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Old 16th April 2007, 09:19 PM   #1
thadman is offline thadman  United States
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Default PC crossover with IIR filters, affordable?

Im wondering how much a dedicated PC would cost that incorporated all the digital filters and the whatnot that was detailed in shinobiwans thread.

The thread is nearly 2 years old now and is composed of 756+ posts (I dont have the time to read that entire thread). Keeping that in mind and coupled with the fact that technology progresses at an amazing rate, im not sure what an affordable setup would be today and how it would compare to a DCX2496 + DEQ2496 setup.

I have the technical prowess to build a computer, and have built several in the last few years. I'd love to keep the project down in cost and with the extremely competitive prices (Intels QX6800 is supposedly dropping in price to $241 soon to combat publicity from AMDs barcelona) it seems like a perfect time.

What soundcard(s) would you recommend?

Is the software memory intensive and if so how much is recommended?

Where can I purchase the software? Is it available on torrents (project is out of question if software is unavailable online or costs $$$$$)
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Old 16th April 2007, 09:48 PM   #2
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http://www.thuneau.com/allocator.htm + MAudio Firewire 410.

Perfection isn't free.
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Old 17th April 2007, 12:17 AM   #3
thadman is offline thadman  United States
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How many channels does the M Audio soundcard support? Does it offer Internal routing of digital signals? Multiclient drivers that support simultaneous use of ASIO, DX and MME clients?

Will this software coupled with that soundcard provide DRC? It seems as if its limited to 42dB slopes? Am I wrong?

Will it do everything and be as powerful as the setup Shinobiwan describes?

I'd like something *somewhat* affordable (those prices for the software are perfectly reasonable), but it has to vastly outperform a DCX2496 + DEQ2496 or be comparable to a DEQ, otherwise its hard to justify given the already high investment. I dont want to settle for 42dB slopes.

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Old 17th April 2007, 11:17 AM   #4
thadman is offline thadman  United States
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Old 18th April 2007, 12:28 AM   #5
thadman is offline thadman  United States
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up, nobody? cmon I know some of you are running these setups.
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Old 18th April 2007, 03:42 AM   #6
Daveis is offline Daveis  United States
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I'm using Allocator Lite from this place http://www.thuneau.com/allocator.htm

I'm using an Intel Core Duo which is overkill.

Also using an RME HDSP9652 card which has ADAT outputs. RME has a newer card with AES/EBU outputs that might be better.

It works in two ways...

a) cdplayer or cdjukebox into sound card and right back out the same sound card
b) windows media player, DVD soft-player, or Winamp ASIO looped back through extra physical cable all within the same sound card.

DRC would require a convolver along with the IIR style filters that Thunea provides. If you want to play DRC you may want to use a purely FIR based convolver.

Some examples of that are
a) Brutefir on Linux
b) sourceforge convolver
c) Voxengo Pristine space and other commercials ones

Want more than 42db slopes? I would use the lowest order slope you can get away with if you are using IIR filters. In the end I always came back to 24db slopes as a good compromise.

I switched from DCX2496 and wouldn't think of going back to DCX.
My DCX2496 never got modded other than a remote volume control.

My main reason for the PC over DCX2496 is
a) Didn't have the skill or interest in modding the DCX2496 and it was trivial to hookup a good external DAC to a sound card.
b) DCX2496 doesnt make playing with DRC easy
c) Limited to 3-way speakers and I needed 4-way
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Old 18th April 2007, 11:56 PM   #7
thadman is offline thadman  United States
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Why would you recommend using the lowest slopes? Whats the benefit? IIR filters shouldnt screw with phase or group delay, so why not go as high as possible (until you meet diminishing returns and its a BRICK wall)?

Whats RMEs newest card called? How many outputs does it have?

What exactly is an FIR filter?
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Old 19th April 2007, 01:58 AM   #8
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Quote:
Originally posted by thadman
What exactly is an FIR filter?
http://www.dspguru.com/info/faqs/firfaq.htm
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Old 19th April 2007, 03:14 AM   #9
Daveis is offline Daveis  United States
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Quote:
Originally posted by thadman
Why would you recommend using the lowest slopes? Whats the benefit? IIR filters shouldnt screw with phase or group delay, so why not go as high as possible (until you meet diminishing returns and its a BRICK wall)?

Whats RMEs newest card called? How many outputs does it have?
Sure one purpose of the crossover is to separate the duties of your drivers. But it's also to "blend" the difference in sound of different drivers so it appears seamless. In listening tests, I prefer 18db or 24db crossovers with most music. I might occasionally find one song that sounds better with a higher order crossover.

If I remember only the 6db IIR filter maintains phase if that's important to you. I believe I remember B&W claiming they used simple 6db crossovers in their speakers. How they get away with this I don't know. My only other commercial 6db crossover speaker was a Thiel CS1.2 two-way. It crossed over at around 2500hz.

IIR filters(2nd order and above) and their analog equivalents do alter phase. It's FIR filters that can be linear phase.

IIR's main benefits are that
a) they emulate the sound of passive crossovers they replace.
b) low latency. An IIR filter can have a latency of 6 milliseconds. The practical importance of this is that you can filter live television or DVD's with no audio-video synch problems.
c) The low latency doesn't come at the cost of high CPU usage. My dual core Intel processor can do a 4-way crossover with 4% load.

FIR filters are widely used in signal processing. But for audio, I think FIR filters get interesting when you do start using them to alter phase as in DRC. I have no practical experience with this other than to say that the non-DRC FIR filters I tried sounded "clean" but somehow sterile.

RME cards are good but expensive ($600). Rather than getting the HDSP9652 I wish I would have gotten one of these HDSPAEA32 cards. But all these cards have 24 or 32 outputs at 44.1khz. You can S/MUX multiple outputs to get 24/96 sound but you will have half the channels.

http://www.rme-audio.com/english/premline/hdspaes32.htm

But these assume you are using external DAC's since they are either ADAT or AES/EBU output. I am sure there are good 8-channel (or more) sound cards with decent analog outputs for much less money.

Ok, and after all that. Do I think digital crossovers are better sounding than a good analog crossover? I'm not so sure after playing with it for 2 years.
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Old 19th April 2007, 11:06 AM   #10
thadman is offline thadman  United States
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Would Digital Room Correction (implemented correctly) yield the same benefits of a dipole setup (ie lack of bloated, boomy bass and no medley of room nodes?)
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