Android 中的实时音频处理
我正在使用 AudioRecord.read 将 PCM 数据捕获为字节。 但是，我发现它限制了初始化具有至少 3904 个缓冲区的 AudioRecord 对象。其中采样率为44100。 由于我需要对数据执行 FFT，因此我将样本增加到 4096。 因此，回调每 40-60 毫秒运行一次，将 setPositionNotificationPeriod 设置为 500。由于进一步减少持续时间，因此不会进行任何更改。 我想知道以下配置是否是最快的回调时间？
采样率：44100
通道：单声道
编码：PCM 16 BIT
缓冲区大小：4096
（我不确定它是 4096 还是 2048，因为我每次读取 4096 字节，它只能填充 2048 2 字节缓冲区）
即使 40-60ms 也是可以接受的，然后我执行 FFT，最终阻止每个回调大约 200-300 毫秒。而且仍然存在很多影响精度的噪声。 我正在使用这些源代码： FFT in Java 和 < a href="http://introcs.cs.princeton.edu/java/97data/Complex.java.html" rel="nofollow">复杂类
是否还有其他执行快速、可靠且消耗的选择较少的内存处理FFT？ 我发现上面的类新了太多对象并弹出大量垃圾收集消息。
总之，我有 3 个问题：
- 初始 bufferSize 是否等于我可以从 .read 方法读取的缓冲区？
- 40-60ms 是捕获 44100 采样率音频数据的限制吗？
- 您能否推荐一些 FFT 库，以便我在处理 FFT 时可以有更好的性能？ （我认为使用C代码库是否更好？）
抱歉我的英语不好，也感谢您花时间回答我的问题。
PS我在iOS上尝试过，它只能以44100采样率采集512个样本。所以每次回调只需要大约10ms。
I am using AudioRecord.read to capture PCM data to bytes.
However, I found that it restricted to initialize the AudioRecord object with at least 3904 buffers. Where the sampling rate is 44100.
Since I need to perform FFT of the data so I increased the samples to 4096.
As a result, the callback runs every 40-60ms by setPositionNotificationPeriod to 500. Since a further decrease the duration doesn't make any changes.
I'm wondoring if it is the fastest callback time with below configuration?
Sampling Rate: 44100
Channel: Mono
Encoding: PCM 16 BIT
BufferSize: 4096
(Im not sure if it is 4096 or 2048 since I read 4096 bytes every time and it can only fill 2048 2bytes buffer)
even 40-60ms is acceptable, I then perform FFT which eventually block each callback around 200-300ms. And there is still many noise affecting the accuracy.
I'm using these source code: FFT in Java and Complex class
Is there any other choice that perform fast, reliable and consume less memory processing FFT?
I found that the above classes new too much objects and pop up loads of gragarbage collection's messages.
In conclude, I have 3 questions:
- Is the initial bufferSize equal to the buffers that I can read from the .read method?
- Is 40-60ms the limitation to capture audio data with 44100 sampling rate?
- Could you suggest some FFT library so that I can have a better performance in processing FFT? (I think if it is better to use C code library?)
Sorry for my bad english, also thank you for spending your time on my question.
P.S I tried it on iOS and it can just take 512 samples with 44100 sampling rate. So every callback takes around 10ms only.
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关于问题＃3：也许不如本机库那么快，但我已经开始使用这些类，并且它们似乎适合实时工作（尽管我是从文件而不是麦克风中读取）：FFPack。
最常见的本机库是 KissFFT，您可以找到它作为 libGDX 的一部分针对 Android 编译的库。
Regarding question #3: Maybe not as fast as a native library, but I've started using these classes, and they seem to be fine for real-time work (although I am reading from files, not the microphone): FFTPack.
The most common native library is KissFFT, which you can find compiled for Android as part of libGDX.