预放大音频 OS X
OS X 有两个应用程序允许您在硬件播放音频之前对其进行预放大：Audio Hijack（预放大特定应用程序的输出）和 Boom（预放大所有系统音频）。这些应用程序的工作原理是在将音频流发送到声卡之前，对预先存在的音频流应用均衡（具有高前置放大器设置）。
我的问题是：如何劫持系统音频流然后将其发送到声卡。这是 API 中的某个地方，还是需要更改系统库？
There are two apps for OS X that allow you to pre-amplify audio before it gets played by the hardware: Audio Hijack (pre-amplifies output from particular applications) and Boom (pre-amplifies all system audio). These apps work by applying equalization to pre-existing audio streams - with a high pre-amp setting - before they are sent to the sound card.
My question is: how to hijack the system audio stream and then send it along to the sound card. Is this somewhere in an API, or would it require altering a system library ?
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1) 创建一个显示在音频系统首选项中的标准声音设备。这必须采用内核扩展 (kext) 的形式。仅通过阅读苹果文档很难创建 - 尝试查看一个名为 Soundflower 的应用程序。
2) 加载 kext 并拥有新的音频设备后，请在首选项中将其选择为系统音频的默认输出设备。
3) 现在您需要更改音频并将其通过管道传输到真实系统输出。这可以在随附的应用程序中完成，该应用程序将回调“IOProc”函数添加到 a) 新设备和 b) 计算机的内置输出设备。然后，您可以将音频缓冲区从一台设备复制到另一台设备，以将音频传输到扬声器。要增加容量，请将缓冲区中的所有字节乘以某个系数。请参阅 Soundflower 的随附应用程序。
1) Create a standard sound device that shows up in audio system preferences. This has to be in the form of a kernel extension (kext). Difficult to create by just reading apple docs - try looking at an app called Soundflower.
2) Once you've loaded the kext and have the new audio device available, select it in preferences as the default output device for system audio.
3) Now you need to alter the audio and pipe it to the real system output. This can be done in an accompanying application that adds callback "IOProc" functions to a) the new device and b) your computer's built-in output device. You can then copy audio buffers from one device to the other, to pipe the audio to your speakers. To increase the volume, multiply all the bytes in the buffer by some factor. See Soundflower's accompanying app.