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Originally Posted by Currawong /img/forum/go_quote.gif
You could look at this way for simplicity: A sound card is something that acts as a digital to analogue converter. It can be in your computer or not.
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a sound card is not synonymous with a digital to analogue converter, a digital to analogue converter is a part found on a sound card, however the sound card will also have DSPs, ADC (or a CODEC, in place of separate DAC/ADC components), and on newer soundcards, DRAM, theres also some very complex software that goes into a soundcard, compared to something as simple as a PCM DAC
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The confusion probably comes when you have sound cards which have digital output (so they aren't converting anything except the connection) and DAC/amp combos which are amplifiers with a DAC (sound card) built in. |
actually the sound card/DSP is still handling format conversion and decompression/compression, consider Dolby Digital Live output, the DSP is still taking the 5.1 from the "ether" of software, and putting it into a format that a D/A using an AC-3 decoder can actually make sense of, theres still quite a bit going on using digital output, the only thing you're NOT doing, is using the built-in D/A and opamps
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I think the naming confusion comes as for a long time, PCs didn't come with sound cards by default, or required them to be an add-on card. Also most PC motherboards only have fairly basic audio built in. If you want digital output (or audio that wasn't crap) you have to buy a dedicated sound card. Some people just bought something that does the same job, but is in an external box connected via USB. Thus people tend to call boxes such as the M-Audio Transit or EMU0404 (which plug in via USB) an "external sound card". Since it's not a card at all, but a box, I tend to call them external audio interfaces. |
most modern ATX/BTX derived PC motherboards have some pretty complex audio circuitry built in, almost all ATX and all BTX derived boards will offer at least 6ch audio from a media controller on the southbridge, and at minimum a 6 out/2 in CODEC, more complex solutions have gone as far as integrating Envy24 or EMU10k into the board, and providing discrete multi-ch DACs and stereo ADCs, keeping the entire lot above 100 dB SNR, and that kind of solution is starting to be seen more and more in the enthusiast segment
as far as USB streaming audio is concerned, it depends on what the device actually does, USB DACs and amps require pre-processing done by the computer, using the CPU, as they can only accept the rough equivalent of LPCM input via USB (this is all handled by the host operating system in real time, although its very inefficient for 3D audio, compared to using a discrete DSP (as the CPU is a general purpose processor, it can handle audio processing, which is generally very repetitive, an area where DSPs (anything from VIA's Envy24 to nVidia's GT200) excel greatly)
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This confusion doesn't exist in Macs. It's just "inbuilt audio" or "external audio interface" for us. That all Macs have Firewire (except the new MacBook) and optical out makes things more flexible too. |
just because you call it a mac doesn't mean it doesn't have to obey the same rules as PC hardware, as its all the same componentry (even the Motorola based boxes, plain and simple), what I mean here is, the same exact things are going on the background, even if you don't ever see them, yes, the hardware offers you FireWire and optical S/PDIF, that doesn't make the platform any different, as these are merely additional features, they also don't make it any easier or harder to understand (well, if you let the Apple store shop for you, its easier
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Maybe the solution is to look at any device according to its functionality and where the digital signal is converted to analogue. |
perhaps, but if this is your solution, why are you calling an orange an apple and a pear a strawberry?
now, to honestly answer the OP's questions:
you will require a DAC regardless of what solution you go with, and it always exists, a sound card, or "external audio device", will have the DAC alongside DSPs and various other components (as mentioned above), a discrete external DAC (here, if you want me to name things by what they do) will accept an LPCM signal in, be it from USB streaming audio, TOSLINK S/PDIF, or coaxial S/PDIF, which has to be provided from a digital output source (we could say transport, but a rose by any other name...), meaning your sound card or "external audio device" (whatever you chose)
as far as sound cards go, all personal computers ultimately have one, it may be in-built (such as the MacBook Pro digital and analog outputs, these are all provided via a CODEC (afaik, as it would keep costs, power consumption, and footprint down, which would be the largest concerns for a notebook, in that order) which is connected to the Intel ICH that also controls your disk drives, and some other components)
however you end up connecting your system, you'll basically come down to having an analog output, which will then be fed into your amplifiers
5.1 is no different, its just a more complex DSP to handle it, a more complex CODEC or DAC (or multiple less complex DACs), and some pretty good compression schemes (AC-3 and DTS as opposed to mp3 and ogg vorbis, stuff like that)
to get 5.1, the optical output MAY support this (I honestly don't know, or feel like finding out), however if it doesn't, you would need an "external audio device" which is capable of 5.1 or 7.1 output, this won't be a straight DAC mind you, this will be a processor, such as the M-Audio FireWire 410, or Creative's USB based X-Fi (which, afaik, is not Mac compatable)
hope this helps explain the reality of computer audio, and if you've got any more questions, feel free to lemme know
cheers