Homebrew CMI 8738 drivers Options

[d0gbert]

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:

http://code.google.com/p/cmediadrivers

So long,

dogbert

This post has been edited by d0gbert: Mar 14 2008, 20:30

[DualIP]

I just tried the 0.9.9 driver and like the control panel applet.
One bug I found so far:
Using control panel you can generate test tones to check wiring&speaker setup.
However, both Center and Subwoofer are sent to the same channel of a mini-jack, whereas the other channel of this mini-jack remains silent.
I tested this using two different cards (trust 511 and sweex5.1)

[Dogbert]

I just tried the 0.9.9 driver and like the control panel applet.
One bug I found so far:
Using control panel you can generate test tones to check wiring&speaker setup.
However, both Center and Subwoofer are sent to the same channel of a mini-jack, whereas the other channel of this mini-jack remains silent.
I tested this using two different cards (trust 511 and sweex5.1)

Confirmed and fixed with the freshly released version 1.0.0, thanks.

[DualIP]

found some issues in 1.0.0 :

-in playback mixer, A/V input mute switch seems to be toggled
-in playback mixer, setting microphone slider at it's lowest position doesn't kill mic input fully (as it does with original driver)


moreover, can your driver be used for analog in?
I tried netmeeting audio tuning wizard (XP: start, run, conf...) but didn't manage to get input from mic, CD A/V and line inputs. For some inputs, netmeetings level meter seems to be stuck at max volume.

[Dogbert]

first of all, thanks for doing the cumbersome testing.

-in playback mixer, A/V input mute switch seems to be toggled

By A/V, do you mean the line or the analog/AUX or the CD playback mute switch?

-in playback mixer, setting microphone slider at it's lowest position doesn't kill mic input fully (as it does with original driver)

OK, I have to test this. I suspect that the original drivers toggle the mute switch internally if the volume slider is at its lowest position.

moreover, can your driver be used for analog in?

Yeah, I tried the silly speech recognition thing in Vista the other day, and it worked.

I tried netmeeting audio tuning wizard (XP: start, run, conf...) but didn't manage to get input from mic, CD A/V and line inputs. For some inputs, netmeetings level meter seems to be stuck at max volume.

This might be a netmeeting issue (it's software from msft after all), but I'll take a look at it.

[DualIP]

[quote name='Dogbert' date='Jan 18 2007, 14:17' post='465294']
By A/V, do you mean the line or the analog/AUX or the CD playback mute switch?[/quote]

I discovered this when I hooked up CDROM audio cable to the wrong input and didn't get audio when I maxed & unmuted all.
Indeed I fed the audio to analog/aux/AV input.

[quote]I suspect that the original drivers toggle the mute switch internally if the volume slider is at its lowest position.[/quote]
Or your lowest position doesn't correspond to vol=0 setting.


[quote]
....This might be a netmeeting issue (it's software from msft after all), but I'll take a look at it.
[/quote]
Netmeeting works normally on standard cmedia driver.

I tried the silly speech recognition thing in Vista the other day, and it worked.[/quote]
I'm testing on a pretty clean XP install. You won't find netmeeting in vista...


another question:
Some audio cards come with software ac3 and/or dts encoding. Why isn't this software useable on any card that can passthrough AC3 & DTS (like 8738)?

This post has been edited by DualIP: Jan 18 2007, 17:55

[Dogbert]

I discovered this when I hooked up CDROM audio cable to the wrong input and didn't get audio when I maxed & unmuted all.
Indeed I fed the audio to analog/aux/AV input.

Windows XP plays audio CDs digitally by default with the effect that the analog output of the CDROM stays silent.
The external analog inputs (Mic, LineIn) work here on a freshly installed XP, and the internal inputs aren't much differently handled.

Or your lowest position doesn't correspond to vol=0 setting.

Mhh.. I just tested that and the lowest position does kill the mic fully (to the extend that you can't hear loud input fed to the mic jack).

Netmeeting works normally on standard cmedia driver.

I tested this, too, with the result that netmeeting functions as to be expected.

My XP version is xpsp_sp2_gdr.050301-1519, and I installed it today. All the latest patches and security updates have been applied.

This seems to be a very nasty bug because I can't reproduce it.

I'm testing on a pretty clean XP install. You won't find netmeeting in vista...

sndrec32, the Speech Recognition and all the other Windows applications presumably all use the Win32/WaveMM API, so it shouldn't matter.

another question:
Some audio cards come with software ac3 and/or dts encoding. Why isn't this software useable on any card that can passthrough AC3 & DTS (like 8738)?

You're correct - the encoding ('Dolby Digital Live', 'DTS Live', 'DTS Connect' etc) happens entirely in software, or in the drivers, to be more specific. I suspect that the hardware of these 'premium' cards is identical with the exception of the subsystem identifier and the subsystem vendor identifier and possibly some flags in the internal registers which gets checked by the official drivers. The encoding features get presumably enabled/disabled according to these flags.
NVidia has done similiar things with the GeForce / Quadro series.
So, if you buy one of these cards, you're effectively paying an extra 30$ for a few toggled bits.