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Old 28th September 2011, 03:27 AM   #1
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Default emulated crossover

I am considering building something like Linkwitz's "Pluto" system, but with a twist. The powered speakers would in this case have built-in USB DACs and wireless usb hubs. These would end up plugged into a computer, which would "see" two stereo devices, each one per speaker.

This seems easy enough. Now I get to the crossover part. I would like to emulate the active crossover by using the computer to split the audio, apply filters, and redirect the audio to the separate USB devices.

Now, the only software I have been able to find that MAY do this is LSPCAD Pro, which is $1100 and has WAY more functionality than is needed.

The other way I could think of is some kind of solution using linux, pulseaudio, and multiple instances of a graphical EQ.

But I'm a novice when it comes to these gritty aspects of digital audio. Does anyone have any suggestions on how to implement a "computer" crossover? For less than the price tag of lspcad?
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Old 28th September 2011, 03:30 AM   #2
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I think this would be better in PC Based. Moving there.
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Old 28th September 2011, 03:56 AM   #3
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How will you deal with the skew? USB is serial and one speaker will get it's samples before the other. The timing details are determined by the USB host and you have no control.
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Old 28th September 2011, 04:14 AM   #4
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It strikes me this is one case where you definitely do not want asynchronous USB. The skews for adaptive ('old technology') USB will just translate into relatively minor time delays (different buffer lengths perhaps) but with asynch USB you'd have two totally asynchronous clocks in the two USB DACs so there's in theory no bound to the skew.
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Old 28th September 2011, 06:49 AM   #5
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Async mode would require async reclocking in SW (libsamplerate) but that would wipe out the actual advantage of async USB.

I do not have any windows experience, but it is feasible to make it in linux, using brutefir. You can do the channel routing directly in alsa, no need to complicate it with pulseaudio. But be prepared to overcome a number of issues which would arise along the way, definitely not a project for an evening.

BTW, the new USB drivers in linux alsa commited to GIT last month are capable of reporting the samples being currently transferred to the USB sound card down to 1ms precision.

Last edited by phofman; 28th September 2011 at 06:51 AM.
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Old 28th September 2011, 11:00 PM   #6
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Well, skew is not something I had thought about. The more I read up on what you guys have said, the more I am thinking that my idea, though neat, is beyond my skill level.

I still would like to build a Pluto-style system, though I may consider a non-diy alternative to the crossover (Behringer makes a digital xo I am thinking about).

Not sure how else I would wirelessly transmit audio at 24/96. I may just have to build something more conventional.

Thanks for the responses! Diyaudio rocks.
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Old 3rd October 2011, 03:26 AM   #7
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couldnt you use a syncronous master clock? whats your budget? because you can use allocator a specific program for digital XO combined with a multichannel usb-i2s convertor like the exadevices unit
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