Clicking (clipping?) with lpf

[nrb...@nyu.edu]

Hi all,

I made a group of oscillators with the code found below ( I also attached the sketch mozzi_trial3.ino). I am trying to use a low pass filter on the group of oscillators called "out." In updateControl(), when I replace the last line with the second to last line (replace return (int) out; with return (int) lpf.next(out); I don't hear the oscillators being passed through a low pass filter, but rather a series of clicks on top of the unfiltered sound. I've attached two (my apologies: due to weird circumstances I had to record the audio with a field recorder listening to laptop speakers) audio clips showing what I hear, so you don't have to build the circuit. The circuit is simply the arduino pin9 running to a headphone jack's hot pin and the jack's pin grounded to the arduino. Thank you in advance for any assistance/advice! It's much appreciated. -Nick 

The code:

//drone in F minor

#include <MozziGuts.h>

#include <Oscil.h>

#include <tables/sin2048_int8.h>

#include <LowPassFilter.h>

#include <ReverbTank.h>

#define CONTROL_RATE 128

Oscil<2048, AUDIO_RATE> aSin1(SIN2048_DATA);

Oscil<2048, AUDIO_RATE> aSin2(SIN2048_DATA);

Oscil<2048, AUDIO_RATE> aSin3(SIN2048_DATA);

Oscil<2048, AUDIO_RATE> aSin4(SIN2048_DATA);

Oscil<2048, AUDIO_RATE> aSin5(SIN2048_DATA);

Oscil<2048, AUDIO_RATE> aSin6(SIN2048_DATA);

Oscil<2048, AUDIO_RATE> aSin7(SIN2048_DATA);

Oscil<2048, AUDIO_RATE> aSin0(SIN2048_DATA);

Oscil<2048, CONTROL_RATE> kVol1(SIN2048_DATA);

Oscil<2048, CONTROL_RATE> kVol2(SIN2048_DATA);

Oscil<2048, CONTROL_RATE> kVol3(SIN2048_DATA);

Oscil<2048, CONTROL_RATE> kVol4(SIN2048_DATA);

Oscil<2048, CONTROL_RATE> kVol5(SIN2048_DATA);

Oscil<2048, CONTROL_RATE> kVol6(SIN2048_DATA);

Oscil<2048, CONTROL_RATE> kVol7(SIN2048_DATA);

Oscil<2048, CONTROL_RATE> kVol0(SIN2048_DATA);

Oscil<2048, CONTROL_RATE> kFilterMod(SIN2048_DATA);

char v1,v2,v3,v4,v5,v6,v7,v0;

LowPassFilter lpf;

void setup() {

  

  lpf.setResonance(1);

  byte cutoff_freq = 80;

  lpf.setCutoffFreq(cutoff_freq);

  

  aSin1.setFreq(174.61f); // F3

  aSin2.setFreq(196.0f); // G3

  aSin3.setFreq(207.65f); // Ab3

  aSin4.setFreq(233.08f); // Bb3

  aSin5.setFreq(261.63f); // C4

  aSin6.setFreq(277.18f); // Db

  aSin7.setFreq(311.13f); // Eb

  aSin0.setFreq(349.23f); // F4

  

  kVol1.setFreq(4.43f);

  kVol2.setFreq(0.0245f);

  kVol3.setFreq(0.019f);

  kVol4.setFreq(0.07f);

  kVol5.setFreq(0.047f);

  kVol6.setFreq(0.031f);

  kVol7.setFreq(0.0717f);

  kVol0.setFreq(0.041f);

  v1=v2=v3=v4=v5=v6=v7=v0=127;

  

  startMozzi(CONTROL_RATE);

}

void updateControl(){

   v1 = kVol1.next()>>1; // going at a higher freq, this creates zipper noise, so reduce the gain

   v2 = kVol2.next();

   v3 = kVol3.next();

   v4 = kVol4.next();

   v5 = kVol5.next();

   v6 = kVol6.next();

   v7 = kVol7.next();

   v0 = kVol0.next();

}

int updateAudio(){

  long out =

      (long)

      aSin1.next()*v1 +

      aSin2.next()*v2 +

      aSin3.next()*v3 +

      aSin4.next()*v4 +

      aSin5.next()*v5 +

      aSin6.next()*v6 +

      aSin7.next()*v7 +

      aSin0.next()*v0;

      out >>= 9;

  //return (int) lpf.next(out);

  return (int) out;

}

void loop() {

  audioHook();

}

[Tim Barrass]

Hi nrb338,

it sounds like the processor can't keep up - have you tried reducing the number of oscillators?

Also, the filter resonance increases from 0 (none) to 255 (maximum).  This is not clearly documented (thanks for drawing my attention to it), but the examples have it around 200.  Your setting of 1 probably won't do much - also, the oscillators in the sketch aren't producing very high frequencies, so the filter might not be very dramatic even with higher resonances.

Tim

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