naudio SineWaveProvider32 gives clicks when changing Amplitude

Question

I am using naudio with SineWaveProvider32 code directly from http://mark-dot-net.blogspot.com/2009/10/playback-of-sine-wave-in-naudio.html to generate sine wave tones. The relevant code in the SineWaveProvider32 class:

public override int Read(float[] buffer, int offset, int sampleCount)
        {
            int sampleRate = WaveFormat.SampleRate;
            for (int n = 0; n < sampleCount; n++)
            {
                buffer[n + offset] =
                    (float)(Amplitude * Math.Sin((2 * Math.PI * sample * Frequency) / sampleRate));
                sample++;
                if (sample >= sampleRate) sample = 0;
            }
            return sampleCount;
        }

I was getting clicks/beats every second, so I changed

if (sample >= sampleRate) sample = 0;

to

if (sample >= (int)(sampleRate / Frequency)) sample = 0;

This fixed the clicks every second (so that "sample" was always relative to a zero-crossing, not the sample rate).

However, whenever I set the Amplitude variable, I get a click. I tried setting it only when the buffer[] was at a zero-crossing, thinking that a sudden jump in amplitude might be causing the problem. That did not solve the problem. I am setting the Amplitude to values between 0.25 and 0.0

I tried adusting the latency and number of buffers as suggested in NAudio change volume in runtime but that had no effect either.

My code that changes the Amplitude:

public async void play(int durationMS, float amplitude = .25f)
        {
        PitchPlayer pPlayer = new PitchPlayer(this.frequency, amplitude);
            pPlayer.play();
            await Task.Delay(durationMS/2);
            pPlayer.provider.Amplitude = .15f;
            await Task.Delay(durationMS /2);
            pPlayer.stop();
    }

Mark Heath Mark Heath · Accepted Answer · 2016-09-08T21:38:31

the clicks are caused by a discontinuity in the waveform. This is hard to fix in a class like this because ideally you would slowly ramp the volume from one value to the other. This can be done by modifying the code to have a target amplitude, and then if the current amplitude is not equal to the target amplitude then you move towards it by a small delta amount calculated each time through the loop. So over a period of say 10ms, you move from the old to new amplitude. But you'd need to write this yourself unfortunately.

For a similar concept where the frequency is being changed gradually rather than the amplitude, take a look at my blog post on portamento in NAudio.

naudio SineWaveProvider32 gives clicks when changing Amplitude

2 Answers