Quote:
Originally Posted by FasterThanEver /img/forum/go_quote.gif
> now, if maximum size red font does not convey this to you
> I have no idea how you're going to learn, but hopefully at some point, you do
You are just applying your own definition to the phrase "USB DAC". Using a larger font just makes you a bigger jerk.
Bill
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um, no I'm not, I'm using correct terminology here, and your unwillingness to accept that is not my problem, so Bill, feel like learning something new today?
what we're talking about in this thread is USB Streaming Audio vs USB as a host interface for an audio controller/processor, theres quite a big difference
in a formal "USB DAC" (this term should be stricken from the lexicon, it really should), you've got an interface stage that acts as a slimmed down audio processor, in that it generates S/PDIF digital audio and connects via USB, all of the processing and computation for this is handled by the host computer, using a USB Streaming Audio driver (which is integrated into most every modern OS on the planet, excepting some slimmed server OS variants), the USB interface is not actually acting as an audio transport, nor is it carrying any formally defined audio signal, its carrying digital communication between the host computer and the S/PDIF "generator" (seems a suitable word)
this is identical to what happens on a PCI soundcard generating a S/PDIF output signal, except in that scenario, the S/PDIF "generator" is connected either via I2S to the soundcard's DSP (in the USB Streaming Audio scenario, this is abstracted away and emulated in software, just like USB Print Controllers, the primary computer handles all of the lifting), OR it exists as a directly coupled S/PDIF Tx/Rx on the soundcard's DSP (this implementation specific detail is more or less irrelevant, what matters is that S/PDIF is being "created" (digital to digital conversion) from the serial audio streams generated by the DSP (or emulated software entity powered by the primary computer, instead of hardware offload to a DSP))
This solution, using the software abstraction, cannot handle ASIO, as ASIO is an API which connects drivers directly to software (much like DirectX for 3D applications on Windows, and OpenGL/OpenAL on a larger scale), the original intent of ASIO was to bypass Windows' audio substructure, which is inherently too sluggish for professional mixing (latency is too high, and the internal specifics are too murky for it to be considered suitable as a reference, contrasted to say, Apple's Core Audio solution, which is great right off the factory floor), so like I've said (about 50 times now), using ASIO4All (which is a software package designed to emulate ASIO functionality, its what we'd call a driver wrapper, to continue the DirectX example, similar packages exist to enable 3dfx GLiDE support on Direct3D/OpenGL exclusive accelorators)
My primary issue with ASIO4All and USB Streaming Audio is that we're talking about software emulated low latency access, to a software audio controller, the implementation is far from elegant, and given that the OP stated he didn't own hardware, I suggest going with a proper ASIO supported piece of hardware (which includes ASIO capable drivers)
NOW
you're probably thinking, "but, E-MU 0404 USB, and M-Audio FastTrack, and whatnot, those are all USB, thats a USB DAC, right bob?!"
not quite, those devices are not USB D/A's (and have never been marketed or described as such by their manufacturers, only in the land of internet forums where half the members just parrot one another, has this misnomer come about in full force)
E-MU would describe the 0404 as a "USB Audio Interface", and M-Audio would describe the FastTrack family as the same. Just as there are PCI, IEEE 1394, and PCI Express "audio interfaces", so are there "USB Audio Interfaces", this is quite different than a USB Streaming Audio -> S/PDIF solution, and I'll explain why:
In the USB Streaming Audio solution, you're limited to whatever software can provide, and output only, its a very simple point to point device where a software emulated controller translates between internal data (say your mp3s) which go through a very complex path to reach this S/PDIF converter, now this is somewhat different from I2S <-> S/PDIF conversion, but basically understand that its both a digital to digital conversion, and a protocol conversion (from communication to data stream transfer)
Now in the Audio Interface arena, we're instead looking at a device which offers a microcontroller, its own drivers, and is more or less free-standing hardware, its an add-on to the primary computer's processing abilities, not just its I/O complex (which is a VERY key difference), take the 0404 USB as an example, this is far from a DAC, as it also includes an EMU10k series DSP, ADCs, a complex driver package, and varied analog input and output abilities (such as mic preamps, however opamps don't really deliniate the two), this device not only outputs digital and analog data, it also handles all of the processing associated with it, it decodes and generates digital signals, performs digital to digital translation, and so on, just like a PCI audio interface (such as the E-MU 0404 PCI, or Creative Labs Audigy 2 ZS (which is essentially the same card, as they share the same DSP, all that differs is the analog output stage and driver packages))
this is fundamentally different from your so called "USB DAC", as this device is truly an audio processor, not just a streaming audio converter
oh, and yet another bit of muck that "USB DAC" proposes, is that it requires a headphone amplifier, this is an additional analog output stage, and is not at all required by a proper D/A, all they require is some form of line level driver to bring the output to around 2 Vrms (some do it internally, some use opamps, depends on the designer's intention)
honestly, this is not "my own" definition of the phrase "USB DAC", its the factual data supporting that such a phrase is about as reasonable as "diesel gasoline" or most of the hype associated with HD marketing, in this case, I think you're the one applying your own definition and magical properties to such a mythical beast as the "USB DAC"
if my explanation leaves you curious or needing anything further explained, by all means, feel free to ask for clarification, as I've no doubt theres pieces I lightly touched on, another great suggestion, would be reading FA's digital audio primer:
http://www.head-fi.org/forums/f46/be...primer-410022/
and perhaps take your learning outside of head-fi, Wikipedia has some quite informative and in-depth articles, as well as various sources around the web (even reading literature provided by E-MU, M-Audio, Steinberg, etc would be beneficial)
