Hittade detta på:
http://episteme.arstechnica.com/6/ubb.x?a=tpc&s=50009562&f=8300945231&m=7710992335
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Originally posted by Billy_ca:
Is the sound handled by the CPU or on a seperate sound chip?
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The CPU handles all the sound processing, all the sampling, mixing, and clipping. The only thing that the audio chip in the Mac does is provide the actual signal to drive the speakers. It offers no functions of acceleration or effects processing.
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Otherwise a seperate PCI soundcard could take some of the workload off of the CPU...
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The Windows DirectSound API and Audio Kernel support some features to allow a sound card to use DMA transfers for directly manipulating the operating system's audio buffers to do the requisite sampling, mixing and clipping in hardware. The interface to do that is pretty straight forward when writing a Windows driver for a card that can handle that functionality.
MacOS X's CoreAudio, IOAudioFamily, and AudioUnits API's don't supply a system for accelerating audio handling system wide like that. I've been working on trying to design a way to do this, and thanks to changes in CoreAudio and the AudioUnits API's for MacOS 10.2 the task doesn't seem as impossible as it once did.
However the capability to have a specialized audio processor handle the processing of effects on an audio stream is in place through the AudioUnits API's however it appears that application developers would specifically have to use the AudioUnits which were tied to the piece of audio hardware. Much in the same way that a developer would have to specifically have to develop to OpenAL or EAX. I've not discovered a way to make the system wide acceleration of the CoreAudio system a reality given it's current architecture, but I'm not for a lack of ideas. My main problem is that I don't have a MacOS X driver for my SB Live! to work with as a base, and I'm not sure how progress on that front has been going so I've started to consider putting something basic together myself. Nothing fancy, but just something to make the SB Live! a drop in replacement for the built-in audio. Once I get to that point I can experiment with other things.
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Also, are the sound systems on the iMacs, Powermacs, laptops more or less the same?
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Some different families of Mac's have different audio processors, however given the very limited role that the actual audio chip plays in the system the differences are largely inconsequential and have been for some time.
