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My digital audio equipment

I always wanted to know more about signal processing than I currently do, so I have been eyeing various solution to set myself up with equipment that would allow to get some audio into my PC, and out of it - without busting my budget.

DAC

That was easy, our audio guru Sulo Kallas told me what he is using, and I just did the same - bought myself a Sony MDS-JE520 minidisc deck. That would take care of converting analog input signal to digital form ( and digital to analog, too). All I needed now was a way to get this digital stream into PC. To do that, one needs a soundcard with S/PDIF interface. There are several that provide S/PDIF output (usually coaxial), but very few that have S/PDIF input at affordable price (and reasonable quality).

S/PDIF sound card

After searching the web for a day and going through various reviews and datasheets, I was able to narrow my search to somewhat reasonable alternatives (in other words, exclude everything with words 'professional audio' in the description). After reading some more, I crossed out Creative (resampling everything to 48K), Terratec (Price), Yamaha YMF744 and YMF754 XG cards (resampling everything). What was left is C-media chip which is cheap and does everything I need.

CMI8338 and CMI8738 are C-media produced PCI interface chips that have 44.1KHz S/PDIF I/O capability. They are functionally the same, but 8738 also has modem circuity, which is irrelevant for our cause. As of today, CMI8738 is fairly new, so most of the material on the web deals with 8338 (or it's predcessor, 8330 which is basically 8338 on ISA bus). The material, of course, is very scarce anyway.

The first reference I found was to Audioexcel AV511 card (older version is AV510) . Unfortunately, the C-media chip based audio cards are, as someone put it, 'a bit elusive'. So on I went, to look up if there are repackaged versions of a same thing. There were, and several of them. Excelseries recently merged with Chaintech, and it seems that AV511 is now sold as AV51A by them. Protac sells AV511, and both sell MD-MATE (AV511 bundled with I/O board). Nice as it was, I was not able to find anyone on a web selling them and shipping internationally.

A bit more digging, and it turned out that Leadtek sells CMI8738 based WinFast 4Xsound which includes connector board, too. No luck with online store, tho. My luck finally changed when I found out that Zoltrix Nightingale card is based on 8738 (contrary to what some web sources say), and it is a bit less elusive. Connector board is extra option in this case. Real men will build it themselves, of course. I guess I'm not one of them, because I ordered the board with Nightingale card, it only cost 9 UKP at Makingwavesaudio.

Now getting the card turned out to be the easy part, compared to getting it to work. Make no mistake, you get what you pay for. I started at about 7PM and went to bed at 4:30AM, with analog sound and digital output working, SPDIF input still not functioning (I even put in a clean HDD and installed a clean copy of Win95 on it to see if the problem is in my Windows setup, something left from SB16 drivers perhaps). Appearantly most of my trouble was caused by Plug-And-Pray fu*kup, as always. I removed my SCSI card and NE2000 card to see if the sound card conflicts with any of these. No cookie. I then manually forced IRQ9..11 to be assigned to legacy ISA. No help. In frustration I re-inserted the LAN card to make another data digging trip to net, and all the sudden speakers roared out the mixed starting WAV. I have a feeling that the addition of NE2000 finally brought the BIOS to it's senses, and it realised that the PnP soundblaster is no more. Another possibility is that it somehow conflicts with my QDI TX400 motherboard USB implementation, because I currently have it in non-working state. I don't actually use it anyway, don't even have connectors for USB. However, the BIOS does not offer a way to turn it off, either. I got optical working too, after removing and reinstalling drivers couple of times more.

Continued in a morning and after two more hours of mucking around finally got it to work. For those of you who walk the same path - the optical upgrade that I received did not even resemble tho one pictured on a box. The sheet of paper they call user manual also lists the DIP switches wrong. Working settings for a version that does not have dip switches accessible on a back plate are 1-on, 2-off, 3-on, 4-off. Jumper open. If you try to diagnose SPDIF input and get an error message complaining that the input does not work (this is before the diagnosing is actually done) then the problem lies in DIP switch settings. The board comes with 2-meter optical cable with usual S/PDIF connector in one and and mini-plug in another. Luckily, I had the useless half meter cable which came with minidisc deck, so I was able to scavange a needed connector from there. I the cut miniplug off with half meter piece of cable and placed the right connector on remaining 1.5m piece. I had bought another 1.5m cable from local Sony shop - for a price of Nightingale, optical board, and supplied 2m cable taken together. Damn foolish, but I was sooo eager to try it out.

Drivers, by the way, are a nightmare. The CD-ROM installation goes through OK, asks for Win95 disk to install joystick driver and then just stays there, switching mouse cursor between normal and hourglass. The update available from C-media includes different mixer, so you really want Zoltrix version which is also part of their audio rack application.

Once I got it to behave, it actually works OK, I was able to play MP3 song, record it on my SONY MDS-JE520 deck, then play it back and monitor it via speakers attached to soundcard. Non-windows application support suck, of course. Running Quake shareware version causes instant reboot. MSX emulator that worked fine with my SB16 card anly produces various loud hissing noises.

Here is a nice tip for you -

You don't want Zoltrix or C-Media drivers. What you need for digital audio are Midiman Dio2448 drivers from http://www.midiman.com. These drivers to not implement all the unnecessary crap that C-Media drivers do (like HRTF), just plain S/PDIF input and output, all the needed controls are added to standard windows mixer. If you are using WinME or anything other that accepts VxD technology drivers, then you have to use VxD drivers because otherwise none of your favorite applicaion will work with S/PDIF input (output will work fine). Newer C-Media drivers are totally screwed for digital I/O because all the data gets processed by driver software (easy to observe, volume slider works for digital output, too).

Thanks go to Sulo Kallas for that tip.

 

CMI833X mailing list

For users of low cost PC Soundcards which feature the CMI-8330A ISA & CMI-8338 PCI audio chipset designed by C-Media Inc, used on cards and motherboards manufactured by Protac, Audio Excel, Elite Etc.. Of particular interest is using the cards for 44.1KHz digital audio I/O using a supported S/PDIF Interface. This is the kind of thing you'd use if you ever wanted to connect MiniDisc or DAT to your computer to make digital transfers.

Zoltrix Nightingale

CMI8338

CMI8738

Microphone

I was always under impression that quality microphones are expensive as hell. The reality was a bit friendlier than I guessed. Behringer makes a very nice ECM8000 measurement microphone that sells at $69+VAT (the Estonian dealer robs .about $95, of course). Anyway, that was acceptable for me so I ordered one. They did not have it in stock, of course. So how good is good? Behringer claims frequency range from 15Hz to 20KHz, ultra-linear frequency response. Graph shows something like 2dB away from ideally flat here and there, Sulo says that it actually performs as good as +-1dB over the whole range.

There is one gotcha - the mic is balanced output version, and consumer stuff is unbalanced. So one needs a microphone preamp to convert the mic output to unbalanced signal and provide 'phantom power' for microphone as well.. This time I decided not to be a wussy and build one myself. There are couple of examples on the web:

  • Audio Mixing Console project
  • PAiA Phantom Pre shows schematics for a simple op-amp version. It has two sections, first opamp is used in standard differential amp configuration with fixed gain of 20dB, followed by second stage which is an inverting amp with gain adjustable to 40dB, for up to 20..60dB total. a usual zener limiter is used to protect the first stage op-amp from big voltage transients.
  • Schematic of commercial preamp from Rane Corporation (pay attention to that creative, charge pump phantom power supply!)

You can check out my own version of preamp here.

Video card

What does the video card has to do with audio? If you get glitches in audio every time the image on your monitor changes (or at least most of a time) then it is your video card - or more precisely, video drivers that hog down PCI bus to 'improve' video performance so that the card fares better in video tests performed by magazines. Fortunately, most of manufacturers by now recognize that it is a bad thing to do and most drivers have a way to turn off this behaviour. Some require you to write something to registry (or even INI files), on my old Cirrus 5446 PCI card, upgrading to somewhat newer drivers and moving the accelerator setting slider down two notches was enough. For my purposes the video output is still snappy enough, and my MD deck is now happy even if I surf the web with Netscape Navigator while listening music with WinAmp.

More information on that subject

Software

After I upgraded my PC from P5-200 to CeleronII 600@855, the noise crackling noise came back, and nothing seemed to fix it. I initally suspected the ATI video card, but the noise was even worse with old Cirrus. I also suspected my LAN adapter, but the noise persisted even with LAN adapter and drivers removed. After much of head scratching and suspecting the CMI hardware, I finally bit the bullet and installed motherboard driver updates (which I normally don't - look at the quality of usual driver software!). After several restarts and reinstalling video drivers the Windows was back to normal - and the noise gone.

That, of course is not an end to the story. After upgrading to Windows ME, the pops and cracks were back. You can't install motherboard drivers because the setup says that Windows98 (and ME) have built-in support. So how do you fix it? Change the motherboard!

Stay away from SOYO 6BAIV if you plan to use the C-Media chip based sound card, these two just don't play together!

to be continued as the project advances...

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