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Thinking of switching to digital - understanding PC audio

post #1 of 5
Thread Starter 
Hello

I currently have a system with a discrete X-Fi Elite Pro sound card, and a set of 5.1 speakers being fed by the analogue 3.5mm outputs on the card.

I'm building a new system soon, and will be forced to use another solution for my audio as the current card uses the defunct PCI interface, and will not fit in any current enthusiast class motherboards. I figured that given I will be changing my setup anyway, I may as well look into the possibility of using digital audio outputs, especially having heard about the benefits of having the digital to analogue conversion take place outside of the PC.

However, before I make the move, I am trying to get a better grasp of how PC audio actually works in order to understand what exactly the role of the various parts actually is (and therefore know exactly what it is I should be spending money on).

As I understand it, in the case of analog sound outputs, audio streams in a file on a storage device (whether it's a game's audio files, or a movie rip etc) are in a certain format (MPEG-3, DTS, AC-3, AAC etc). In order to access this, the streams have to be decoded to a format that can be handled by the operating system's API (say, LPCM). The API will then interface with the drivers of the sound card or the on board audio, and this hardware will take the LPCM data and put it through digital to analog converters to produce the outputs on the 3.5mm stereo jacks.

With digital audio, the process is the same except the API will transfer the LPCM data to the sound card, which will transfer this data bit-for-bit to a digital output like TOSLINK or HDMI instead of creating an analogue signal from this data.

I also understand "bit streaming" will pass the audio through the entire process, without being converted to another format or mixed, to the digital outputs, and that for this to happen the software (including the API) and the hardware all has to be able to handle the given format (which may not be the standard LPCM).

Have I understood all of this correctly?

If so, can I ask how exactly is it that conventional sound cards (when using analogue audio) will reduce the processing load on the main CPU in the system? Assuming the sound card is simply converting the raw LPCM data to an analogue signal, rather than manipulating the data to produce various sound effects or mixing, why would using a discrete card improve performance (even if only by a very small margin)? As I understand it, the sound card is doing the same job as the, say, Realtek chip soldered on to the motherboard for onboard audio. The digital data arriving at either the onboard audio chip or the sound card is the same, and all that is left to do is for it to be converted to analogue, so why would one require the CPU to do more work than the other?

Thanks!
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post #2 of 5
Not sure if I can answer your questions exactly but onboard audio still needs the CPU to process the audio as it uses the audio chip to then output the sound. Onboard today hardly tasks a CPU at all. Back in 2000 onboard audio could impact system performance because CPU's only had 1 or 2 threads and the audio was extra processing.

A discrete sound card actually processes all of the audio.
If you use a Optical link then the discrete sound card just outputs the signal and you need a receiver.

So discrete sound cards do process the audio while onboard requires to the CPU to process using the sound chip.
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post #3 of 5
Thread Starter 
I'm just a little lost as to why exactly the discrete card does not require the CPU to process audio, given it seems to be doing the exact same job as the onboard chip.

The main reason I would like to understand exactly what is going on is so I can judge whether using digital audio would make things any different - i.e would you still get a (minor) performance gain when using discrete over onboard audio solutions?

I may be forced to purchase a discrete card anyway, as there seem to be no motherboards with onboard audio that features the HDMI connectivity needed to output 5.1 PCM (TOSLINK as I understand it won't suffice)...
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post #4 of 5
If you just output over toslink as long as it can send the signal you want it doesn't matter if it's onboard or discrete as the receiver then does all the audio work.

I'm not familiar with hdmi for pcm. Is that different from 5.1 channels or Dolby digital signal?

The only hdmi audio I know of is just through the gpu. It's not bad either if your outputting to devices that can connect to it. I've not used it much though.
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post #5 of 5
Uhh... So much outdated info on this thread.

There is no hardware acceleration of audio in the modern operating systems. Only the DSP effects are handled by the soundcard.
So a soundcard doesn't take any of the digital sound processing off from the CPU.

If you still use XP instead of Vista/7/8, then you can forget what I said.
Edited by Tiihokatti - 9/7/14 at 1:25am
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Silent Hawk
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Western Digital Caviar Blue 1Tb Random LG DVD/RW Antec Kühler H2O 620 (with AC F12 push/pull) 3x AC F12 
CoolingOSMonitorKeyboard
1x Glide Stream Windows 7 Samsung S23A700D Logitech G105 
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AudioOther
Beyerdynamic DT-770 Pro 80ohm Xilence Fan Controller 
CPUMotherboardGraphicsRAM
Intel 3570K @4,3GHz Asrock Z77 Extreme4 Gigabyte HD7950 Windforce @1150/1500 2x Corsair Vengeance 4gb 1600mhz 
Hard DriveOptical DriveCoolingCooling
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CoolingCoolingOSMonitor
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