安卓：正弦波生成 [英] Android: Sine Wave Generation

问题描述

我试图用AudioTrack产生正弦波，方波和锯齿波。但是，这是建立在音频听起来并不像一个纯粹的正弦波，但喜欢它有某种重叠等浪潮。我将如何去获得纯净的正弦波状的第二code例如，当使用在我的第一个例子中的方法？由于顶部的例子只是移动周围的一些在第二次使用的算术，不应该他们产生一个相同的波？

I'm trying to use AudioTrack to generate sine, square, and sawtooth waves. However, the audio this is creating doesn't sound like a pure sine wave, but like it has some kind of other wave overlayed. How would I go about getting the pure sine wave like in the second code example, while using the method in my first example? Since the top example only moves around some of the arithmetic used in the second, shouldn't they produce an identical wave?

@Override
        protected Void doInBackground(Void... foo) {
            short[] buffer = new short[1024];
            this.track = new AudioTrack(AudioManager.STREAM_MUSIC, 44100, AudioFormat.CHANNEL_CONFIGURATION_MONO, AudioFormat.ENCODING_PCM_16BIT, minBufferSize, AudioTrack.MODE_STREAM);
            float samples[] = new float[1024];

            this.track.play();

            while (true) {
                for (int i = 0; i < samples.length; i++) {
                    samples[i] = (float) Math.sin( (float)i * ((float)(2*Math.PI) * frequency / 44100));    //the part that makes this a sine wave....
                    buffer[i] = (short) (samples[i] * Short.MAX_VALUE);
                }
                this.track.write( buffer, 0, samples.length );  //write to the audio buffer.... and start all over again!

            }           
        }

注：这确实给了我一个纯正弦波：

Note: This does give me a pure sine wave:

@Override
        protected Void doInBackground(Void... foo) {
            short[] buffer = new short[1024];
            this.track = new AudioTrack(AudioManager.STREAM_MUSIC, 44100, AudioFormat.CHANNEL_CONFIGURATION_MONO, AudioFormat.ENCODING_PCM_16BIT, minBufferSize, AudioTrack.MODE_STREAM);
            float increment = (float)(2*Math.PI) * frequency / 44100; // angular increment for each sample
            float angle = 0;
            float samples[] = new float[1024];

            this.track.play();

            while (true) {
                for (int i = 0; i < samples.length; i++) {
                    samples[i] = (float) Math.sin(angle);   //the part that makes this a sine wave....
                    buffer[i] = (short) (samples[i] * Short.MAX_VALUE);
                    angle += increment;
                }
                this.track.write( buffer, 0, samples.length );  //write to the audio buffer.... and start all over again!

            }           
        }

由于马亭：问题是，该波是越来越在缓冲波长之间切断。增加缓冲区大小解决了第二示例中的问题。看来，Math.PI * 2算术是最密集的循环，使价值移动到正在只计算一次外部变量解决一切

Thanks to Martijn: The problem is that the wave is getting cut off between wavelengths in the buffer. Increasing the buffer size solves the problem in the second example. It appears that the Math.PI * 2 arithmetic was the most intensive of the loop, so moving that value to an external variable that is only computed once solves everything.

推荐答案

尝试

1. 在增加缓冲区大小
2. prepare缓冲一次，并保持它重写到输出流（这将需要一些数学计算用于缓冲完美的大小，以确保整个正弦波非常适合在它）。

为什么呢？因为我怀疑缓冲区采取长期以prepare，是什么原因导致的两个缓冲滞后推到大，这可能会导致噪音。

Why? Because I suspect the buffer to taking to long to prepare, what causes a lag between two buffer pushes to big, which might be causing the noise.

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