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Single PC solution - Use of 2 USB sound cards as crossovers using PAX Rack
Single PC solution - Use of 2 USB sound cards as crossovers using PAX Rack
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Old 17th April 2019, 11:43 PM   #1
Tromperie is offline Tromperie  Australia
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Default Single PC solution - Use of 2 USB sound cards as crossovers using PAX Rack

In this thread Pulseaudio Crossover Rack - multi-way crossover design & implementation with linux, I asked whether it is possible to use two separate USB sound cards, each placed in separate speaker boxes, as crossovers controlled by PAX rack. It is my hope to get rid of all electronics between one PC and the active speakers a one box solution.

phofman answered with this;
Quote:
I do not think there is any conflict. What the current version supports out of the box:

1 soundcard = both left/right channels of one branch (bass, mid, high, whatever). The branch is always stereo.

But what you want is:

1 soundcard = left channel of bass branch + left channel of mid branch + left channel of high branch

To solve, just create one "virtual" multichannel soundcard and route branches to respective channels as needed. Alsa-lib below pulseaudio will split the channels to corresponding physical cards, according to the multi config in .asoundrc.

The only issue is configuring stable sound card IDs since identical USB sound cards have identical names. This has been a common requirement too, solved by adding udev rules. A very nice tutorial is Persistent USB Mapping of Audio devices (Linux) * dh1tw/remoteAudio Wiki * GitHub - the card text ID (e.g. SPEAKER or HEADSET in that tutorial) will be tied to the fixed usb port. That text ID will then be used instead of the card numeric ID in the .asoundrc multi configuration (hw:NAME instead of e.g. hw:0).
Persistent USB Mapping of Audio devices (Linux) * dh1tw/remoteAudio Wiki * GitHub

Having also offered his assistance, for which I am grateful, I will now chronicle my (mis)adventures for others (foolish enough) to follow this path.

I plan to test with two cheapy USB sound cards, using RJ45 to USB extension adaptors and Cat5 cable. If successful, I plan to then route the cable through the walls, as is the current balanced cable.

More details to follow.
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Source: LMS 7.9.2 on FreeNAS, PiCorePlayer * Storage: FreeNAS 11 * DIY PGA2310 * Amps: 8 x LM3886TF
Xover: 24dB @ 300 and 3kHz * Speakers: CNC cut 54 laminations * SB 10", SB 5", VIFA 1" * Remote: Squeeze Control

Last edited by Tromperie; 17th April 2019 at 11:45 PM.
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Old 19th April 2019, 01:33 AM   #2
iperv is offline iperv  Italy
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Very interesting.
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Old 19th April 2019, 04:54 AM   #3
phofman is offline phofman  Czech Republic
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USB has some length limits, make sure to check if your final soundcards work OK with the extension adapters of choice. If a USB storage or HID device drops a packet, no problem, the data is resent or ignored, but in this case every data drop will result in an audible click.

Also some RF45 adapters work only with USB1.1 (12MHz). Check if it is compatible with your soundcards.
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Old 21st April 2019, 02:38 PM   #4
arcgotic is offline arcgotic  Romania
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Do you know, in Windows is possible this? Using multiple USB soundcards?
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Old 22nd April 2019, 04:34 AM   #5
Tromperie is offline Tromperie  Australia
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Quote:
Do you know, in Windows is possible this? Using multiple USB soundcards?
This isn't about Windows, so you are way OT.
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Source: LMS 7.9.2 on FreeNAS, PiCorePlayer * Storage: FreeNAS 11 * DIY PGA2310 * Amps: 8 x LM3886TF
Xover: 24dB @ 300 and 3kHz * Speakers: CNC cut 54 laminations * SB 10", SB 5", VIFA 1" * Remote: Squeeze Control
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Old 7th May 2019, 04:01 PM   #6
arcgotic is offline arcgotic  Romania
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I know I was OT, was just interested if you tried this also in Windows and what you succeeded.
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Old 7th May 2019, 07:11 PM   #7
phofman is offline phofman  Czech Republic
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Quote:
Originally Posted by arcgotic View Post
I know I was OT, was just interested if you tried this also in Windows and what you succeeded.
Configuring device merge in windows? I have never heard of that. Like many other things in audio setup.
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Old 8th May 2019, 04:00 AM   #8
Tromperie is offline Tromperie  Australia
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Quote:
I know I was OT, was just interested if you tried this also in Windows and what you succeeded.
I thought this might be obvious from my signature.
__________________
Source: LMS 7.9.2 on FreeNAS, PiCorePlayer * Storage: FreeNAS 11 * DIY PGA2310 * Amps: 8 x LM3886TF
Xover: 24dB @ 300 and 3kHz * Speakers: CNC cut 54 laminations * SB 10", SB 5", VIFA 1" * Remote: Squeeze Control
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Old 8th May 2019, 04:13 AM   #9
picowallspeaker is offline picowallspeaker  Italy
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Putting the electronics inside a speaker box is the worst scenario.
You would say: but the Pros are doing it!
For me it's very bad to put the passive crossover in that environment.
Not to mention the cables passing in the wall ( oh, but they carry digital; but I see someone complaining about the length ... )
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Old 8th May 2019, 05:08 AM   #10
Tromperie is offline Tromperie  Australia
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pico,
Your opinion is just that. I already run balanced feeds through the wall to my active speakers. Noisy? NO. Thanks but no thanks.
__________________
Source: LMS 7.9.2 on FreeNAS, PiCorePlayer * Storage: FreeNAS 11 * DIY PGA2310 * Amps: 8 x LM3886TF
Xover: 24dB @ 300 and 3kHz * Speakers: CNC cut 54 laminations * SB 10", SB 5", VIFA 1" * Remote: Squeeze Control
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