Hi everyone!

I'm currently working on WDM drivers for soundcards based on the C-Media 8738/8768 chip. I plan to release the entire source code under a BSD-like license sometime in the future. I'm mainly interested in the S/PDIF connectivity because the DAC of the card sucks.

For testing, you need:
- a CMI 8738-MX/8768 based soundcard with S/PDIF (which are available for around 10-15 USD)
- Windows 2000/XP

Some of the features are:
- bitperfect S/PDIF output for 16bit 44.1/48/88.2/96kHz stereo signals through kernel streaming / dsound / waveout
- bitperfect AC3/DTS passthrough
- multi-channel output (that disables the S/PDIF output port unfortunately)
- recording support
- basic mixer support
- UART support (but disabled for now)

Apparently, the C-Media chip supports only 16 bit contrary to the claims in their specs. I haven't been able to get 24bit output even with the official drivers. But 96kHz output seems to work fine on the newer 8738 chips.

You can help me by posting your chip version and configuration, and testing whether 16bit/96kHz and 24bit/48kHz output through kernel streaming works (foobar2000, winamp have the necessary plugins). I'm specifically looking for people who have means to tell a 16bit S/PDIF stream from a 24bit stream.
When the driver loads, it prints the version of your chip to the kernel debugger. You need a running instance of DebugView (http://www.sysinternals.com/Utilities/DebugView.html) to catch the strings. In other words: open DebugView before updating the drivers.

Note that the drivers aren't signed, so you have to install them manually (Update Driver => Install from a list or specific location => Don't search. I will choose the driver to install => Continue anyway).
A 64-bit build has been successfully tested, and I'll probably release a build sometime soon.

Here are the download links for the latest version:


So long,

dogbert

Awesome!

I'll try these drivers out today. I tried some M Audio DIO drivers before which gave bit -perfect wav output as long as you manually selected the right # of bits and frequency, but couldn't automatically change to what was needed when playing DTS or AC3.

The only thing debugview shows is:
[2692] Exiting because c:\windows\system32\runonce.exe is in the Windows directory.
then
[XXXX] Exiting because c:\windows\system32\rundll32.exe is in the Windows directory.

a bunch of times, where XXXX is a 4 digit number.

This is Windows XP Pro, sp2.

My system is a Soltek QBic 3801 with a built-in CMI 8768.

Bit perfect worked great, able to automatically switch to the correct freq unlike the DIO drivers I tried.

My stereo showed 44.1, 48, 96khz all worked great. 88.2 I think also worked but my stereo didn't know what to display when it was playing it, the display got a bit confused.

24-bit also didn't seem to work for me. It would continue to come out 16 bit with directsound selected. With kernel-streaming used in FB2K 24-bit wouldn't do anything at all, nothing would come out.

The major problem for me is that it seems to have disabled all the headphone outputs.

Try this version: http://mitglied.tripod.de/atproc2/CMI-091-release.zip

Works great!

Thanks!

It seems that the volume is now much louder than with the regular drivers, but it's not such a big deal. Just gotta remember to keep the volume slider down. Or it could be I'm just imagining it.

Sorry I can't seem to get the debugging information to get captured properly to give you any further information about my setup.

new release 0.92:
- built with the latest WDK (version 5728)
- first AMD64/EM64T release - this driver should work on your Windows XP x64 installation and on Vista x64. To install the driver on x64 version of Vista, you must disable the driver signature enforcement during boot-up with the F8 key
- stupid fix for a nasty bug which rendered large parts of the mixer useless

I'm keen to know whether the driver actually works on Vista. So if you have a card lying around and some time, please test and report .

Thanks.

When do you think you'll start releasing the source? And when you do, what will be necessary to compile it? I'm interested in taking a look.

released under BSD license, check the site.



You need the Windows Driver Development Kit (WinDDK/WDK, http://www.microsoft.com/whdc/driver/found.../WhichDDK.mspx). I've used build 2600 and 5728 so far.
Unpack the stuff to <DDK>\src[\wdm]\audio, set the paths in paths.bat and you're ready to go. There's a bunch of batch files for building the binaries / updating the driver.

I wonder...how hard would be to modify drivers for 9738 (integrated on many motherboardsl and BTW: http://www.hydrogenaudio.org/forums/index....c=38113&hl= )

The 9738 is a regular AC97 codec, meaning that there are lots of limitations like fixed sample rate (48kHz) etc - a generic AC97 driver should support most of the features of the codec, maybe even bitperfect output for that particular sample rate.
In contrast, the 8738 is a regular and pretty simple PCI codec, so they require completely different drivers and have only very few things in common, namely the C-Media logo on top of the chip .

it sounds awesome! but could I have the following request in the next update:

- software AC3 decode from SPDIF-in

The reason is that I have a XBOX and would like to use the computer as an audio decoder so that I can feed the surround audio into my 5.1 computer speaker setup.

Thank you.

Mhh, no, sorry. I think that's a bad idea because running digital signal processing code in kernel space proves to be difficult due to timing constraints (keyword glitches), and the AC3 stuff is mined with patents. The main motivation behind the driver is to provide a bitperfect transceiver for digital audio signals rather than a DSP.

You could run an AC3 decoder as an application which decodes the S/PDIF In signal to your speakers, but you'd experience a nasty lag (10-20ms and more) due to the limitations of the windows driver model. This particular design flaw has been fixed in Vista, but it requires modifications to the driver and limits it to Vista, of course. I'll probably implement the stuff when Vista is final and I'll have some free time.

Mind if I ask how you got into Windows driver developement? It always struck me as an interesting topic.

thank you d0gbert.
referring to your reply, could you please suggest me which AC3 decoder can do my required work? How can i manage the settings?

Cheers~

Uhm.. more or less by accident. I'm generally interested in the architecture of operating system kernels, and driver development goes along with it.


graphedt.exe in conjunction with a proper AC3 codec. I haven't tested the SPDIF input capabilities yet, so I might try the stuff later on.

Hi there!

Thanks for spending time on a driver for the CMI chip, the native driver really sucks.

Anyway, I have tried the driver both in XP and Vista, and it works well. I had some problems during installation in Vista (BSOD), but I think it relates to uninstalling the old driver (if I just uninstall the old driver I get the same BSOD). Using safe mode I had no problems installing the driver.

The driver works fine but I cannot turn off the digital output. I don't need to, but when the option to do so is present, it should work.

I can't choose multichannel output. I don't need it either, but I can see in the release note that it should be possible, so at least I should be able to.

Is the selection of sample rate on the output automatic and dependent on the input signal? Contrary to the native driver, your driver doesn't have any option to change the sample rate.

Anyway, thanks for a nice driver. Now I am able to get digital out in Vista. Thanks a bunch!

BR,
René

HW config:
Soltek 75FRN2-L
Athlon XP2500+
Terratec 5.1 Fun
Radeon 9600

Hi again,

Just another thing - the mute function doesn't work, at least not for the main volume control.

BR,
René

Yep, that's a bug in the old official cmedia driver - I had the same problem with version 0639 I think.


The analog part of the card is a nice extra, and the main aim of the driver is to provide a bitperfect spdif interface, but...


... u can turn off the digital interface by selecting a multi channel configuration in your "sounds and audio devices" control panel applet (number of channels >=4).
The problem you will run into is that the driver "forgets" the channel configuration after each restart.


Uhm, yes, the sample rate is selected by the kmixer, the way it's supposed to be in every WDM implementation. That means that if you start playing a 48kHz 16bit wave PCM stream and nothing else is pushing stuff through the kmixer, the driver sets the card to 48kHz 16bit. If you start playing another wave stream, let's say 96 kHz 16bit, the kmixer queries the driver whether the stream can be played simultaneously, which isn't possible due to obvious constraints (no support for hardware mixing), so the kmixer downsamples the stream to the format of the current stream, mixes them together and sends the resulting stream to the driver / card.
This is obviously a pretty bad design flaw, and Windows Vista has the ability to somewhere define a default sample rate and resolution. I might add a control application some time in the future though which would implement similiar functionality and some more stuff.


Yeah, and the DAC volume doesn't work on 8768 devices etc etc. There are plenty of hardware revisions out there, and the specifications from C-Media have absolutely no information about the changes and capabilities of each of those revisions.

Actually the DAC volume has been working since 0.9.2. At least it has for me on my 8768.

I should probably be more specific. The DAC slider doesn't do anything but the main volume slider works fine -- and it only changes the volume of the DAC output, since the digital out can't change when it's bit-perfect.

This is fantastic. I have a soyo sy-k7v dragon plus MB with onboard CMI8738 and optical/coax in/out.

I have noticed that my drivers (c-media 5.12.1.639) don't support simultaneous digital in and out.

Do yours?

And.. does the clock of the input need to be synced with the clock of the output in this mode? Or does the chip have an asynchronous PLL for receive clocking?


I will try your version soon,
thanks!


EDIT:
OK, they installed fine, and work! A few issues, though: at first no digital out, only digital in worked. then I was playing an MP3 and changed the 's/pdif 5V signal level' switch (what does that do anyway?) and winamp crashed, and the digital output was brought to life (toslink glowing red). However, since then there is no way to revive the digital input without a reboot. no amount of switching and fiddling worked. Also, there is no way to turn the digital output off.

Also, what is the DAC level slider adjusting, exactly? it doesn't change the wav output volume, but that must go through the DAC, right?

Chip version markings:
CMI8738/PCI-6ch-MX
HRTF 3D Audio
M8Y31-0140
UGG1DB

AFAIK the DAC level slider isn't adjusting anything. See previous posts.

Hello,

I am using an onboard C-Media-Chip CIM8738 with coaxial S/PDIF in and out. AC3 output works fine.

Is it possible record an AC3 stream via S/PDIF-in and decode it ?

OK, all-in-one answer:



In theory, yes. I haven't had the time and motivation to try the SPDIF-in recording stuff yet.


Asynchronous PLL is a few cents more expensive than a synchronous PLL for both SPDIF-in and -out => c-media made the obvious choice.


Digital-in meaning direct loop-through to SPDIF-out ?


The 'official' cmedia driver might have set some registers which need to be unset for my way of handling things.


OK, this is to be expected. I haven't implemented loop-through yet.


It's supposed to do that. It's setting soundblaster register 0x04 which has been marked in the cmedia specs as "Wave Volume".
There's "Wave Volume" slider in the mixer, but that's just adjusting the volume software-wise in the kmixer.

OK, thanks for the reports, I'm currently working on the next version.

So, unless the source data is clock-synced with the 8738, the digital input won't be bit accurate, no matter what driver is used. There will be repeat errors or lost samples, the severity of which determined by the differences in clock accuracy of the source and 8738.



Digital-in meaning I can record from the digital in and monitor it via the DAC on headphones.


That's indeed what seems to have happened (that's why spdif in worked at first, but never again, because the monitoring register was unset)



Thank YOU for your work. I took a glance at the source, but couldn't make heads or tails of it, sorry.

Just tried the 0.94 driver out in both XP and Vista. It works great. In XP I am able to output 96kHz (and 88.2kHz, although my receiver still shows 96kHz - I think it shows the same for both sample rates). I haven't tried 96kHz in Vista.

DTS/DD out works fine in both XP and Vista.

Only quirk I have now is that the volume after resuming from Suspend to RAM is very high. Pressing either the up or down volume just once resets the actual volume to the right volume step.

Keep up the good work!

I've just uploaded a new version (0.9.5) which includes a switch for selecting the secondary SPDIF-in. So recording from SPDIF-in while monitoring through analog-out should work now, but this probably requires turning off SPDIF-out.
You can record stuff now under Vista, and I've re-implemented a small workaround for the XP mixer (sndvol32). The .inf file was broken for 64 bit releases in previous releases, so this has been fixed, too.

René, thanks for the bug report. Power management is one of the few things which haven't been implemented yet - but it's pretty high on my list.

Thanks a bunch. Your the man You have my highest regards. I was going to buy a new soundcard, but because of your driver I don't have to!

BR,
René

Hi, please somebody could help me with SPDIF problem ?
SPDIF output using AC3filter + Nightingale 6 PRO worked properly in XP but in Vista x64 this driver with exactly the same ac3filter version and with the same settings doesn't work. Of course I enabled SPDIF in Sound device settings. When I test SPDIF sound from device settings panel it worked - my receiver switched to DD, but when I play movie it doesn't play in DD.
There are installed two sound devices Speakers and Digital Output interface... which one should be used ? (bsplayer/zoomplayer can set output audio device)... and why there is still some unknown multimedia device even when I installed this driver and this driver can't be installed for this device ?
Thanks you very much.. I appreciate ANY help.

cervicek, the SPDIF interface needs to be set as the default device (right-click the item in the sound applet of the control panel and click the relevant menu item).

the third item probably comes from the stuff which fixes some weird bug of the windows XP mixer, you can ignore it.

Thanks. I'll try it.. and ac3filter must be set to use direct sound or waveout ?

both should work.

If I get a cheap audio card with an 8738, will I be able to do simultaneous digital and analog (stereo) out? Is that a function of the audio chip, the soundcard, or the drivers?

And if so, can you recommend a cheap, reliable card that definitely does this?

Thanks!

yes, but that's limited to 16bit stereo. The DAC of the 8738 models might be limited to a maximum sample rate of 48 kHz though.


it's done in hardware. one signal is streamed through the DAC and the SPDIF interface at the same time. there are some registers to control this, and the drivers set these registers, naturally.



Any sound card with a cmedia 8738 or 8768 chip and spdif in/out will do the job. Pick the cheapest model which has SPDIF connectors.

I just noticed that mixer.exe still runs in the background, and it must have a memory leak or something since I've seen it grow to use over 100 megs of memory. Your drivers don't need mixer.exe, right? It's just left over from my old C-Media installation?

yeah, you can happily delete it.

I'm here again with the same problem... I think I've tried all possible combinations including setting SPDIF as default device and almost all versions of ac3filters with different settings. Now I think the problem is in x64 Vista or in ac3filter because the sound is normally sent to receiver as stereo (or prologic) when SPDIF is switched OFF in ac3filter, but when I switched on SPDIF in ac3filter it seems that ac3filter immediatelly stopped receving/sending sound signal because channel level meters in ac3filter stopped to show any signal.
I also tried to use my onboard Realtek AC97 with SPDIF and the result was exactly the same so I'm convinced the problem is in Vista or ac3filter because when I tried testing sound to SPDIF in device settings it worked fine for both AC97 and C-Media. So the cards and drivers can play ac3, receiver can receive it but it doesn't work with ac3filter :-(
Does somebody have working SPDIF on x64Vista with AC97 or C-Media ? Which drivers ? Which ac3filter ?

It works perfectly fine here with the 32bit version of vista and media player classic which uses its internal filters for AC3 passthrough.
The driver might have failed to install - the x64 version of vista doesn't allow unsigned drivers, and since I'm not able to sign the drivers by myself or cash out ~500 usd to msft, you will need to disable this policy by pressing F8 each time you boot and selecting the relevant item in the menu.

You're right. I reinstalled Vista to 32bit and with Windows Media Player Classic it works when AC3 filter is not used.. and it doesn't work in x64 in ANY configuration. So the problem is in ac3filter and somewhere in 64bit :-)
Unfortunately I have to use 32bit Vista... but better then Pro Logic :-)
thanks

New release: 0.96.
This release brings mainly improvements and features for Vista, mainly the implementation of WaveRT (support for very low latency recording/playback, that's probably gonna replace ASIO sooner or later) and support for SysFX:


The current release might be a bit unstable.

First of all, big thanks, really great driver, you saved me!!
I'm using it successfully with a Nightingale card and Vista.
The only thing that didn't work was the output of dts .wav files.
In my spdif properties, there is only 48 kHz, and it says that this
is the only frequency my digital receiver can handle.
But this is definitely not true, I had a C-Port soundcard before,
and it played these wav-files, and my receiver ate them with a spoon.
So is there anything I can tweak or do to enable 44.1 kHz output?
Thanks in advance for any hints!

There are two ways:
1. Use non-WaveRT drivers and a kernel streaming outplug plugin. (foo_out_ks.dll for foobar, out_ks for winamp).
2. Use WaveRT drivers and an output plugin which employs "exclusive access" to the soundcard. The exclusive access mode of the vista sound system bypasses all the mixing by design and passes the stream directly onto the soundcard. If I recall correctly, this is just an extra flag for opening a sound device through WaveOut, so the implementation should be fairly easy, but I haven't seen any support for that in output plugins. But I guess it's just a matter of weeks before this gets implemented.

Good luck,

dogbert

Do you use your Nightingale in Vista x86 or x64 ? Does the SPDIF work in ac3filter ? I have the same card but couldn't get it work in x64 + ac3filter.

I use it in Vista x86, and ac3 works perfectly with ac3filter.
@dogbert:
What does "The current release might be a bit unstable." mean,
is it the 0.95, that is unstable or the 0.96?

I feared that 0.96 might be unstable because
1. a lot of new stuff has been implemented, mainly WaveRT
2. I don't have any other machines for testing, and the problem is that I disabled stuff like kernel paging for debugging purposes which would be enabled on normal machines. Thus, I might miss a few bugs which might occur on normal machines.

But I haven't got any crash reports in my inbox, and it's working on my machine without a single crash for the last few days, so I consider it to be reasonably stable now.

Thanks for your answer!
Method one would mean not to take your drivers, since they are (now) WaveRT, is that right?
And method 2..."it's just a matter of weeks before this gets implemented" - do you mean by you?

I provide both WaveRT (x86-WaveRT.zip) and non Wave-RT (x86.zip) drivers, so you can choose.


Uhm.. I'd do it if the output plugins of winamp/foobar were open source. But they aren't, so we have to wait for the authors to implement it.

First, a really big thank you for programming this driver!

Has anyone been able to get 24bit output before I rush out and buy a cheap generic 8768 card (sweex 7.1)?

The datasheet clearly mentions that the chip should be capable to do this:

http://www.cmedia.com.tw/files/doc/PCI/CMI...20Rev%201.0.pdf

The 8738 datasheet only mentions 16bits.