Digital active XO+eq using a PC+soundcards+BruteFIR? - diyAudio
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Old 15th September 2003, 03:26 AM   #1
tcpip is offline tcpip  India
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Default Digital active XO+eq using a PC+soundcards+BruteFIR?

Hi all,

This is actually a follow-up from an earlier thread I had started in this forum, about active XO designs. That discussion went into using digital active XO+eq like the Behringer or the Driverack, and taught me a lot. Can't thank all of you guys enough. (I guess you are getting tired of receiving all this adulation... )

While absorbing and digesting all that, I strayed into other forums, and chanced upon discussions elsewhere where people were trying to build high-end CD players using $20 computer CD-ROM drives. Thorsten's evil twin was posting there, and many other very experienced people. The thread at some point fragmented into two, pursuing two different approaches to the same goal. Most interesting, both the threads. But that's where I learned about BruteFIR. And this brought me right back to active XO for speaker building.

BruteFIR allows me to use an ordinary Intel computer to do real-time digital filtering on digital audio data. This means that I should be able to take digital or analog inputs into my PC, use BruteFIR to create the equivalent of Driverack or Behringer units, and then pump the sound out through a decent multi-channel sound card (many pro audio cards have six to eight analog output channels).

Will this be a good idea? This sounds like a great way to do active filter prototyping, and then when the design is frozen for a particular box, you can build a hard-wired analog active XO+eq for the box using (low-tech, I know) NE5532 and passives, at very low cost. And then move ahead with your PC to the next speaker design project. To my newbie brain, this sounds like the ideal DIY speaker building tool, at low cost, with high flexibility, allowing oodles of tweaking, and building a sub-community of BruteFIR users exchanging tweaks in terms of config files.

Will this work? It's possible to build a PC with no fans for cooling... that's a known problem with known solutions. So adding the PC to the chain will not add ambient noise. And it's possible to eliminate drives from a PC, thus removing still more noise. You can build a PC which boots from a CD-ROM and works entirely out of ramdisk. Such a PC probably can be powered by a conventional transformer+bridge+filter caps combo instead of the noisy fan-cooled SMPS. (Just Google for "low noise PC" and "silent PC" for lots of links.) Also, the RFI in the PC should not affect the sound too much if you use good sound cards... most pro audio workstations are built around them nowadays, I'm told, even in recording studios. And the threads I mentioned earlier (CD-players using CD-ROM drives) are discussing such hardware already.

(All my software-related comments are related to Linux. I'm somewhat computer-challenged; I can't seem to get anything done easily with Microsoft operating systems, other than MS-DOS. My laptop runs Linux.)

Please, what do you guys think? My goal is to get active-XO speakers designed and built quickly without having to invest in a Behringer. Steve and others have already said in my earlier thread that it's quite easy to translate the settings of a Behringer/Driverack into an equivalent hard-wired analog circuit design. Such a circuit will be as complex as SL's eq circuit for his Phoenix or Orion, I guess.

Tarun
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Old 15th September 2003, 03:33 AM   #2
agent.5 is offline agent.5  United States
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The answer is yes. I think more than one person here is working on similar project. I am using a strip down Window 98SE booted from a compact flash disk. I am still debating on the software. Most likely, WaveWarp from

http://www.soundslogical.com/
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Old 15th September 2003, 03:48 AM   #3
tcpip is offline tcpip  India
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Default Another thread, another approach

I've checked an earlier thread started by NappyLady, about using Creative Soundblaster Live with special device drivers for something like this. My asking this in a separate thread was with the hope that we could look at a solution which was independent of a particular sound card. That Soundblaster solution was tied to the device drivers of that card's DSP chip. I thought I'd just explain...

And if we can go open source with the software, and make it totally sound-card independent, then different members can actually try various different sound cards without affecting the (complex) software at all, and get solutions at different price points. Some of you can also make products out of such work and offer them for sale without software licence fees.

And Agent.5, thanks for the pointer. Will take a look at the software you've mentioned. How small is the practical lower limit of your flash RAM with your approach?

Tarun
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Old 15th September 2003, 03:51 AM   #4
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You may find this site interesting:



http://home.pacbell.net/donwm/


The only issue that might rear its head is if you incorporate room EQ into your analog units, then move the speakers or the lsitening position significantly. This will stuff up the EQ.

Cheers

Steve
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Old 15th September 2003, 03:54 AM   #5
r0cket- is offline r0cket-  United States
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It's probably workable, but I think it would cost quite a bit more than a decent Behringer X/O anyway, so I'm not sure what the point is. I mean, a suitable sound card alone will probably run upwards of $150. And that's not even taking into account the cost of the PC (which will be pretty hefty if you want it to be silent, use a linear power supply, and be completely RFI-shielded) or the time involved in building a boot image for it.

Additionally, correct me if I'm wrong, but aren't crossover points properly determined mathematically anyway?

It's not a bad idea, but I don't think as a stand-alone device the price/performance ratio doesn't even come close to beating that of a traditional commercial or DIY X/O. Of course, as an addition to a home theater PC, I think it would certainly have some use.
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Old 15th September 2003, 03:56 AM   #6
agent.5 is offline agent.5  United States
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The OS will comes in less than 60M and CF can go as high as 2G. You can store the OS and related software on a 128M CF (cost is reasonable and no hard drive required)
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Old 15th September 2003, 04:13 AM   #7
tcpip is offline tcpip  India
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Quote:
Originally posted by sfdoddsy
You may find this site interesting:

http://home.pacbell.net/donwm/

The only issue that might rear its head is if you incorporate room EQ into your analog units, then move the speakers or the lsitening position significantly. This will stuff up the EQ.
Thanks, Steve. I checked that site quickly; it's very interesting. Have bookmarked it. And you're right about that room eq bit. Don't know how to get over it, unless I leave that PC+BruteFIR in circuit permanently.

One other problem that's coming up with my own idea as I write, is that I probably cannot get decent sound quality using separate inexpensive two-channel sound cards... I'll need one card to output at least six analog outputs. This is because I'll need all outputs to be clock-sync'd. If I want to do external clock-sync, then the sound cards will probably become more expensive than the Behringer. And multi-channel cards cost a fair packet... the Delta 1010 (the one in the site you referred me to) lists at $799, and will probably sell for $400-500. Once again, the Behringer is cheaper.

Quote:
Originally posted by r0cket-
It's probably workable, but I think it would cost quite a bit more than a decent Behringer X/O anyway, so I'm not sure what the point is. I mean, a suitable sound card alone will probably run upwards of $150. And that's not even taking into account the cost of the PC (which will be pretty hefty if you want it to be silent, use a linear power supply, and be completely RFI-shielded) or the time involved in building a boot image for it.
You're right about the sound cards, so I'm having doubts myself. But a PC can be quite inexpensive, specially if you take a PC motherboard which is a couple of years old. The other tweaks to make it quiet don't cost much money.

Quote:
Additionally, correct me if I'm wrong, but aren't crossover points properly determined mathematically anyway?
I didn't understand this point. Can you explain?

Quote:
It's not a bad idea, but I don't think as a stand-alone device the price/performance ratio doesn't even come close to beating that of a traditional commercial or DIY X/O.
I'm having doubts too... the sound card cost will be the determining factor, no doubt. I had been dreaming of using a set of three inexpensive stereo cards, but NappyLady's thread already talks of clock drift problems... Sigh.

Tarun
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Old 15th September 2003, 04:15 AM   #8
tcpip is offline tcpip  India
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Default Size of solid-state bootable disk

Quote:
Originally posted by agent.5
The OS will comes in less than 60M and CF can go as high as 2G. You can store the OS and related software on a 128M CF (cost is reasonable and no hard drive required)
Thanks. I think the figures for Linux will be similar. People routinely do minimal Linux bootables for 40M. I didn't know how small Win98 could go to.

Tarun
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Old 15th September 2003, 04:59 AM   #9
r0cket- is offline r0cket-  United States
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Well, my understanding of crossovers of any sort is that you determine the crossover points and slope and whatnot mathematically via the TS parameters of the drivers involved and the cabinet dimensions, etc. So I guess I just don't really understand why you would necessarily want an active X/O that allows you to "experiment," as you say, when the optimal values are easily determined on paper or via software simulation. An EQ, sure, but not an X/O.

The thing with the sound cards is that in order for any of it to be effective, you need something with 4 or 6 analog channels that each have perfectly flat frequency response from like 10Hz-40KHz. That's going to be very expensive.
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Old 15th September 2003, 06:27 AM   #10
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Ideally you would have your crossover model, and then measure the drivers in the baffle to make sure everything is perfect, and adjust or tweak from there.

Cheers

Steve
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