Audio
Linux Audio Support
In the last year many audio chip's embedded on the motherboard have had driver work completed under Linux. Although some do not work, most do, and this includes the high end AC3 output on them. As for Audiophile PCI cards, support still remains poor, but some cards are supported.
Alsa or kernel module
I always try kernel modules first, then ALSA. But in kernels 2.6.x and newer, the base portion of Alsa is what the kernel uses. If your installation does not boot with sound support working, grab ALSA and let it auto detect your sound card then set up the configuration. ALSA also has a few nice extra features over what stand alone kernel modules may offer, but if you are only outputing AC3/DD/DTS then you don't need them.
What do you really need a sound card to do? What do I need to for TV, DVD's, HDTV, CD's?
If you don't have a seperate audio receiver for your HTPC, any sound card will work. If you have an external audio receiver (That does analog, DD, DTS, etc decoding) not much is really the answer. Hardware is actually easier and cheaper to build for soundcard/motherboard makers to output digital to another device since it is just redirecting data and never processing it.
If you are using an older audio receiver that only takes analog/stereo inputs then you just need a 3.5mm mini stereo plug to 2 rca plugs Y cable ($10 from RadioShack). Just plug the 3.5mm plug into the line-out or speaker-out jacks on the soundcard and the 2 rca plugs connectors into your receiver and you're done. If you use the line-out you will have to use just your receiver to change the volume. If you use speaker-out, your computer can also control the sound volume but so can your receiver. This second way is usually not a good idea since if your computer volume is turned very low and the receiver high and you accidently raise the volume on the computer real quick the change is drastic and you are more likely to damage your speakers from high volume accidents. You are also more likely to get humming in your audio when going the second route. I have used both for some time but not in never in a HTPC. Having more than 1 way to control volume in a HTPC is a pain.
If your going Digital for audio out you have a little more to understand. The 3 most popular digital digital audio formats are DD, DTS, and PCM. DD and DTS are compressed audio formats, like Ogg and mp3. PCM stands for Pulse Code Modulation and is not compressed (Such as a CD). DD and DTS do not better audio quality alone, but when you compress audio you can store more of it in a smaller space and therefor you can increase the quality (or amount of data) of the sound and still fit it into the same space/disk area as non-compressed audio. This is why we see DD and DTS on DVD's.
Most everyone has heard of the company DTS (Digital Theater Systems) and Dolby Labs (their product is Dolby Digital). People almost fight to get tickets to new blockbuster movies in theaters with these sound systems when sound quality will be important (Remembers Star Wars Episode I? It was only allowed to be shown in DTS theaters, only about 15% of theaters had it). Another popular sound system is Sony's SDDS technology. The differences between DTS, DD, and SDDS are the bitrate, sampling rate, and compression of the audio.
The higher the bitrate and samplerate but the lower quality loss in compression, the better the audio quality. All of these audio formats are very close in quality, however, DTS usually provides the best sound quality as they do not compress the digital sound as much -- meaning that when they encode the digital stream, not as much sound data is lost (Take an mp3 for example, the sample rate is 44.1kHz (How many times per second the sound is sampled/checked) and the bit rate is 512Kb/s (the amount of pure digital 0,1's of data being read per second). When encoding a CD to an mp3, your sample rate stays the same, but you drop the bitrate to 192Kb/s or 128Kb/s, meaning you're trying to shrink the amount of data allowed to store a sound file by using compression that will drop some sound quality in order to make the sound file smaller file but hopefully keep as much of the original data as possible.)
The difference between DTS, DD and SDDS what sample rate and bitrate they use, and also the maximum number of unique speakers they support. Such as 5.1, 6.1, or 7.1 If you have a Digital home theater, your receiver most likely supports DD and DTS. There are ones that support SDDS but it's almost never used for consumer electronics. There are also even fewer number of DVD's that have SDDS audio tracks. DD and DTS are the most common and all that most people will want to have. For any type of stream, regardless of DD, DTS, 5.1, 6.1, 7.1, type of receivers, etc. it does not matter on the computer which one you are using -- The computer doesn't do anything but send the data off to somewhere else. You just need to make sure that whichever audio track you select to use on your DVD, that your audio receiver supports it. All the data streams are just sent out your audio card to your receiver without caring what type of stream it is. A $23 sound card with SPdif output can do everything, and any future formats that come out because all the audio data is sent "as is" to the receiver for processing. (Note: If your receiver supports only DD and you try to play a DTS track, your reciever will either be silent or play static.
S/Pdif (Sony/Philips Digital Interface) is the standard that is used to send a DD, DTS, and PCM streams from one device to another. There are two types of S/Pdif interfaces. Coaxial and fiber. There is a long running debate over which is better. They both send a pure digital signal, rarely if ever will you loose a 1 or 0 of data. The only difference really is regarding timing. A digital stream is time sensitive. The more "stable" your timing is of your 1's and 0's the better quality of sound you will have. The debate over which is better, fiber because it uses light which is more stable, but it also has to be changed from electricty to light in the computer and then back to electricity at the audio receiver, vs coaxial that is more easily effected by RF and other atomic particles. Most experts I've talked with do side on coaxial. They are both good and I recommend whichever is easier for you to setup. Basically some coaxial sound cards are better than some fiber, and the other way around. Unless you want to research light<->electricity on each card you may buy, have access to how the cards were made, and care enough, just pick whichever is most convenient for you. The coaxial input on my receiver was being used by a DVD player so I bought a sound card with optical SPdif out. That's how I picked. Coaxial is easier to deal with also, since you can sometimes break fiber. Also, you do need a 5.1, 6.1, or 7.1 AV Receiver that supports DD and/or DTS. If your motherboard has coaxial and the chipset is supported under Linux then there's your answer. Optical sound cards are a little harder to find than coaxial too.
Last, "6 channel audio support" listed on a sound card or motherboard box does not mean it has SPdif. What "6 channel audio support" usually means is it has three 3.5mm stereo jacks that when using the right software it will treat the line-out, mic-in as center and sub. If you have 3 sets of regular computer speakers you could get 5.1 audio, but you cannot connect three 3.5mm jacks to a single SPdif input on a receiver. Look for something that says it has a SPdif audio jack.
Audiophile cards
Right now, the only audiophile card that is reported to work is the M-Audio 2624 card. This card is running $100+ (US$) currently. It has TOSLINK optical out, low signal to noise ratio, and also includes 6 individual analog outputs for supporting "future audio" configurations.
High End Sound Cards
The next choice are the Sound blaster brand. The Audigy2 and Extigy can support DVD-Audio 192kbit audio (if you are using normal computer speakers), which is the next generation "CD/DVD", TOSLINK optical and coaxial S/Pdif out, firewire, and a remote. If you're willing to dish out the nearly $150 for one of these to get that little bit of extra sound, go ahead, but without high end speakers, you won't notice anything different.
All you really need is a S/Pdif interface anyway, why get things you won't use?
Good point. That's why I chose this option myself. I Google'd for "sound card Alsa 8738". The results turned up 2 cards, the Nightingale and the AudioExcel "TheaterExcel" (The AudioExcel card is also branded as the Chaintech 6 Channel Sound Card Model AV515M). Both are about 3 years old. Since everyone was sold out of the Nightingale cards, I bought the Audiotech card from newegg.com for $23.00 including shipping. 3 days later I dropped the card into my system, ran alsaconf to configure it, followed the "Enabling S/Pdif" notes under ALSA's sound card matrix listing for the 8738 chipset, and sound was done. In less than 5 minutes (including boot time) I was listening to 5.1 DTS sound on my AV Receiver. (If you use Mythtv, Mplayer, or Xine, see their README's and FAQs about enabling S/Pdif (5.1 sound)
*Note: I spent over 20 hours researching to find which chipset is supported and that have TOSLINK output. The only cards I have found that do are the ones mentioned above. If anyone finds more cards that work, let me know so I can include them here.
*Note: Fiber cable isn't cheap. It runs anywhere from $2-$5 a foot. When I purchased my sound card, I was lucky because it came with a 5 foot cable, which is all the length I needed. If you have to run a long length of fiber it could be expensive. I did get some gigabit Ethernet fiber to test as it is cheaper if you find a good deal, but it does not work with AV equipment, it's designed for different light frequencies. There also is not much difference in quality, even when comparing fiber material (plastic or glass). Glass will go further than plastic since it's more pure, but plastic is just fine for any 10foot length or less. If you have to get audio fiber, look around for a bit first. As for Monster Cable, I believe it's over priced and not worth the extra money. They do shield very well and make sure braids are audio time corrected for difference frequencies, but that makes a small difference. If your speanding over $2000 on speakers then you may want to get Monster, if not, find speaker wire that looks like it has the same braids and shielding and you'll be well off. I have to say, I laughed when I saw $50.00 gold plated connectors on USB cables that Monster sells. Gold plated is good if you plan on leaving something for 10+ years, but who leaves a USB device where it can corrode and you can't unplug and plug it back it to scuff up the touching points for a perfect connection again? My point is many people are selling things you don't need, when you don't know you don't need it.
Quick notes on receivers/speakers
The AV receiver is the hardware that powers your speakers and does the DD/DTS decoding. The AV receiver is not considered part of the HTPC. To decide which receiver to get you'll have to read reviews on different receivers and speakers. More wattage isn't always the most important thing. High wattage is ONLY needed for your bass speaker (Most high-end satellite/midrange/tweeter speakers use less than 50Watts) and your bass speaker will probably have it's own amplifier built into it. Quality (SNR [signal to noise ratio]) is more important than how loud your system can be. I have never turned my system up past 60% due to worrying about cracking walls, it runs at 43% for movies, and that is loud. A system with 500+ Watts is going to be plenty for most people. If you are building an expensive and large enough home theater that needs more than a 500 watt receiver then you will be doing your own research or having someone do this for you.
Find out what frequency ranges you like to stand out. No two people will probably compeltely agree on which receiver or speakers sound better. I prefer sharp highs and hard hitting lows, a bit like what 70% of "complete" audio systems are made to fit. If you like good mids, then a Bose system is right up your alley. Most audio manufacturers don't have much quality difference between lines for receivers, unless there is a definite quality line difference. Speakers are completely different though.
Food for though... An interesting research project was done to compare lower quality audio with higher quality video to higher quality audio to lower quality video. The result was that the setup with higher quality audio actually had people rate the lower video quality better than the setup that had the better video quality. Reasons included that the mind does use audio to help build a mental picture of what it sees. Sharp crisp audio can make you think you're seeing things in more detail.
Wattage is important in bass sound, but not always. Extremely large subwoofers result in non-crisp bass because it has to move more cone mass and can not vibrate as fast, unless it has a lot of Wattage. 8-10 inch subwoofers with a good amount of wattage and are the most popular. If you want the floor shaking bass you should add into addition, not replace, a good small subwooder. My 7 inch 120Watt bass speaker is more than enough to shake things more than I need. It does lack a lower frequency response that larger (10 inch) bass speakers can give for the ultra low rummble. Most people will be happy with 1 sub, even in a high end home theater. Only if you are an audiophile and want every type of low frequency sound to shake will you want to look into a more full system. Also, speaker box design can be very important. My 7 inch 120Watt sub can hit harder than many 200Watt subs because of the sound box/echo chamber that was very well designed for it. Also to make bass better, stick the speaker in a corner of the room and it will give you much more of a stronger sound -- Acoustics is quite incredible when you have it just right as you can do more with it than with power alone.
A good mid and high frequency range for a center speaker is important as it's the only speaker voice comes out from. If it's too much high, or low, voices will all be in that range. You can slightly notice higher female voices having higher harmonic pitches drop out, if you know what to listen for. Lacking bass in a center speaker is not as bad if your bass speaker is near the front/center of the room. Bass is not as direction and the ears can't pick up on where low frequency audio comes from as easily. (Often why there's only 1 bass speaker). Most stereo systems will take bass normally sent to all speakers and redirect it only to the bass speaker.
The same frequency concerns for the side and rear speakers exist as for the center speaker. So basically make sure you have good mid and high's on all speakers.
A quick audio improvement is to replace the speaker wire that may come with your audio system. (Rarely do they come with it) The reason is that most wire that comes with it for free is cheap. It is usually low quality 18 guage wire. 12-14 gauage is what you need for mid to high frequency and 10-12 for low frequency. As for monster speaker wire, if you spent over $1k on your speakers, you may consider it. If not, don't waste your money. Goto radio shack, lowers, home depot, walmart, Best Buy, or anywhere they sell speaker wire. I bought 100 ft of 12 guage "mid quality" for $30 from Best Buy. For my bass speaker, I bought some high quality RCA 75 ohm stereo cables frmo Radio shack. 20 ft for $30 for my Subwoofer.
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