I personally feel that arguments concerning PC versus Mac may have had some merit in the past as computers were being developed, but today it's pretty much a meaningless debate, IMHO. Chose whichever computer you prefer, either one will be able to handle music just as well as the other one.
I personally own a PC and have no complaints. In fact, I use a notebook which is nice and portable, which brings me to my next point.
Don't look to a computer for sound
I mean, you can if you want. But personally I think you'd be far better off looking into getting a small mixer interface, and external amplifies. Then your sound quality really has very little to do with the computer at all.
Just to give you an idea and some food for thought I'll describe my "sound equipment". I'm not necessarily recommending these precise products, but I'll point to them just for reference.
To begin with I have a very simple Compaq Persario notebook computer. It's the cheapest model I could buy. I think it was about $258. I bought it at Wal-mart. It works fine.
Then for the sound system I bought the following (again just suggestions and not recommendations)
For interface to the computer I got a Behringer 1204 mixer.
Behringer 1204 USB
Wow! That went up in price since I bought mine. I think I only paid $125 for mine.
Anyway, that's just an idea. They also make smaller models.
Other companies make mixers too. Just be sure that whatever mixer you buy has a USB connection to the computer and a 48 volt phantom power supply if you're planning on using condenser studio mics.
This mixer has both.
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For input into the computer you'll need a microphone. I bought the following condenser mic and I'm very pleased with it:
C-1 Studio Microphone
I actually bought two of these along with stands for stereo input. They also require cables which are about $10 each.
Yep, it cost to build a sound studio. But this is about as inexpensive as it gets really. These are fantastic mics for the price. They perform as well as mics that cost well over $100 a piece. I'm totally pleased with these mics. And they plug right into the 1204 mixer which supplies the 48 volts phantom power they need.
Then the mixer plugs right into the USB port of the computer, so your ALMOST done. This get's your music into the computer. You also have left over of channels for other inputs, and trust me they tend to come in handy. Especially if you ever find yourself wanting to record with other people and additional instruments. Someone can plug their guitar, bass guitar, keyboard, or what have you, right into the mixer and off you go. You also have standard stereo inputs for imputing music from stereo devices and/or backing tracks.
Music Output
So far you've got music into the computer. If you want the computer to play the music out this audio system you'll need either headphones (which plug right into the mixer and are great to have when playing with backing tracks, or a click track). Or you can put the output of the mixer into some sort of stereo amplifier.
I personally just use a guitar amp for the output and play it in mono. I just plug the headphone-out jack right into the guitar amp and I've got all the volume I could ever want + reverb too if I want it.
My amp is just a 25 Watt Fender Frontman that sells for about $99. Of course I use it for the guitar too. ;}
But anyway, that's my story.
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Like I say, this has all just been offered as food for thought. I'm not necessarily recommending any of these specific products. I have nothing to really compare them with. All I can tell you is that I'm happy with them and they work for me. And ultimately they were about the least expensive system I could put together, yet the quality seems pretty good to me.
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As a side note, I have read a quite a LOT of negative reviews concerning Behringer recording mixers. I own two of them, the 1204 I pointed to above, and their smaller 802 5-input mixer. I haven't had any problems with either mixer.
Also, as far as I can tell, most of the complaints aimed and Behringer mixers are by people who are comparing them with mixers that cost over $1000+. Well DUH? I most certainly hope that a $1000+ mixer performs better than a $100 or $160 mixer!
For the price I don't see how you can go wrong with a Behringer mixer. I haven't had any problems or complains with either of mine.
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By the way, if you are thinking that you might only need the 5-input mixer instead of the 12, let me point out that the 5-input mixer does not have a USB connection. So you need to buy the USB interface separate. By the time you've paid for both the 802 mixer and the additional USB adapter you may as well have just bought the 1204 and have more inputs available. ;}
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I hope you found this ramble at least interesting if not helpful.
Like I say, even if you don't consider the precise products that I've pointed to, you might still want to consider an alternative to relying solely on a computer's sound system.
You can either buy a really expensive computer, or you can buy a less expensive computer and a nice sound studio.
One way to think about it also, is that later down the road if you change computers, you'll still have the mixer and mics. That was my strategy and it paid off, because this is actually my SECOND computer. Well, that's because I originally started off with a quite old Dell Notebook. But when that Dell died, I was able to just plug this new Compaq right back into my mixer and off I go!
So that's my food for thought, for whatever it's worth. PC or Apple is meaningless to me. Just give me some good studio condenser mics and I'll be happy. ;}