Computer Audio, Pt 1

[fussnfeathers]

I figured I'd do this in stages, rather than all at once, and just expand it as needed.........since there's no "edit post" function........ :)

I'll start by giving a quick explanation of the three types of computer audio, onboard, inboard, and outboard.

Onboard sound has been around for years, even before Creative. In fact, the old systems you still see in use in offices, somtimes, have Creative SB16 chips built in. These days, onboard sound is much better, with both the nForce chipsets and Intel's new HD chip. For the average user, this is just fine, but it has some drawbacks, soundwise, and particularly nasty ones for somebody looking to do home recording. One is noise. Since the chip is located directly on the board, it's on the same plane as the power signals, and in many cases, placed very close to power carrying traces. Since electricity has a sound, and motherboard traces generally aren't shielded very well, that noise introduces itself to the audio stream. This can be either a low hum (the dreaded 60 cycle hum.........the frequency of electricity), or thumps, hisses, crackling, or other sorts of nastiness. For the casual listener, this is generally unnoticable, as the volume level is kept low, and when listening to MP3 audio, is usually hidden in the already rather noisy audio track.

The other big issue, for pro audio guys and gamers, is latency. Since onboard audio is either totally or partially host-based, the CPU is doing some of the work to produce the audio. Even in chips like the nForce, the CPU is being tapped. There's a chip there to decode Dolby surround, but it's still not true hardware rendering from start to finish. For gamers, this can result in an FPS drop, which is pretty unnaceptable.

Neither of these issues will completely go away, no matter how good the onboard chips get.

The second, and most common today, is inboard audio, such as the Audigy 2 or Revolution cards. These cards remove the signal processing from the motherboard, and use dedicated chips, powered by the PCI bus. By removing the chips from the motherboard, and putting them on their own card, much of the noise is reduced, but not all. A noisy TV tuner card, a RAID controller, or a network card can re-introduce noise into the signal. The main reason for this, again, is host-based power. For example, if you have an older modem, and fire it up because your broadband went down for some reason, you'll likely hear pops and beeps, very faintly, from your speakers. In effect, the modem is sharing the PCI signal with your video card, using the same traces, going to the same place on the Southbridge chip.

Latency is also still an issue, but not as bad. Switching to an Audigy2 card from onboard sound will boost your FPS in games by 10% or better, due to the better transfer rate of the PCI bus. However, since current PCI bus transfer rate is limited to 200mb/s, some latency is still there. Again, for home recording, this is a major drawback. ANY latency while trying to record yourself live is a major headache. Inboard cards like the Audigy also lack true 24 bit performance, as most will use power-saving chips in the 18-bit range, while adding two 24 bit chips for surround capability. Note, that this is NOT TRUE in all cases.......the Revolution uses 24 bit chips throughout the pipeline, but the sensitivity of the chips also draws more power, and due to that, the decoding is host-based.....meaning the Revolution still uses the CPU to do the actual decoding. The Audigy removes the CPU from the equasion, but uses 18 bit chips for the majority of the decoding process. While decreasing latency, it also decreases the sound a bit.

For the casual listener, the difference is minimal.

Outboard sound is still the ideal solution, in that it not only removes the processing chips from the motherboard, but it also removes the power supply from the motherboard. In this way, outboard sound modules are able to use true 24 bit chips, with little to no noise, and very low latency. Higher powered 24/196 chips simply cannot be used on a PCI based card, but can easily be used in a self-powered box. In addition, any power and signal related noise can be easily removed by using readlily available RFI/EMI shielded cabling, high quality UPS supplies, and by simply moving a cable. Latency is also low, due to the total processing chain being removed from the machine, as well as the higher transfer rates for the USB or FireWire chains. FireWire B, for example, is an 800mb/s transfer rate, or four times that of the PCI bus. Since that signal goes directly to the Southbridge, bypassing both the CPU related processing, AND the PCI bus, latency is negligible.

For the gamers, I did a test, using my onboard AC97, an older Audigy Gamer, and an M-Audio FireWire 1814. All tests were done in two-channel, since the 1814 doesn't support surround sound on its own. I also used M-Audio Studiophile LX4 monitors, with two two-way sats and a sub (4" midrange, 1" Mylar tweeter, 8" sub, low but very very clean power)

Using a scope, my ears and eyes, and Star Wars Galaxies' FPS and ping monitor:

Onboard sound: 10fps/avg, lowest frequency 45hz, highest frequency 10khz
Audigy Gamer: 19fps/avg, lowest frequency 41hz, highest frequency 10khz
FireWire 1814: 32fps/avg, lowest frequency 35hz, highest frequency 12khz

Besides the obvious gain in FPS, the sound seperation increased as well, at approximately the same rate. With the onboard, the game sounded fine, but "close". With the FireWire, the sound seemed to fill the room.

All tests were done using a Radeon 9600XT, a P4 2.4C ghz, 1 gig Kingston ram, and no overclocking. Stock speeds on all, to reduce any frequency distortion due to excess heat.

I'll have the next section up probably tomorrow, which will explain more, and get into sound recording and mixing a bit. Stay tuned............
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Big enough to scare you

[Google]

[Hoedizzy]

Interesting, didn't know that the onboard effected the fps that much.

[smith.p.sean]

damn... blink... blink........... blink. I suggest stickyage!!

Man, so perhaps i should look into getting a soundcard then...

[Josh]

[Ham_fisT]

Nice Work FnF

Stickage???
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Yeah....... ok