init_parametric_eq(void)
{
  //eqSelect(PARAMETRIC_EQUALIZER);
  //eqFilterCount(num_bands);

  filter_type = new uint8_t[num_bands];
  Fc = new float[num_bands];
  Q = new float[num_bands];
  peakGainDB = new float[num_bands];

  setEQType(1, EQ_TYPE_0);
  setEQFc(1, EQ_CENTER_FRQ_0);
  setEQQ(1, EQ_Q_0);
  setEQGain(1, 0.0);

  if (num_bands > 1)
  {
    setEQType(2, EQ_TYPE_1);
    setEQFc(2, EQ_CENTER_FRQ_1);
    setEQQ(2, EQ_Q_1);
    setEQGain(2, 0.0);
    commitFilter(7);
  }

  if (num_bands > 2)
  {
    setEQType(3, EQ_TYPE_2);
    setEQFc(3, EQ_CENTER_FRQ_2);
    setEQQ(3, EQ_Q_2);
    setEQGain(3, 0.0);
    commitFilter(7);
  }

  if (num_bands > 3)
  {
    setEQType(4, EQ_TYPE_3);
    setEQFc(4, EQ_CENTER_FRQ_3);
    setEQQ(4, EQ_Q_3);
    setEQGain(4, 0.0);
    commitFilter(7);
  }

  if (num_bands > 4)
  {
    setEQType(5, EQ_TYPE_4);
    setEQFc(5, EQ_CENTER_FRQ_4);
    setEQQ(5, EQ_Q_4);
    setEQGain(5, 0.0);
    commitFilter(7);
  }

  if (num_bands > 5)
  {
    setEQType(6, EQ_TYPE_5);
    setEQFc(6, EQ_CENTER_FRQ_5);
    setEQQ(6, EQ_Q_5);
    setEQGain(6, 0.0);
    commitFilter(7);
  }

  if (num_bands > 6)
  {
    setEQType(7, EQ_TYPE_6);
    setEQFc(7, EQ_CENTER_FRQ_6);
    setEQQ(7, EQ_Q_6);
    setEQGain(7, 0.0);
    commitFilter(7);
  }
}

void AudioControlSGTL5000Plus::setEQType(uint8_t band, uint8_t ft)
{
  if (filter_type)
  {
    band = constrain(band, 1, num_bands);
    filter_type[band - 1] = ft;
  }
}

void AudioControlSGTL5000Plus::setEQFc(uint8_t band, float frq)
{
  if (Fc)
  {
    band = constrain(band, 1, num_bands);
    Fc[band - 1] = frq;
  }
}

void AudioControlSGTL5000Plus::setEQQ(uint8_t band, float q)
{
  if (Q)
  {
    band = constrain(band, 1, num_bands);
    Q[band - 1] = q;
  }
}

void AudioControlSGTL5000Plus::setEQGain(uint8_t band, float gain)
{
  if (peakGainDB)
  {
    band = constrain(band, 1, num_bands);
    peakGainDB[band - 1] = gain;
  }
}

void AudioControlSGTL5000Plus::commitFilter(uint8_t band)
{
  int filter[5] = {0, 0, 0, 0, 0};

  band = constrain(band, 1, num_bands);

  calcBiquad(filter_type[band - 1], Fc[band - 1], peakGainDB[band - 1],  Q[band - 1],  524288,  AUDIO_SAMPLE_RATE, filter);
  eqFilter(band, filter);
}

Here is a piece of code which uses this class:

...    
AudioControlSGTL5000Plus sgtl5000(7);
...
    sgtl5000.setEQFc(1, 1000.0);
    sgtl5000.setEQGain(1, 3.0);
    sgtl5000.setEQQ(1,0 6.0);
    sgtl5000.commitFilter(1);
...

But I am unsure what is the range and unit for Q and peakGainDB? Also my program crashes when running eqFilter(band, filter)

Has anyone an idea what I am doing wrong?

If it is important: The program runs on a T_4.1.

TIA, Holger

 

[C0d3man]

I added a simple test sketch available at https://codeberg.org/dcoredump/EQTest. All you need is a Teensy audio shield. Perhaps someone can help with this...