编程

每天一点点音视频_AudioTrack播放动态生成的声波_1

本来想来写播放动态生成的声波，昨天晚上失眠，想了想如何生成声波，于是，更失眠了。

这篇文章我们来写一个生成声波的函数， 所谓函数，是这个样子的：

振幅 = f(时间)

简化问题，我们生成正弦波， 先把正弦波的参数列一下：

  1. 时间
  2. 振幅
  3. 最大振幅
  4. 周期（频率）

以上的参数，也就是数据

剩下的是算法， 既然是正弦波， 肯定与 sin() 有关

最终的结果如下：

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class WaveGenerator(val maxAmplitude: Float, val rate: Int) {
    fun getAmplitude(time: Float): Float {
        val cycle = PI.toFloat() * 2
        val radiansPerSecond = rate * cycle
        return sin(time * radiansPerSecond) * maxAmplitude
    }
}

我使用了单元测试，爽！！

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@Test
fun `计算某个时间点的振幅`() {
    generator = WaveGenerator(1f, RATE_ONE)

    assertThat(generator.getAmplitude(0f)).isWithin(0.001f).of(0f)
    assertThat(generator.getAmplitude(0.25f)).isWithin(0.001f).of(1f)
    assertThat(generator.getAmplitude(0.5f)).isWithin(0.001f).of(0f)
    assertThat(generator.getAmplitude(0.75f)).isWithin(0.001f).of(-1f)
    assertThat(generator.getAmplitude(1f)).isWithin(0.001f).of(0f)

    generator = WaveGenerator(1f, RATE_TWO)

    assertThat(generator.getAmplitude(0f)).isWithin(0.001f).of(0f)
    assertThat(generator.getAmplitude(0.25f)).isWithin(0.001f).of(0f)
    assertThat(generator.getAmplitude(0.5f)).isWithin(0.001f).of(0f)
    assertThat(generator.getAmplitude(0.75f)).isWithin(0.001f).of(0f)
    assertThat(generator.getAmplitude(1f)).isWithin(0.001f).of(0f)
    assertThat(generator.getAmplitude(0.125f)).isWithin(0.001f).of(1f)
    assertThat(generator.getAmplitude(0.375f)).isWithin(0.001f).of(-1f)

}

到点了，明天见