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Confused with the AC97 structure.....

post #1 of 5
1/13/07 at 2:48am
Thread Starter 
Is it all AC97 based soundcards are not capable of providing analog/digital output lower than 48khz? Is it the lack of individual(hardware) DSP making them unable to support any ASIO/Virtual ASIO driver(including Kernel Streaming),making them no choice but stick to the windows kmixer?
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post #2 of 5
1/13/07 at 7:14pm
They are pretty much hardwired to output DVD compressed music stream via SPDIF (coax and toslink) to a home audio surround system. Interestingly one can find very few computer audio speaker systems that will accept this input. I believe that Klipsch had one for awhile, not sure it is still being made. All the computer speaker systems that are surround seem to be based on the 3 x mini plugs as made popular on the Creative Lab Cards. The XFi itself can be forced to output redbood via its almost hidden SPDIF port.

You can also read all about the electrically noisy computer motherboard and RF inside the computer case as well for reasons that people here do not recommend motherboard based audio systems. I personally think more would use them for our purposes if they output could be configured to redbook (16x44.1) via software. We are not the huddled masses though, we expect better. For a pittance you can get the Chaintech AV710 and get bitperfect SPDIF out. Or consider some of the USB SPDIF sources, like the everpopular MAudio Transit.
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post #3 of 5
1/13/07 at 9:01pm
Kmixer is not at fault, and kmixer is actually capable of supporting just about any sample rate your sound card might support.

What happens is the sound card/chip has a PLL circuit which acts as the internal clock to lock in the sample rate. The AC97 codec requires support for 48 khz. So most of these AC97 sound card/chips would just have one PLL circuit which only runs at 48khz or perhaps multiples thereof (I assume this was chosen due to movie audio being at that sample rate). So it is a complete hardware limitation, and everything must be resampled to match this timing. Of course, they could have included a separate PLL just for 44.1khz, but it would be additional expenses which weren't considered worth it at that point in time.
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post #4 of 5
1/14/07 at 9:36am
Thread Starter 
Quote:
Originally Posted by Bones13 View Post
They are pretty much hardwired to output DVD compressed music stream via SPDIF (coax and toslink) to a home audio surround system. Interestingly one can find very few computer audio speaker systems that will accept this input. I believe that Klipsch had one for awhile, not sure it is still being made. All the computer speaker systems that are surround seem to be based on the 3 x mini plugs as made popular on the Creative Lab Cards. The XFi itself can be forced to output redbood via its almost hidden SPDIF port.

You can also read all about the electrically noisy computer motherboard and RF inside the computer case as well for reasons that people here do not recommend motherboard based audio systems. I personally think more would use them for our purposes if they output could be configured to redbook (16x44.1) via software. We are not the huddled masses though, we expect better. For a pittance you can get the Chaintech AV710 and get bitperfect SPDIF out. Or consider some of the USB SPDIF sources, like the everpopular MAudio Transit.
Do you mean that USB SPDIF devices are supposed to(be able to) provide 44.1khz output?
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post #5 of 5
1/14/07 at 9:56am
You can get 44.1 out of most of the USB offerings. M-Audio USB devices have their own ASIO driver that can configure for 44.1. Edirol is the same way I think. I use 2 different Headroom devices with USB inputs in a bit perfect mode. I happen to use the USB-Audio driver. But ASIO4all is a free alternative. I happen to be currently looking a the USB DACs made by Scott Nixon for my home machine.

Decide your portability factor, and then look for usb based dacs, both by the mainstream marketers, and the smaller shops here. Do some searching of this forum for USB and ASIO and BitPerfect. I think there is a sticky somewhere listing all the USB DACs.
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