KVR Audio

quadsas · Post by **quadsas** » Fri Jan 17, 2014 4:09 pm

Basically, I am trying to build a simple 4 sine wave oscillator, but for some reason it clips. I've tried doing noobish attempt of reducing output to 1 (if >1, then outSample = 1), but it didn't work and also changed the sound. any ideas? mGain is value from 0 to 1, just controlling the volume of each wave.

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void VST_Plug_in::processReplacing (float** inputs, float** outputs, VstInt32 sampleFrames)
{
    float* out1 = outputs[0];
    float* out2 = outputs[1];

	float outSample = 0.0;
	float frequency = 0.0;

	for(int i = 0; i < sampleFrames; i++)
    {
		//create the sine wave output
		frequency = m_frequencyTable[m_currentNote];
		mSine1 = (float)sin(2.0*PI*frequency*m_time/m_sampleRate) * mGain1;
		mSine2 = (float)sin(2.0*PI*frequency*m_time/m_sampleRate) * mGain2;
		mSine3 = (float)sin(2.0*PI*frequency*m_time/m_sampleRate) * mGain3;
		mSine4 = (float)sin(2.0*PI*frequency*m_time/m_sampleRate) * mGain4;

		//multiply the sine by the velocity
		outSample = mSine1 + mSine2 + mSine3 + mSine4;
		outSample = (outSample * m_currentVelocity) ;


		//increment the time
		m_time++;

		// write samples to output buffer 
        out1[i] = outSample;
        out2[i] = outSample;
    }
}

brendano · Post by **brendano** » Fri Jan 17, 2014 4:25 pm

You want your outSample to be < 1. So divide your mGain* by the number of waves

quadsas · Post by **quadsas** » Fri Jan 17, 2014 4:36 pm

Yes, that does work to an extent, thank you.

Problem right now is that most notes clip when you play them (at the very start, for a few miliseconds you get that clip, and after that its fine). Is this an easily fixable problem?

helium · Post by **helium** » Fri Jan 17, 2014 4:48 pm

This

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      mSine1 = (float)sin(2.0*PI*frequency*m_time/m_sampleRate) * mGain1;
      mSine2 = (float)sin(2.0*PI*frequency*m_time/m_sampleRate) * mGain2;
      mSine3 = (float)sin(2.0*PI*frequency*m_time/m_sampleRate) * mGain3;
      mSine4 = (float)sin(2.0*PI*frequency*m_time/m_sampleRate) * mGain4;

      //multiply the sine by the velocity
      outSample = mSine1 + mSine2 + mSine3 + mSine4;
      outSample = (outSample * m_currentVelocity) ;

is equivalent to

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      mSine = (float)sin(2.0*PI*frequency*m_time/m_sampleRate);
      outSample = mSine * (mGain1 + mGain2 + mGain3 + mGain4) * m_currentVelocity;

.
So just make sure that "(mGain1 + mGain2 + mGain3 + mGain4) * m_currentVelocity" is allways ≤ 1.

MadBrain · Post by **MadBrain** » Fri Jan 17, 2014 5:27 pm

Reduce the volume of your synth.

mystran · Post by **mystran** » Fri Jan 17, 2014 6:06 pm

MadBrain wrote:Reduce the volume of your synth.

Indeed, that's usually the right solution.

Korhaan · Post by **Korhaan** » Fri Jan 17, 2014 7:44 pm

helium wrote:This

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      mSine1 = (float)sin(2.0*PI*frequency*m_time/m_sampleRate) * mGain1;
      mSine2 = (float)sin(2.0*PI*frequency*m_time/m_sampleRate) * mGain2;
      mSine3 = (float)sin(2.0*PI*frequency*m_time/m_sampleRate) * mGain3;
      mSine4 = (float)sin(2.0*PI*frequency*m_time/m_sampleRate) * mGain4;

      //multiply the sine by the velocity
      outSample = mSine1 + mSine2 + mSine3 + mSine4;
      outSample = (outSample * m_currentVelocity) ;

is equivalent to

Code: Select all

      mSine = (float)sin(2.0*PI*frequency*m_time/m_sampleRate);
      outSample = mSine * (mGain1 + mGain2 + mGain3 + mGain4) * m_currentVelocity;

.
So just make sure that "(mGain1 + mGain2 + mGain3 + mGain4) * m_currentVelocity" is allways ≤ 1.

As mentioned the 4 oscillators, since they have the same phase are just like one sine scaled up. You can see what they look like when no gain is applied to any of them.
http://www.wolframalpha.com/input/?i=si ... sin%28x%29
Limiting the output at one would turn this signal into a square wave:

quadsas · Post by **quadsas** » Sun Jan 19, 2014 10:11 pm

I don't have any big problems with clipping, thank you for your help. I've added some detuning and it sounds great. Afterwards I added a square wave, and now I've tried adding sawtooth, but somethings not working. it just doesn't seem to generate saw wave, just a highpitched sound. Formula is below, seems to like somethings wrong with time/sampleRate thing.

mSawt = 2*frequency*(m_time / m_sampleRate-(float)floor(m_time / m_sampleRate+0.5*frequency)) * (mGain6 / 6);

Korhaan · Post by **Korhaan** » Mon Jan 20, 2014 7:22 pm

Your function is for a sawtooth, but it is not within the range -1 to 1 and does not show the intended frequency. One thing that I can see is that you are scaling your result by the waveform's frequency, which will cause an issue. Also, going by your previous question I am assuming your m_time variable is in samples since you scale it down by m_sampleRate in your sine waveform generation. You are missing the division by the waveform's period, or 1 / frequency. See this wikipedia article on sawtooth generation. http://en.wikipedia.org/wiki/Sawtooth_wave

Specifically the formula:
x(t) = 2 * (t / a - floor(1/2 + t/a))

using your variables this translates to:
m_time_in_seconds = m_time / m_sampleRate
x(m_time_in_seconds) = 2 * ((m_time_in_seconds / (1 / frequency)) - floor(1/2 + (m_time_in_seconds/(1 / frequency))))

Here is an example sawtooth generation function in python for reference

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def generate_sawtooth(seconds, sample_rate, frequency, gain):
	total_sample_count = sample_rate * seconds
	time_steps_seconds = [x / sample_rate for x in range(0, total_sample_count)]
	period = 1 / frequency
	samples = [(2 * (x / period - math.floor(0.5 + x / period)) * gain) for x in time_steps_seconds]
	return samples

basic 4 sine wave oscillator clips