exaU2I - Multi-Channel Asynchronous USB to I2S Interface

[rsdio]

In terms of a DIY solution that can work with standard USB Audio Class compliant drivers, the key is selecting a USB chip which is programmable. The popular DIY chips are from FTDI Chips, and they are (nearly?) all not programmable, thus USB Audio is out of reach.

Any standard processor chip with USB Device capabilities would be a good choice. Off the top of my head, there is Microchip PIC and Cypress EZ-USB FX2. If you actually want to perform DSP on the hardware instead of in the computer, then a good choice would be the Texas Instruments TMS320 family. I am currently working on a design using the TMS320VC5506, which is a massively powerful DSP with onboard USB. It's technically a 16-bit processor, but it can access 32-bit samples in memory and has 40-bit registers - all fixed point. A better choice might be one of the 32-bit members of the family, and the floating point models might be much easier to program.

In any case, having a processor instead of a drop-in part like the FTDI Chip allows full control over USB, such that USB Audio 2.0 could be implemented. The problem here is that USB Audio firmware development costs something like $50,000 - or at least that's the quotes I've seen. I do know that the USB product development I have done is similarly expensive due to the time it takes to create firmware that works flawlessly on custom hardware.

Perhaps some day the DIY community will have an open source USB Audio firmware, but that could be difficult considering that many parts of the firmware are in assembly language, which is obviously not as portable as Standard C. Another problem is that each processor has its own USB library, and they are not compatible, making it that much more difficult to have one open source USB Audio solution that works everywhere.

[exa065]

Originally Posted by Russ White

None yet...

The reason is I want a solution that conforms to the USB audio class 2 spec. I don't want custom drivers if I can avoid it.

In the case of windows one has little choice. But in the professional audio (recording and mastering) arena where I get most of my music from - that fact matters little as almost all the studios use Macs anyway.

That is what I hope to achieve. A standard based approach to USB audio.

But honestly, in this context, who cares about my solution, or any off the shelf solution (like yours)? I was looking at a way for people to possibly come up with their own. That what the DIY section of the forum is all about. If you have some commercial interest that is fine. Just call it what it is.

Cheers!
Russ

Well, I have as much commercial interest as you.

I am very interested to share my passion for realistic music reproduction, but unfortunately original research and development costs money. Let's face it - there is more in-house developed know-how in the exaU2I then in the Buffalo III DAC. That's why competition to exaU2I is slow to appear.

My way of shearing is to make this research available to the DIY community for fraction of the cost of comparable devices on the CASH list at Computer Audiophile | High-End Audiophile Music Servers.

Regarding USB audio class 2 spec - inside there is everything AUDIO that one can think of. It is designed to serve wide spectrum of consumer applications. It is hard to achieve audiophile-grade sound with such a multifunction tool. I prefer the specialized approach. I need better than standard approach.

Finally on the Mac-Windows argument - with a true asynchronous driver / interface implementation, it doesn't matter what is the computer platform of choice. Does it matter if you use Mac or Windows to stream out audio to something like Squeezebox?

Since you don't recommend any existing USB to I2S interface on Earth, let me rephrase my question:

Is it better to use SPDIF with Buffalo DACs instead of proprietary exaU2I?

On one side you have a jittery, legacy, limited-bandwidth interface.
On the other side - the risk to use something proprietary, but innovative and delivering results now.

Regards,

exa065

[rsdio]

Originally Posted by exa065

Regarding USB audio class 2 spec - inside there is everything AUDIO that one can think of. It is designed to serve wide spectrum of consumer applications. It is hard to achieve audiophile-grade sound with such a multifunction tool. I prefer the specialized approach. I need better than standard approach.

The way you've worded this, it seems to imply that USB Audio 2.0 Class specifications would somehow compromise the design of the exaU2I. But when I read carefully, I see nothing specific. Maybe I'm must misinterpreting due to context.

Would you care to qualify your statements? Apart from the FT2232H, is there any reason why a future revision of the exaU2I hardware could not be USB Audio 2.0 Class compliant without sacrificing any of the existing audiophile-grade sound?

In my experience, the Bulk Transfer mode of the exaU2I puts it at risk of losing samples. Granted, such an occurrence would be incredibly rare, but the fact is that the USB Host (your computer) will not guarantee bandwidth for Bulk Transfer. It's designed for disk drives and other non-real-time devices. One significant change if the exaU2I were to become USB Audio Class compliant is that it would then be using Isochronous Transfer mode, which is absolutely guaranteed bandwidth. Audio and other guaranteed bandwidth, real-time data is exactly what ISO is designed for. In other words, the audiophile-grade quality of the exaU2I would only be improved by switching to USB Audio, although it would require a hardware change.

I will admit that some of the other USB Class specifications are crap, e.g. the USB-MIDI spec is so bad that it compromises the timing of the MIDI events - needlessly, too, I would add. Conversely, USB Audio seems fully capable, and I am aware of no shortcomings. If you are aware of shortcomings in the USB Audio specification which would sacrifice audiophile-grade quality, then I would be very interested in discussing them.

To clarify: I am not making any claim that the exaU2I does not offer the best audiophile-grade sound. I'm sure it does. That is a function of the hardware, and Bulk data dropouts are probably unlikely. However, USB Audio Class compliance would make this accessible to more people with less effort and 100% reliability, so I'd like to see a way to combine the high-grade hardware with the convenient, driverless link.

[exa065]

Originally Posted by rsdio

The way you've worded this, it seems to imply that USB Audio 2.0 Class specifications would somehow compromise the design of the exaU2I. But when I read carefully, I see nothing specific. Maybe I'm must misinterpreting due to context.

Would you care to qualify your statements?

I just said that It is hard to achieve audiophile-grade sound with such a multifunction tool. Sure there are fine USB Audio 2.0 implementations out there. I am disappointing by the complexity required to achieve something straight-forward and simple. Your previous post illustrates my point.

Who knows what is the best technology of the future to stream out sound from a computer? I will pick the easy one for the next exa.

[Russ White]

Originally Posted by exa065

Well, I have as much commercial interest as you.

exa065

Oh you do? That's great to have out in the open. So why not behave like a vendor?

You are the only person who brought up my work. I had no intention of doing so. I also had no intention of mentioning your work in any unflattering way. Yet you seem to have some axe to grind. Your wild and inaccurate assertions don't make you look any better either.

Remember I am only part of this conversation because you wanted me to be. I would not have posted anything further if not for your invitation to do so.

I am genuinely interested in spawning a new conversation in a new thread about a similar topic only because I think its fun to design things from the ground up. I bet many people would get a lot more out of learning how it works, then simply buying something. I understand there are people for whom just buying something is the best option. That's quite fine, but then there are people like me for which that is simply not enough fun.

My post was simply a pursuit of my hobby. You must realize that your response seems a defensive reaction to alternative views. That kind of reaction seems very out of spirit on this forum. I understand you must have a lot at stake, but this is not the place to make that stand.

I wish you well, but remember this is the DIY forum. It is OK to post things that are on topic and encourage DIY pursuits. If you think it should be all about your product, then this thread does not belong on this forum.

Cheers!
Russ

[Coris]

Originally Posted by Russ White

If you think it should be all about your product, then this thread does not belong on this forum.

Cheers!
Russ[/QUOTE]


You do in fact think that the thread "Buffalo III - flexibility without compromise." is all about your product... You can actually not tolerate something else than exclusively about Buffalo on that thread. You do so! You also rejected many times ExaU2I from your own thread, because was about "miss leading"... It does your thread belong to this forum?

Not a good point to be so ironical against somebody`s else work, or minimise it to get the focus on yours... A little bit more modesty from your part is also strongly recommended... You have the moderation rights on your thread, but not the "teaching everybody everywhere" right yet (on this forum)...

I can suggest you to pay a little bit more as Vendor and maybe you will get the moderation rights over the entire DIY forum, so you could easily delete everything which is not belonging to this forum (in your conception...) And be then the DIY world Boss.

Cheers!


Sorry Exa for this out of topic post, but I had to pointed accordingly the intervention above...

[exa065]

There is a new OS X driver beta uploaded on the exaDevices download page.

One of ou users have identified an issue when the driver is used on OS X Snow Leopard. The Audio Midi application stopped working. Please don't use the previous version and download the new one dated 2010-10-17. Contact us from the support page on exaDevices.com if you need any assistance.

With this issue uncovered unfortunately we will not make any further attempts to support OS X Leopard.

Thank you again to all users that provided feedback.

Best regards,

exa065

[exa065]

Originally Posted by Russ White

Oh you do? That's great to have out in the open. So why not behave like a vendor?

Cheers!
Russ

Russ,
The readers will decide for themselves who behaves like an honest vendor. If you are interested to have a factual discussion, I am prepared to address any of my statements that you find wiled or inaccurate.

You didn't reply to the questions that matter to the DIY users regarding achieving the best sound with a Buffalo DAC. Many of them consider various I2S devices. It appears that you are looking for end to end TPA solution and nothing else works for you.

I am disappointed to see this useless fight on my thread. Long ago on the about page of the TPA website there was a BS meter. I don't know why it was removed. I really liked it. Anyway it was showing around -20dB. On this thread we are aiming for -120dB.

[exa065]

Hello everybody,
Thank you for the quiet support. I understand that it is hard for you to speak out because you need good relations with all parties involved in this discussion. The last 24 hours were the all-times best for exaDevices. We've never received so many orders within 24 hours.
exa065

[Russ White]

Exa ...

Why do you surmise I care what products people use with our DACs. I don't in the least. Sure I am developing something I think will be awesome, and I hope people choose to use it. But I have never had a problem with your work. What I did not want was our vendor thread to become a place where others tried to advertise for free. Nothing more than that.

I don't feel the need to respond to a completely subjective question. People can decide for themselves what they like.

I have no urge to fight, I really don't even feel engaged in one. It is disappointing to see you are feeling that way.

Where do you feel I have attacked you in any way?

My only goal in posting on this thread was not to lose track of some interesting information someone had posted and to encourage people who might want to try it to start a thread. How does that offend you? It in no way benefits me. It only benefits hard core DIY folks.

Best of luck to you.

Cheers!
Russ