my personal pages

QAS
My recommended list of components for a Quiet Audio System:

Note: this is simply my opinion (as may be slightly out of date since technology changes so quickly).
There is more information about many of the things I mention here at www.silentpcreview.com  Use this site to do some of your own research.

CPU:
Intel Processor P4 2.8 GHz (or higher) with "Hyper-Threading Technology"
Do not get a Celeron processor. AMD64 chips have also done well, with a reliable chipset like nVidia. For quiet systems, you may consider the Pentium M processors. Some motherboards accept them, and there are adaptors for those that don't. Pentium M CPUs may have a lower clock speed, but they are more efficient that P4s, and perform just as well, and are much cooler.

CPU COOLING:
Warning: changing the speed on your CPU fan can cause hardware damage. Do it carefully and always monitor your temperatures!

If your using the fan that came with your CPU, consider a "Zalman fan-mate" to reduce the RPM, and therefore, the noise. Be careful that you don't turn it down too much or your CPU will run too hot! Always use system monitoring software to check the temperature of your CPU. Don't overclock.

A more expensive, but more effective route is to purchase a new CPU fan designed specifically for quiet operation, like Zalman products. ($40-60 range)

Pentium M CPUs can be cooled passively - without a fan (depending on the situation). If you're geting a Pentium M, consider some of the massive heatsink that are fanless.

RAM:
At least 1 Gb RAM minimum. If your motherboard allows, get the 1 Gb on ONE stick - that way you can upgrade easily. @ Gb is recomended, especially for sampling.

MOTHERBOARD:
Get an Intel chipset when using an Intel CPU. I recommend ASUS mother boards. It can save you some cash if you get a board with integrated video card. Integrated sound cards are useless, and if your board has one, fine, but get a dedicated soundcard for your audio work. I don't know why, but people with an Intel CPU, and a good motherboard with an Intel chipset, seem to have far fewer problems and conflicts with professional audio applications. If your using AMD64, go for an nVidia chipset, or do your own research.

VIDEO:
If your chosen motherboard does not have an integrated video card, you will need to buy an AGP video card. You do not need powerful video for music, so a feature-plain 64Mb card from a good company will be fine (ASUS or ATI are nice, stable cards in the $50-70 range). It is important that the video card you choose is "passively cooled" - that is, it does NOT have a fan. Video cards with fans, while more powerful, are VERY noisy. You don't need that extra power for an Audio system.

HARD DRIVE:
For Audio systems, I recomend have two separate hard drives. A smaller one can be used for the OS (C drive) were your Windows and software is installed, and a second large drive (120+Gb) dedicated to audio files and samples. The drive should have at least 8Mb cache, and access times in the 9 Millisecond range or less. You can get even better performance with RAID configurations for your audio drives. However, I don't use RAID, so do your own research.

Hard Drive vibration
As hard drives spin, they transfer vibration to your case which may result in a "hum" and louder seek noises. To avoid this, hard drives should be decoupled from the case. At a minimun, use rubber grommets. Even better, there are commercial products which make it easy like No-vibes ($50) or SunBeam's Harddisk Silencer ($17). You can also do-it-youself: see www.silentpcreview.com for instructions on suspending your hard drive(s) with flexible cord-like material.

SOUNDCARD:
The soundcard is one of the most imortant parts of your system. I recommend professional audio cards with ASIO and GSIF driver support. M-Audio makes great cards in their Audiophile series starting around $100.
Soundblaster Audigy is a fine, cheaper soundcard with soundfont support that can be very handy (use it as a basic sampler). However, if you're doing any multitrack music with effects, I would avoid it. You can have, as I do, two cards.  However, it should be noted that with ASIO drivers, only one card can be used at a time for audio. You can access the synth on other cards.  For example, within Cubase SX, I use my M-Audio card for all audio, but at the same time use the synth on my Soundblaster Audigy card.
There's lots of choice in the "pro" area for soundcards, so do your own research. If using an external card, use Firewire or USB 2.0.

CASE:
Don't over look your computer's case. It can also be a source of noise. I prefer old-fashioned steel, instead of aluminum, because it's weight helps dampen noise (and its cheaper). An excellent case is Antec's "Sonata" which comes with a good, quiet power supply. It's pricey, but well worth it!!

POWER SUPPLY UNIT:
Most generic, cheap power supplies that come "bundled" with the computer's steel case are disasters waiting to happen. Insist on a good quality power supply - a cheap power supply can cause system instability, or worse! (I once lost all my hard drives and data when my cheap power supply blew) Zalman makes nice, VERY quiet PSU's. Other good ones are Enermax, Antec, & Thermaltake.  The PSU included with the "Sonata" case mentioned above is also very good.

Almost all ATX power supplies come with fans. Some are quieter than others. Read about them at silentpcreview.com

FANS:
Your system will have fans to keep the computer cool, but they can be noisy. Try to keep the number of fans low. One will come with your Intel CPU - it's usually not too bad. Another will come inside the power supply. The size and make of the fan will affect how noisy they are. Video card fans are almost always loud, so avoid video cards with fans. Additional  fans that attach to your case may be added, but only if temperature is a problem.

Generally, the larger the fan, the more quiet. Use at least 80mm fans. Zalman fans are quiet and cheap. "Panaflo low" fans are very quiet, too, when used in combination with a Zalman fanmate.

OS
Windows XP. There isn't much choice unless you go to Mac ($!). Linux doesn't have enough professional Audio software available for that platform to make it a viable alternative. I have to admit that I've often been tempted by the Mac platform: there are advantages. However, in my experience using pro audio software, I saw just as many crashes on Mac as I did on my PC.