Question for Audiophiles.

[pave_spectre]

Furthering my research into the possibility of a car PC, I am currently examining the options for audio processing/amplification.

Since my chosen motherboard appears to have SPDIF output, my question is, does SPDIF produce noticeably better audio output (ie signal/noise etc) than the analog outputs.

The requirement for a DSP between the SPDIF connector and an amplifier would add another layer of both complexity and cost to my current theorised setup, and I'm interested in a sort of cost/benefit analysis. Cost I can find out but benefit I'm not really sure about, so any info on advantages/disadvantages would be helpful.

Thanks.


---EDIT----

Have just located several amps with digital inputs, but optical, whereas the motherboard would be RCA.


--EDIT 2---
For those interested the more general thread about the carpc is HERE (http://www.pcguide.com/vb/showthread.php?t=42380).

[deddard]

It all depends on how far you want to go - keeping everything digital til the last minute in a noisy environment such as a car is a good idea, and optical is even better.
The limiting factors are the old addage of Garbage in Garbage out. If the amplifier isn't a good quality, shielded unit, and you're not using high-quality, high-efficiency shielded speakers, you're not going to appreciate things.

I'm not a fan of in-car hifi's purely because of the limiting factors - I'd consider them a reasonable sound system, but never stretch to calling them hifi in the way that the manufacturers do.
When you look at the speakers, make sure they are good quality - the car is going to vibrate anyway, and simply cranking up the bass and volume on a low quality set is not the answer.
Another thing to consider with speakers (especially the bass) is how much you can actually get from them - to get the best sound from a system the area it is enclosed in should be as long as it's longest wavelength (in theory anyway!) so sticking really low bass in a car is a waste of space - it just makes the car vibrate - the sound can't propagate properly without smacking into something tinny (the car)
If I were to choose, I'd go for digital as far as possible, with high efficiency speakers.

[Fruss Tray Ted]

'Noticeably' in a vehicle depends on many things. Whereas a laptop connected to a boom box in a truck on a camp road is one thing, a more deluxe setup in a Lexus on a smooth road is another.

Of course the SPDIF is cleaner, but will a difference be heard? I doubt it. It is also dependant upon what powers it. Just how clean is the incoming voltage? In a vehicle, the rectification is not highly refined usually and does vary between vehicles, even of the same make, model, etc. Line noise, road vibration, plug wires, on and on, the variables never cease. RF and white noise,,,

Personally I think a purely DC supply with no alternator sustaining the charge is cleanest, such as when the vehicle's ignition is shut off, or a laptop running off from it's batteries. But shielding may be an issue still, if the 'show' is on the road.

What I question is 'why' a studio level of musical playback is neccessary in said vehicle. Air rushing by your ears if the top is down, the sound of the tires 'peeling' the water from the road in a rain, Doppler effect, etc, all amount to interference and/or sound changes and things that alter what is actually heard by your ears as you travel. Everything around the vehicle affects the sound as well such as reverb in a tunnel or echo in a canyon. Even a quick change in angle on the road where a 'g' force is felt, affects your ears physically as to what they hear.

The main point here is, the system could be flawless, but the environment would be (and usually is) the greater 'equalizer' of systems.

Stepping out of my truck now and into your Lexus,,, :cool: N-i-c-e...

I like your pick of topic BTW. ;)

[pave_spectre]

sticking really low bass in a car is a waste of space
Agree.

Speakers will be good quality, probably Pioneer, Alpine or Clarion, with no subwoofer, since one would take valuable boot space and provide no real benefit, (been in sub fitted cars and didn't find the quality any better than a good pair of 6x9s or 7x10s, just harder to breath :rolleyes: )

The DC-DC supplies I've found specifically for this application claim they handle inputs of anywhere between 6.5 and 30 volts depending on model and outputting constant standard PC voltages. and maitain output even through engine cranking, so noise from that angle should be minimised, but not I suspect, eliminated.

What I question is 'why' a studio level of musical playback is neccessary in said vehicle.

Cause I'm a perfectionist. :p

Don't really need a studio level of quality or I don't think I'd be looking at using mp3/ogg files like I am, but I'd hate to go to the trouble of designing/building something like this, only to have it hissing/whining/popping in my ears on a 2000+Km road trip.

[saphalline]

I still say that SPDIF was only designed because everything these days is going digital. :rolleyes: Audio is and always should be an analog process. But alas, that is not possible on a computer. On the other hand, keep in mind that today's digital audio outputs are limited to 2.1 channels.

Not to mention the source of the music at the computer's end (data files) will be limited in their representation not only by a clean power source, but also by the capabilities of the audio adapter. And if this is going to be based on that VIA mini-ITX mobo, I have to say that the audio adapter will be no better than standard desktop onboard audio. Which is to say that for a "perfectionist" type of concern will be woefully inadequate from the start. No amount of shielding or high-quality speakers will help you with that one. While it's true that most of the time, the speakers are the limiting factor, you haven't heard musical pain until you hear a poor quality audio adapter next to a good audio card.

Think about what you're trying to do and ask yourself how feasible it would be. Not just in terms of a budget, but also in terms of the limiting factors of technology.

[pave_spectre]

If the onboard sound is total rubbish, there is always the option of getting a half decent soundcard like an Audigy or similar at a reasonable price. The downside of that is it then increases the required case size since carpc cases aren't really designed for full expansion cards (think regular car head unit depth). A double-DIN sized case would take one, but then theres another space required for the touch-screen.

That means a regular height case, limiting mounting option, ie no in-dash, or either modding a slimline in-dash or under seat case to accept a full sound card or building a suitable case from scratch. Unless of course I use an external USB soundcard. And I really don't know the pros/cons of those.
As I see it, audio quality has the potential to make or break this project, since that is the reason for having any kind of sound system.


There are lots of possible problems with In-Car PCs, particularly as I am deliberately limiting myself to certain space and cabling distance restrictions, which is why I am researching it extensively before I even have a car to put one in. Even once I have the parts I will spend a lot of time with it on a desk experimenting with different software setups before it even goes anywhere near my vehicle.

At one point I was even semi-seriously considering how well a carpc would fit as one of my purchasing criteria. :D Of course my normal illogic prevailed over my geekly desperation. :p

[pangea33]

pave_spectre, I hope that you care, because about halfway through writing this post I realized that anyone who isn't passionate about audio will just quit reading. In the event you don't care as much as I do, save yourself some trouble and just go with analog outputs. You're virtually guaranteed to have much poorer results with onboard audio than with a separate audio processor. Since you'll be converting mp3s to an analog signal, a built-in mp3 decoder has obvious advantages. I recommend a simple USB audio device since PCI device space is an issue. You can hide it up in the back of your installation space, and won't need to fuss with it after that. Even most competition level audio systems are strictly analog off the back of the head unit. Without taking the rest of these points into consideration, "keeping it digital" won't make any difference. Since you have identified yourself as a perfectionist and an audiophile, I'll be carrying on for a while...


Just because low bass is often associated with knucklehead, license plate rattlers, doesn't mean that a subwoofer is a bad idea, or has no advantage. If you're going for the closest approximation of a true "audiophile" system that a car can offer, there are a number of reasons why you should always choose a separate-component/subwoofer configuration over "typical" oval aftermarket speakers.

First and foremost, round drivers are more accurate than oval drivers. Round speakers have consistant stiffness at all points around their circumference. Consider a two-dimensional, top-down view of the driver. Oval speakers are stiffer around the tighter curve at the end of their long dimension, than in the wider curve at the height of their short dimension. As the magnet drives the voice-coil, varied stiffness of the cone results in varied speed response across the cone. Since physical movement of the cone produces the audible frequency, this necessarily introduces distortion.

Now consider the speaker's shape from a profile view. The distance of the cone from center to long end, is much greater than the distance from center to the short end. This varied distance again impacts cone stiffness, and introduces an entirely different distortion component.

Multi-driver speakers, whether oval or round, have the mid/high range drivers mounted directly over the bass driver. The lower-frequency waves will surround and interfere with the higher frequency waves, adding distortion and coloring the sound. This type of speaker also uses soldered capacitors to cutoff low frequencies as a crossover. In the case of a midrange driver there is no high-cutoff, and the speaker is left to rolloff at the limit of it's capability. Once again, this makes for more distortion. Additionally, cars are built from different materials, and have different dimensions. The crossover frequency of the individual drivers needs to be tuned to the space where it will be used.

The only way to effectively deal with all these variables, is by using multiple round component drivers, and custom crossover points. A mid/tweeter set are often mounted in plates occupying the original oval holes. The individual frequencies should be adjusted by an electronic passive crossover, and then separately amplified by dedicated amplifiers. The biggest "bass" driver that will fit into a typical 6x9 enclosure, is a paltry 5 1/4" speaker. These are physically incapable of producing low enough frequencies, if high-quality audio reproduction is your goal. A low-end range of 60-80hz is about all you can hope for at an acceptably flat frequency curve.

How do you fill this gap? Without cutting holes for 8" subs in your back deck, you'll need a trunk-mounted subwoofer. This works out fine because low frequencies are non-directional and your ears won't be able to tell where they're coming from anyway. With a sufficiently high quality sub, a dual-voice coil model will work well. There are even sub enclosures available which are specifically designed to mount in the spare tire hole of many cars, or into a side panel of SUVs. These leave you with storage capacity that is on par with stock.

If you've read this far, then you probably care as much as I do about sound systems. Run a USB cable from your car's PC to the external audio card, and you've got digital all the way to the trunk. Something most of the professional installers won't even claim. From here you can install a short run of OFC rca cables to an external passive crossover, followed by separate dedicated amplifers. Some companies also make multi-channel amps with electronic crossovers for each output range.

For fairly high quality performance at a lower cost, you can use a decent four channel amp that runs to a passive external crossover, which will drive the component sets at all four corners. It's easy to find pretty good deals on an amplified subwoofer that runs off your amp's line level output. Issues like road noise, can be dealt with through the use of sound deadening material or high sound pressure levels. You can also achieve sufficient sound deading through the use of a big fat Cadillac, Lincoln, or well engineered Japanese or German car. :-)

I think it's apparent that I can go on for days, because you've hit on a subject that I am very passionate about. It would be my pleasure to offer input wherever I can. I think I'm pumped enough to go and rewire my gooseneck EQ now.

[pangea33]

Don't really need a studio level of quality or I don't think I'd be looking at using mp3/ogg files like I am, but I'd hate to go to the trouble of designing/building something like this, only to have it hissing/whining/popping in my ears on a 2000+Km road trip.
If you encode your files from CD, or a lossless audio codec fomat like flac, at the 320kbps limit of the mp3, or the ogg format limit of around 400kbps, you'll be very, very happy. The digital luddites may mock your desire to convert to analog at the last possible moment, but they're missing one very crucial point. Unless you've got a chamber orchesta in the back of your van, you're souce is already the product of a digital conversion process.

Vive la digitale

[jcnoernberg]

Pangea, great post... that's about as "high end" as you're going to get in a vehicle.

[pave_spectre]

This type of speaker also uses soldered capacitors to cutoff low frequencies as a crossover.

ooo yech bleh!!! I've seen (and heard) those, they're horrible.

Multi-driver speakers, whether oval or round, have the mid/high range drivers mounted directly over the bass driver.

Never bothered with that sort of speaker, always go for component splits myself, with tweeters mounted seperately from the main speaker.

The crossover frequency of the individual drivers needs to be tuned to the space where it will be used.
Always wondered how you go about tuning to a mounting space. I have heard of having to tune a sub box during building but since this project will also comprise my first major car audio installation I'm not really familiar with a lot of the processes involved. Prior to this I just picked a decent head unit, speakers and some good cable and voila!. :rolleyes: I think if I applied that process to computers I would be running a HP or Dell.

Just so I don't come across as a complete fruitcake, researching all this without a vehicle, and to hopefully give you some idea about space restrictions and mounting options, all this gear will probably be going into a Subaru Impreza 2.0R, which I will be purchasing in the new year after I get back from leave.

I'm starting to think I may need some help from the GSE blokes at work. :D

More research beckons, but it's off to bed for now. Thanks.

[pangea33]

pave_spectre, can you send me some links from your research? Certainly it's already obvious, but I am really interested in looking into something like this for myself. Are you fabricating something on your own, or are there companies offering a prebuilt pc case that will fit into your dash? I've got double-din's here, and I ain't afraid to use 'em! :-)

"Good" sound is a phenomenally subjective business. The easiest, and most cost-effective method, is to trust the engineer's judgement. They manufacture crossovers well suited to their drivers. More than 90% of speaker companies will provide you with the same passive crossover, whether you're using a 5.25" inch midbass or 6.5". For highs, they both rolloff to the tweeter at the same frequency. This will often work reasonably well, but obviously those mids will have different sonic properties. You might end up with a discernable and annoying spl fluctuation at the nonadjustable crossover point.

One of the biggest problems with 2-way component crossovers is the lack of a true midpass frequency. The mids will receive full signal from the lowest available frequency, up to the crossover point. Anyone who has pumped up the boomin' stock system in their Mom's Yugo, can tell you little speakers don't reproduce bass very well. The crappy sound you're hearing is usually the voice coil maxing out the cone's excursion limits. Distortion equals bad, equals a likelihood of destroying your speaker. Decent amps have built in crossovers, which allow filtering out of the low frequency at a user selected rolloff point.

In order to get the most accurate tuning, you'll need expensive equipment or a trip to your local install shop. They can run a signal across all frequencies, and use a meter to determine where your install requires boosts and cuts. This is where an EQ becomes necessary, but you can run a virtual one in your Car PC.

When selecting your internal speakers, I suggest you take a look at MB Quart and JL Audio. There are many respectable component manufacturers, with quality solutions in most price ranges. We've been talking theory up to this point. If you want to get serious about selecting some specific hardware, the available budget is just as necessary as when choosing computer hardware.

Sorry for blabbering on about this in a computer forum, but it does appear that people want to know. Plus, we're talking about using a computer for the source anyway.

AWD Soobie. Me likey.

[pave_spectre]

MP3Car (http://www.mp3car.com/store/) has the widest range of cases (4) and also has a forum specifically dedicated to this sort of thing where i have obtained a lot of info mostly about frontend software and amplifier options. Not a whole lot of help about specific PC componen
ts though.
I will probably source case, PS, slimline DVD and in-dash touchscreen from MP3Car.

Short-Circuit (http://www.short-circuit.com/index.html) and Mini-Box (http://www.mini-box.com/site/index.html) also have a selection of parts.

The problem with a prebuilt case is the way it limits options, either in where it can be mounted, or in what components it will accomodate.

A custom case is more work but could be built to allow a proper soundcard and still be dash mountable with a little bit of fiddling. I would need assistance from the GSE boys and their tools for that though.

Sorry for blabbering on about this in a computer forum, but it does appear that people want to know.

Keeping one of these threads totally on topic is going to be difficult I think since changing one component in a setup like this will inevitably have follow on effects. I may end up having to moderate my own posts! :eek: :D
And I haven't even got to the advantages/disadvantages and relative power consumptions of 2.5" versus 3.5" sata hard drives. ;)

[pangea33]

I just noticed your other thread entitled "800MHz or 1GHz for Car PC." I guess I was asking about stuff you had already included there, but thanks for the useful links you also posted here.

[pave_spectre]

The reason I seperated the audio question is cause being such a critical element it was likely to take up more time/detail than areas where I am already reasonably familiar and I didn't want it to get lost in a mix of other stuff.

Added a link to the other thread in my first post for reference purposes.

[pave_spectre]

It seems the external Audigy 2 NX (http://www.creative.com/products/product.asp?category=1&subcategory=204&product=9103&nav=1) is a popular soundcard in carPC circles, S/PDIF output is non-functional under Linux though.

Whichever way I look at it, I can't find anyway to fit an internal soundcard and still make it dash-mountable without actually seeing behind the dash on an actual vehicle. And I don't really like the idea of mounting it under the passengers seat, so external may be the way to go, and mount it in the boot next to an amp.

[deddard]

Would it be possible to use something like a 5.25" drive bay sound control adaptor which comes with some soundcards? I know creative do some for their kit, and it may be possible to adapt this sort of thing for use in a car.

[pangea33]

From my limited knowledge, it seems like the problem is space needed for the full-height sound card, that the breakout box connects to. That would be pretty cool for connecting to certain devices, like portable mp3 players and stuff, if there is room.

[pave_spectre]

it seems like the problem is space needed for the full-height sound card, that the breakout box connects to.
Correct.

When you consider than single DIN enclosure is 50mm high, using the Audigy 2 ZS (http://images.creative.com/iss/images/corporate/artwork/art_sbAudigy2ZS_Prod.jpg) as an example, you can see that the card takes up most of the backplane width, estimating from the image around about 90-100mm. getting close to too large even for double-DIN.

Even the Audigy SE (http://images.creative.com/iss/images/corporate/artwork/Audigy_SE_Card_hi.jpg) appears to take up around 60-70mm. Mounting it horizontally using a PCI cable would possibly work, but especially for the ZS, has the potential to block airflow around the CPU, not good even for the low power consumption VIA processors I'm thinking.

A PCI cable could in theory allow an internal soundcard to be mounted externally, but that seems like too much of a bodge for my comfort.