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 Forum index » DIY Hardware and Software » Microcontrollers and Programmable Logic
DIY PC audio interface
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Oli



Joined: May 21, 2008
Posts: 246
Location: i think before i ambient
G2 patch files: 1

PostPosted: Tue May 05, 2009 2:06 am    Post subject: DIY PC audio interface
Subject description: How hard would it be?
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Hi,

I've been shopping around for a multi I/O audio interface for my PC, trying to get a decent but cheap home studio off the ground, and am a little surprised at the cost of interfaces such as M-Audio Lightbridge, or RME HDSPe RayDAT.

My focus in looking for an interface was to have multiple ADAT channels, which could then be expanded to break outs with something like ADA8000's.

I'm an electronic engineering grad, so had to wonder just how difficult it would be to make a basic digital backend interface like these? I had thought that without the analogue front end, then it would all be a fair bit cheaper.

I almost entirely use line level audio, and have no need for mic pre's included in an interface.

I've done some basic FPGA and microcontroller projects of course, but nothing much like these interfaces. I think there may be forum members with more experience of this kind of design; any suggestions as to the complexity involved?

I have some experience with analogue interfacing, and have studied digital systems, but have not dealt with streaming mutichannel digital signals.

The PC side of things is also a bit of a mystery to me, as I have never had to write drivers, and never done any audio software development at all. I had wondered if there may be reference drivers around for multichannel ADAT over Firewire, though I haven't found such. It seems that technology vendors are doing their own things with their software internals. I'm guessing there must at least be some standards for how drivers present their channels to DAWs.

I think the commercial interfaces also have varying degrees of DSP resources, and hardware (DSP?) mixing onboard, which I guess may be part of the cost factor, and perhaps much harder to match easily in a DIY project. Any thoughts on this? I have very little experience in modern studios, and DAW use, but I would imagine that hardware mixing/routing in an interface could be very important for managing latency where audio is routed through a few devices.

The ADAT (or other) analogue front end/breakout also doesn't seem terribly complicated. The better part of the ADA8000's appear to be firmly based on reference designs, though the analogue part looks as though it has been done on the cheap. Anyway, this aspect looks as though it could be manageable as a DIY module. Making it any cheaper than an ADA8000 is another matter, of course.

I imagine a system like this would have to manage issues such as clock synchronisation and jitter, memory bandwidth/throughput, and various other digital system issues which probably slip my mind at this time.

So, what I had wondered, is if it would be a reasonable, and worthwhile open source project to embark on? I think it is a system which could be quite nicely modularised for work on it's various components.

Personally, I am quite interested in developing my technical skills in this area. However, if there are others who have some experience with the design issues involved, and would be able to give some advice, then that would be really of great value. I wouldn't mind too much, investing in some development tools for this kind of work, as it would be in part benefical for my career (I hope). I don't always have the opportunities to do highly technical work in my job.

Any feedback would be much appreciated.

Cheers,

Oli

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dshay



Joined: May 04, 2009
Posts: 11
Location: Minnesota

PostPosted: Tue May 05, 2009 4:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Texas Instruments has a good sounding A/D chip, the 4222, they offer an evaluation board for sale, has SPDIF/AES outputs I believe.

That would get around writing drivers. My newest motherboard came with SPDIF built in.

When it comes to converters, Cirrus Logic, TI, Analog Devices and AKM are it. Don't look into anything else.

DIYing converters is insanity by the way. If you're smart enough to do it you should be working a job where you can afford Prism/Lavry/Cranesong type converters.

I suppose the economy is down though Sad

But the time it would take to DIY something like that you could afford an Apogee clock washing dishes.

But that's besides the point. The pride in DIY is a sickness. I made something DIY last year that I already have five of in commercial units. Just because I can.

I wish you the best.
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Oli



Joined: May 21, 2008
Posts: 246
Location: i think before i ambient
G2 patch files: 1

PostPosted: Tue May 05, 2009 11:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Dishay,

Thanks for your reply.

If I use a converter IC, I will most likely use an existing ADAT mutichannel device, similar to the ADA8000's. The other option is to build such a device from FPGA + peripherals. I think using SPDIF/AES doesn't really get around the need for a driver to handle mutichannel I/O. I've not used SPDIF/AES before, but isn't it only one stereo pair per electrical connection?

dshay wrote:
When it comes to converters, Cirrus Logic, TI, Analog Devices and AKM are it. Don't look into anything else.


Thanks for the tip. I was thinking of using Wavefront, for ADAT I/O. What do you think of these?

dshay wrote:
DIYing converters is insanity by the way. If you're smart enough to do it you should be working a job where you can afford Prism/Lavry/Cranesong type converters.


I've designed converters in uni, and it wasn't impossible. They were much higher speed than audio, but definitely not designed for sound quality. I was thinking to use IC's for that anyway, at least for starters. I wouldn't be trying to re-invent everything.

dshay wrote:
But the time it would take to DIY something like that you could afford an Apogee clock washing dishes.


Yeah, I am going to buy products to meet my needs. This would be more of a personal interest thing, and thought it might be a good project for the DIY/open source community. I'm still not certain how feasible it would be, as it is a bit beyond the range of my experience. I'm OK with taking on tasks beyond my experience though, as it is the only way to move forward, and I have pretty much always worked self directed.

Cheers,

Oli

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