USB Sound Card Design questions

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Hi there,

My plans final aim is to have a 8 to 10 input sound card which will enable me to record the tracks seperately in Windows.

My thoughts so far are to have the 10 xlr/jack inputs going through an ADC and then to somehow pass this down either USB or SPDIF to the PC. What I dont understand about SPDIF is can you then seperate out the different channels like you can with the inputs on my current 2in2out usb soundcard?

Any ideas are welcome, thanks!
 
Hi will,
If you want to DIY a 8 to 10 input USB sound card, you need a LOT of experience with USB and digital technology in general. Or you need to find a very self-contained chip that matches you requirements closely, which I suspect you won't find. The closest you can get are probably the TI USB Streaming controllers, which are still quite a challenge to say the least.

Concerning the SPDI/F solution, you would still need another sound card in your PC to receive the SPDI/F lines. Oh, and if you didn't know already SPDI/F is only lossless for Stereo, not for multichannel so if you want to record I wouldn't recommend to do it via multichannel SPDI/F.

This is all under the suspicion that you are not that proficient with USB or digital sound or digital. I'm not a pro either, so that's just another amateurs view. But I was trying to do something quite similar to what you are planning some time ago and I decided to delay that project until I'm a pro. :p
 
I'm another who's considdered such a project, and decided it would be quite a challenge.
My plan was to get as much of the engineering ready-made (as high-speed digital circuitry is a science in itself) by basing the interface on an FPGA board with a PCI interface. This would give an "internal" interface, rather than an external one connected by USB etc, but it does put you in charge of the entire design.
Taking this aproach, you should basically just need to connect all the pins of your ADCs to the FPGA, and the rest of the design can be done in "software". You might need a bit of logic for distributing clocks etc, but the amount of electronic construction on the digital side should be quite small. If I remember rightly, Analogue Devices to a stereo ADC which can be cascaded in a chain of up to four - giving 8 individual inputs.
The catch with this plan is that these FPGA boards are very expensive, and from what I understand the learning curve is pretty steep.
 
Unless you have already worked with FPGA, I'd rather recommend using one of the USB 2.0 audio chips that are available than beginning FPGA with such a complicated task. There are ICs available from VIA and CMEDIA, which feature several inputs and a USB 2.0 interface, but as you probably already suspected those are hardly available to DIY persons. Especially the one from VIA.
VIA Vinyl EnvyUSB 2.0 Audio Controller - VIA Technologies, Inc.
C-Media Electronics, Inc.
 
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