Prototype For Sale

I'm no longer in need of my original prototype, so I'm going to sell it as-is or part out the individual components. I plan to post the sale on eBay, Craigslist and some Facebook groups dedicated to audio. When I get a chance to take some photos, I might update this post. If you are interested, feel free to contact me at gregg dot plummer at gmail dot com.

This first prototype consists of a combination of amp modules and a FireWire audio interface in a utilitarian aluminum chassis. I was pretty concerned with overheating because of the 5 high powered amps so I used a fairly thick aluminum to help dissipate any heat. It's also vented at the top, just above the amps and there's a very quiet 120mm fan to blow air out the back. BTW, I worked with a mechanical engineer who did some thermal analysis on the prototype to make sure we dissipated the heat. It was probably a little overkill. My price for the prototype is $825. My cost, not including the considerable amount of time designing, building and testing were about $2,500.

The components included are:

Aluminum Chassis - this includes the 120mm fan, special mounting plates for the power supplies and mounting brackets for the audio interface. On the back is the A/C receptacle with a switch (A/C line cord included) and a 10A Bussman time delay fuse socket. On the front, there's a momentary pushbutton switch that has 2 operation modes. In one mode, the audio interface is powered on while the amps remain off. The other mode switches on the audio interface and all the amps. Not sure if anyone would be interested in this because the layout is designed specifically for the rest of the components. The price for the chassis is $295 $100.

Power supplies - At the time of this design, the only practical choice for the system were linear power supplies. I really wanted to incorporate SMPS (switch mode power supplies), but ones with the characteristics I wanted for this high-quality audio application were not available. I used different amps for the front and rear channels, so the system utilizes 2 different power supplies.

• The power supply for the rear channels includes a 400 VA (115/33 Vx2) toroidal transformer and a Hypex HG power supply. My prices are $65 for the 400VA toroid and $100 for the Hypex HG PS.
• The power supply for the front channels includes a 1000 VA (115/45 Vx2) toroidal transformer and a Hypex HG power supply. These are $100 for 1000VA toroid and $100 for the Hypex HG PS.

Amplifier modules - I used the highest quality Hypex UcD amp modules that were available at that time. This prototype only needed to provide power to 5 channels because, in a typical 5.1 home theater system, the subwoofer is self-powered (channel .1). To each amp module, I attached an aluminum plate heat sink with fancy Neutrik speaker binding posts.

• The 3 front channels - right, center, left use Hypex UcD400AD amp modules. These are each rated at 400W RMS into 4 ohms. Unfortunately, only 2 of the 3 are currently working. The one I was using for the center channel has a faulty component that causes the amp to output a terrible thumping sound. So, I'm including it for free with either of the other working modules. I think it just might need a new cap but I'm not sure and Hypex no longer services this amp. The price for the working UcD400AD modules is $85 each or $165 for the pair. 
• The 2 rear surround channels use Hypex UcD180AD amp modules. They are rated at 180W RMS into 4 ohms. My price for a UcD180AD module is $65 or $125 for the pair.

Audio interface - this is the device that your PC will use as the audio device or soundcard in your HTPC. It was the AudioFire8 and was sold by Echo Audio for something like $750. This is a high quality 8 channel FireWire audio interface typically used for audio recording and mastering. I took mine apart and reinstalled it inside my chassis. A rectangular port is cut into the front of my chassis to access the front of the AudioFire8. I also paid Echo Audio $5000 to write a custom multichannel driver so my device could output surround audio. Since my center channel amp stopped working, I used the AudioFire8's software console to reroute the center channels to the front left and right channels balanced evenly. It's now a working 4.1 system and still sounds great. I can put the AudioFire8 back in its original chassis and sell it for $175. Echo Audio still has drivers on their website that you can download for Windows 7, 8 and 8.1. They are no longer developing audio interfaces and have discontinued further updates so it may not work on Windows 10.

Misc components - A handful of components were included to complete this system. To avoid the loud click that normally happens when you turn on the amps, I added Hypex's softstart module. To connect the AudioFire8 to the amps, there are custom cables with 1/4" TRS connectors. Also included is all the hookup wire between toroids, power supplies, and amps.

UPDATE 2/14/2018: Items that have sold are indicated as such by striking the text. I've listed the remaining items on Craigslist here:

https://madison.craigslist.org/ele/d/diy-amplifier-components/6494593237.html

I've reassembled the Echo Audio AudioFire8 and reduced the price to $100:

https://madison.craigslist.org/msg/d/echo-audio-audiofire8-audio/6494579793.html

I'm also selling an M-Audio FireWire 410 for $75:

https://madison.craigslist.org/msg/d/audio-firewire-410-audio/6494554911.html

AND, I'm selling the 5.1 speaker system that I used to demo my prototype. These are awesome speakers:

https://madison.craigslist.org/ele/d/era-design-5-speaker-system/6476114140.html

USB Audio Class 2.0, Windows and Computer HiFi

One of the reasons we never completed a commercial product was because we didn't have a very good interface between our hardware and the software player. I'm going to explain this in really simple terms, because I don't really want to get into all the technical details.

A device driver, in this case an audio driver, is the software that controls the audio hardware attached to your computer. Our DAC/amp will not function without a driver. The prototype we built long ago, relied on a FireWire driver for operation, meaning our hardware connects to a PC using a FireWire connection. It has a "FireWorks" circuit board, designed by Echo Digital Audio, that supports 8 channels of audio at 24-bit and 192 KHz (the FireWorks can handle many more channels, but we only use 8). Echo uses this board in the AudioFire FireWire audio interfaces they sell to audio engineers. Recording studios use audio editing software like Avid's Pro Tools, Yamaha's Steinberg Cubase, Sony's Vegas/Sound Forge and Roland's Cakewalk Sonar with Echo's FireWire audio interface hardware to provide multiple connections for microphones and musical instruments to record and edit audio. Echo created custom drivers for working in Windows. The audio editing software usually works with Echo's ASIO drivers to get the best performance and Echo also provides a standard WDM (Windows Device Manager) driver so their hardware will also work as a basic soundcard in Windows.

Our product was designed for listening to stereo and multichannel surround sound (I've written several posts explaining how to rip and play multichannel surround audio from DVD-Audio, SACD and Blu-ray discs), not as a recording and mastering device for pro-audio. Unfortunately, Echo's FireWire WDM driver didn't work with popular Windows programs for playing surround, like Windows Media Player or Windows Media Center. If you configured your PC to use Echo's WDM driver, you would get 4 stereo channels instead of an 8-channel device. So we contracted with Echo to update their driver to support an 8-channel WDM device. For those of you using Echo's AudioFire devices with your PCs for listening to surround music or movies, you can thank us for paying for the development of the multichannel driver. Our contract didn't say anything about exclusive use, so now all of Echo's customers benefit from these updated multichannel drivers. You can now choose between stereo mode (which will provide the 4 stereo pairs) or multichannel mode (for an 8-channel setup). Now Windows Media Center can use any FireWorks based product as a multichannel device and you can listen to full surround when you watch TV or play movies and surround audio recordings.

If you were to purchase a device like ours, after connecting it to your PC (via FireWire), you'd have to install the custom driver before you could listen to surround recordings. It wouldn't be plug and play. And, if you get a new operating system, like Windows 8.1, you may need to download an update to remain compatible. So we'd have to continue paying Echo to make sure our device was supported in the case of bug fixes or updates for new operating systems. Also, back when we started this project, FireWire ports were included on most PC motherboards. That's not the case anymore, especially with the smaller form factor PCs that have great potential as HTPCs. Every PC and motherboard has multiple USB ports. So if we were to develop a commercial product, we'd switch to a USB interface and we wouldn't want to depend on a custom or proprietary driver that you'd need to install and keep up to date. Ideally, we'd want an audio device that'd work with drivers that are native to the operating system.

Here's the problem, at least for Windows (including Windows 7 and Windows 8/8.1). All popular operating systems (Windows, Mac OS X and Linux) support USB Audio Class 1.0 natively. Only Mac OS X and Linux support USB Audio Class 2.0 natively. We wanted to sell our product to Windows users because that's where the best apps are for playing high resolution, surround audio and video files. USB Audio Class 1.0 was the standard developed back in 1998 and because of its limited bandwidth only supports 2 channel audio. USB Audio Class 2.0, which became a standard in 2009, has plenty of bandwidth to support multichannel audio. Since Microsoft doesn't have a native USB Audio Class 2.0 driver for Windows, you'd need a proprietary 3rd party driver. We can't afford the licensing fees and we don't want our users to deal with the hassles of installing and maintaining drivers.

Microsoft's Frank Yerrace, who's part of the Windows sound team, asked the WDM driver development community (wdmaudiodev) several years ago why they would want USB Audio 2.0 in Windows. Many responded that they would like USB Audio 2.0 because of support for higher sample rates, bit depth and channel counts.

I agree with David Hoatson, an engineer from Lynx Studio Technology, a manufacturer of pro audio interfaces, who responded:

"now that there are more USB Audio 2.0 solutions coming to market, each company is having to develop its own driver and of course each will have varying degrees of success. Audio driver development is generally not the core competence for a chip-set company so they end up having a 3rd party company develop the driver. OEMs end up with the "not our fault" situation where the chip-set company blames the driver company and the driver company isn't being paid to fix bugs. The end result is products that don't work very well on Windows, but work better on OS X."

David went on to say that he thought the key issue is market acceptance:

"Microsoft never supported audio on FireWire in the OS, and I would say there are fewer FireWire audio devices on the market as a result. If Microsoft supports USB Audio 2.0 in Windows, I think you will see many USB Audio 2.0 devices hit the market." 

A later response from David spoke more to the marketing issues when he wrote:

"I understand the need to convince the upper-level management to get on-board with developing something new. Our VP of Marketing is famous for pushing his "Faster, Cheaper, Better" phrase. I think the phrase applies very well in this instance. Right now the choices for anything more than 16-bit/48kHz are VERY limited. This certainly limits the ability to create a product that will work well with Windows. USB Audio 2.0 does it faster and better, but at the moment it certainly isn't cheaper. If most of the responses were from the pro side, I think that is because we are the people that care about higher quality audio the most... and trickle down does work. Satisfy the top end client and the lower end will thrive filling the low-price-point void.  In other-words, if Microsoft makes the price of entry to the market less expensive to develop, you will see the consumer price-point fill with products.  ("If you build it, they will come"). Besides, do they really want Apple to beat them with USB Audio 2.0? :-)"

Bernt Ronningsbakk, with the Norwegian software company that develops 'Audiolense', responded to Frank Yerrace's post:

"Our customers are basically consumers who are conscious about sound quality. The standard USB implementation is not good for audio. The limitations are not simply about channel count, bit depth and driver problems. It is also about the protocol used to transmit the data. It is basically a S/PDIF-equivalent protocol where the clock on the transmitter (the computer) puts a signature on the sound. S/PDIF is an inferior protocol to begin with. Add to that some added challenges with USB and it stands out as the worst alternative. Some of the jitter out of the PC will manifest itself in the analog waveform regardless of how the receiver side works. A couple of consumer/prosumer manufacturers have developed USB interfaces with asynchronous audio transmission. I don't know the details, but I assume it is equivalent to block processing or callback based buffer filling where the clock in the DAC is the only one that matters. USB has the potential to provide bit perfect transmission. As it is today, a high quality non-USB sound card is required for top quality audio rendering. USB sound cards with multichannel/bit depth capability that reflects the new waveformextensible standards with regards to channel count and bit depth would be a huge selling point to the masses. Callback-based audio streaming would be an added bonus that would bring USB into the picture also amongst those who pay whatever it takes to get the best possible sound quality. Computer based hifi has so much going for it, and a good USB audio solution would lower the threshold of entry significantly."

Like I said, that discussion was several years ago. I think it was around the time Windows 7 was first released and I was very disappointed that Microsoft didn't include native support for USB Audio Class 2.0. We didn't hear anything back from Microsoft or Frank Yerrace. Well actually, Frank did respond to thank everyone for their feedback, but he didn't offer any words of encouragement that would indicate Microsoft was moving toward developing a USB Audio Class 2.0 driver. Following this discussion there were a few people speculating that Microsoft doesn't think there's enough demand to justify the investment needed to develop a driver. Perhaps they are right. I've read a few other forum threads on the same topic and I haven't come across any comments that sound promising. A person (Petter103) who supposedly has close ties to Microsoft offered:

"It would cost Microsoft $50K to have a third party develop this for them (OK let's quadruple that, it is still inexpensive and enabling for consumer scenarios). Until recently, however, Microsoft has not been all that concerned with consumers. It has always been much more important to add 1000 group policy objects per year ..." and, "I have had deep contacts with Microsoft on this very topic for about 8 years now - was pushing very hard for a number of years including walking into program managers and developers offices unannounced. The sad story is that their USB Audio developer who actually contributed to the UAC2 standard quit the company, no idea what is going on now other than hearing through the grapevine that no UAC2 support is forthcoming for Windows 8. My history with Microsoft on this suggests that this will not be a feature of Windows 8, so if it is of interest to you, get yourself a third party driver (not even sure how to do that as a consumer without also buying hardware) with the benefits and caveats that implies, or switch to a platform that offers it. It is sad that this is so, because lack of driver causes fragmentation of driver model (a big third party driver vendor makes the audio driver a non-audio device ....) which in the longer term causes more problems for consumers."

Now that Windows 8 has shipped with no USB Audio Class 2.0 driver, it looks like Petter103 was correct. However, Windows 8 hasn't been very successful and they've had to deal with lots of media reports about its supposed big failures. The market is different now. Not only are Macs more popular than a few years ago, but now Microsoft has to compete with iPads and Android tablets. Windows 8 was suppose to tie together the smartphone, tablet and PC platforms, which you'd think would help keep loyal customers from switching, but that doesn't seem to be working. Maybe Microsoft will pay more attention to their home consumers (not just their corporate customers) and offer better audio capabilities. I was pleasantly surprised to see a new post dated 2/13/2014 from Frank Yerrace on the wdmaudiodev listserv saying:

"I had asked this list several years ago about the level of interest in USB Audio 2 and reasons for the interest. I received some private responses as well as responses to this public list. Even though in-box support ultimately was not included in Windows 8, those responses were greatly appreciated and very helpful. As you can imagine, we are constantly evaluating where to invest for future versions of Windows. I assume the interest in in-box USB Audio 2 support is still quite high. If interest has further increased or perhaps decreased for any reason, please don't hesitate to speak out." 

First to respond was Kevin Halverson, CTO of High Resolution Technologies, LLC., a manufacturer of high quality DACs for consumers. Kevin wrote:

"USB Audio Class 2.0 support is important for a number of reasons. First, the ability to run High Speed USB is becoming a more important issue as the number of new platforms shipped with USB controllers and root hubs which properly support Full Speed USB devices properly diminishes on a nearly daily basis. Second, USB Audio Class 1.0 precludes higher sample rate, high channel count audio which for many companies like ours, means that we have to provide our own USB Audio Class 2.0 drivers. Third, the amount of maintenance necessary to keep custom drivers patched and working well across many different versions of Windows is a considerable challenge. The final point is, we constantly hear from customers that are looking to other host platforms running other operating systems just in order to get native USB Audio Class 2.0 support (and hence why we went to the time and expense of developing our own). While support of Audio Class 1.0 is important to support legacy hardware, it is fairly absurd that all these years later Microsoft still hasn't done what nearly every other operating system supplier has in terms of keeping current with audio requirements. Certainly if a small company such as ours can accomplish this, the task should be rather trivial for an industry powerhouse such as Microsoft."

Again, in this thread there are responses that, depending on your point of view, are pessimistic or realistic. Tim Roberts, a consultant with Providenza & Boekelheide, Inc. and Microsoft Partner, was quick to argue:

"There has to be a business case to justify the considerable development and testing expense. Standards are only interesting if they are used. If USB Audio 2 is a niche standard that is only interesting to a tiny fraction of the market (and the current evidence suggests that is the case), then it doesn't make sense to develop a class driver. To four decimal places, Audio Class 1.0 satisfies 100% of the Windows users in the world." 

To which Timothy Knudtson, a Software Engineer with iConnectivity, replied:

"Where does this number come from? In the audio industry things are moving towards using USB Audio 2.0. USB Audio 1 may work for 100% of the Windows users because for those users who want USB Audio 2.0 they are simply switching to Mac." 

Tim responded:

"The problem is sheer volume. There are a billion Windows machines in the world.  How many really need to use USB Audio 2 devices right now? Maybe 1,000? Maybe 10,000?  999,990,000 out of a billion is 100%, to four significant digits. That's the problem Microsoft faces. They need to make sure all of the corporate secretaries in the world can listen to Michael Bolton through iTunes. 16-channel 192 kHz audio is cool, but there just isn't widespread business demand for it yet."

Jerry Evans, who I believe is a developer with Instrumental Innovations, replied:

"Lack of standards compliance from Microsoft is a barrier for vendors and dissuades consumers from purchasing ‘unsupported’ hardware. Build it and they will come. WASAPI has enabled us to push this project forward. I’m not convinced anyone could have made a business case for its provision. But eventually it arrived, and was quickly supported by all the major DAW’s. Surely a much, much tougher nut to crack than a relatively mundane driver … "

And Philip Gruebele added:

"I think that the lack of standards support is not a strategy that Microsoft can continue pursuing in today's competitive market. It is doing the same thing as the lack of Bluetooth Low Energy support under Windows Phone. The competition (aka Apple & Google) is simply leaving Microsoft behind in this regard."

I thought this response to Frank was very interesting. Børge Strand-Bergesen, who's a hardware guy working on an open source DAC project (Audio Widget Project), had this to say:

"We have an open source Windows UAC2 ASIO driver. Ideally, we'd have a Windows UAC2 driver like the one on Mac and Linux. But since we don't, what I wish to do next is gather enough force to make a fully fledged UAC2 driver and release it under GPL. One centrally distributed device driver with the potential of supporting all UAC2 hardware. The 30-60 demographic has a lot of users who still prefer a PC over a tablet, and who love their music. My doctor is the perfect fit. He loves classical music. After trying a couple different DACs he's ended up with quite the driver collection and resulting DLL version inconsistencies. Now he's in the market for a Mac to play his music, even though he has no other use for one. I have watched the HiEnd audio scene and built DACs for some years now. People borrow and test each other's DACs the whole time. The lack of native UAC2 drivers on Windows is the single largest inhibitor of growth for high resolution audio. Having to install a driver scares away a large chunk of today's customer base, and it prevents that customer base from growing. DLL conflicts and crappy user interfaces push even more users into the Mac camp, where things work out of the box. Getting the promised sample rate in real life is important. Kbps sells just like megapixels. The hardware brand owners also have to struggle with the costly licensing terms of commercial drivers. Those are actually among the largest inhibitors of growth among those who supply to the early adopter users in the DAC market. The demand for UAC2 support on Win7 and onwards does not yet come from Logitech and Sony. It comes from the little guy like me who sells a couple hundred DACs to early adopters. Satisfy those, and HiFi brands like NAD and Rotel will start selling to larger groups. Satisfy those, and the Logitechs will follow. UAC2 support can easily be made a winning sales pitch for Windows PCs. 

In response to Børge, Kevin Halverson, said:

"An open source driver is an interesting idea, but native Windows support for both USB Audio Class 1.0 and 2.0 devices would be infinitely better. While we ship nowhere near the numbers of products as a Logitech and Sony, we do ship +50k units annually and a disproportionate percentage are to Mac and Linux users than one would expect based upon market share of these two platforms. I find it hard to believe that Microsoft's vast resources would even notice the trivial effort necessary to provide a USB Audio Class 2.0 driver (host stack), our small engineering staff accomplished our own in a matter of a few months and that included a lot of research and coming up to speed on what would be well known internally at Microsoft. I really wonder how this could even be something that would have to be considered for more than a moment, it just shouldn't be much of a task. Well, if nothing else. Its getting discussed again."

Here's another person with a good response to Frank's query, from Chris Barker: 

"I've been a lurker on this thread for a while. I'm not actively involved in the industry, but I am an audiophile and been dealing with PC (e.g. Windows) audio for decades. If there is a need to further prove the audience size for improved high bitrate audio support built in Windows, one only has to contact the guys at LH Labs and their very successful Kickstarter and Indiegoo Geek DAC projects. Anything that can improve and make Windows more "plug'n play" and "it just works"  for high quality audio devices would be a good thing for the world in general and users (and thus Microsoft by better perception) in particular. Also check out your favorite consumer audio magazine like Stereophile and The Absolute Sound. Each month's cover always features computer audio articles and now DSD in particular. Many of the writers who are very analog and not computer savvy revert to Mac machines because of the perceived easier experience in getting these systems working. Microsoft should be concerned at this example of quality and ease of use gap."

To counter Chris's enthusiasm, Tim Roberts, the devil's advocate of the group, responded:

"It is really hard to talk about topics like this in an objective and business-oriented way, because the whole arena is filled with so much astrology and incense and pyramids. Physiologically, 384kHz audio is just dumb, as is 192kHz and 96kHz. Anything more than 48kHz is just wasted bits. Sure, a few people are willing to spend money for that kind of equipment -- those are the same people keep telling themselves that tube amplifiers are better. They are buying Macs because Macs are cooler. I'm just not sure that a company like Microsoft can ever have mindshare in that population. Even if they released a USB Audio 2 driver stack tomorrow, I don't think it would be trusted."

So Marc Lindahl of Bowery Engineering, responded:

"Wow, clearly not a pro audio guy. While there is ongoing debate in the professional audio community and the audiophile community regarding 176.4KHz and up, there is little anymore that there is great utility for 96K and 88.2K in addition to generally superior sound quality to 44.1K/48K. The market shows there is a demand for high sample rates and bit depths, Microsoft should be interested in that. It's not 'just a few people'. Windows continues to enjoy popularity among audio pros for running various DAW software, and audiophiles as well.  The market is there."

And Børge wrote:

"I'm sorry Tim, but this is like saying Canon should've stopped adding megapixels once their cameras got 4 or so of them. kHz is a simple number. Comparing the kHz of your audio system will be done in the consumer crowds just like they compared the MHz of their CPUs and the megapixels of their cameras. The more you have of that simple metric, the better they will feel. And at the moment, Microsoft is the audio equivalent of a 3 megapixels camera or a Pentium 4 computer."

 To which Tim replied:

"No, this is not a valid comparison. Our eyes can tell the difference between 300 dpi and 600 dpi, and a 4 MP camera can only do about 200 dpi when printed at 8.5x11. Those extra pixels ARE being put to use. The same is simply not true of audio. You don't "zoom in" on an audio track. The concept doesn't make sense. The best human ears are physically unable to sense frequencies above about 20 kHz. Per Nyquist, anything above twice that frequency serves no purpose at all. They CANNOT, physically, alter what we sense in the sound. That's voodoo, not engineering.  Those MHz and megapixels are being used. Those extra kHz are utterly pointless.  Unlike the other two, we have reached a physical limit."

 Philip Gruebele replied to Tim by writing:

"Three points worth making:

1. Whether or not it is technically necessary to support higher sample rates is not relevant. What is relevant is whether the market demands it, and it undeniably does. Otherwise why would so many companies - hardware manufacturers and download services - invest so many resources to make it happen?
2. Using Nyquist and human hearing to make a case for not supporting higher sample rates is looking at the issue too narrowly. The reason higher sample rates can be better are complex and include things like simplifying DAC design and out-of-band filtering. Also some protocols like DSD64 over DoP require 176.4Khz and DSD128 requires double that just to get the data across. UA2.0 also supports certain use cases which are not possible with UA1.0. The minimum sample rate that should be supported is at least 384Khz and UA2.0 has handled all these cases for many years.
3. The lack of USB Audio 2.0 support causes a headache for consumers because they have to deal with low quality, poorly tested, third party drivers. These drivers are not going away because of point (1). There are a LOT of high-end audio enthusiasts who voted against Windows by using Apple products because they provide a better end-user experience."

There were a few followup responses that went into technical details about the advantages of USB Audio Class 2.0 ver Class 1.0, but what you read above covers the main debate. The last posting was about a week ago on 2/16/2014. I hope these responses to Frank's inquiry will have some effect at Microsoft and convince them to develop a native USB Audio Class 2.0 driver for a future version of Windows. Time will tell. If I hear anything, I'll keep you posted.

External Video Cards?

Everyone knows the advantages of using an external soundcard. The most obvious is the external soundcards have enough space on their chassis for higher quality 1/4" TRS or XLR connectors. This is especially important for recording studios that need to hook up a lot of different microphones or instruments. It's also nice for home theater setups where you have up to 8 channels of high quality audio output. It's kind of a shame to send the signals out tiny little 1/8" connectors, especially when each connector is paired so there are 2 channels per 1/8" connectors. There is also the argument that an external soundcard is going to sound better because none of the PC's components are going to add noise to the analog signal. Oh, and for very small form factor PCs, an external soundcard doesn't take up any valuable internal PCI/PCIe slots.

I just ran across an article in Ars Technica which speculates that we might see external video card solutions in the future. A new PCI Express standard has been approved by the PCI Special Interest Group (PCI-SIG) called the PCI Express External Cabling specification, which will support the development of external video cards. Since the latest and greatest video cards from NVIDIA and ATI/AMD generate a lot of heat, take up to 2 PCIe slots for dual SLI or Crossfire, and need a lot of power, maybe putting them in their own chassis outside the PC might be a good idea. Again, this would obviously work great for small form factor PCs.

What about a combination high performance audio/video box? If we added the necessary space and components to our product, we could have a pretty interesting new A/V product. Something to think about... However, since these video cards generate so much heat, they will need either big heat sinks or noisy fans. That defeats one of the advantages our product has in the market. Which is - our high efficiency amp modules don't generate too much heat, so we don't need massive heat sinks, like similarly powered Class A or A/B amps.

Choosing the DAC, Part 2 -- Narrowing it Down

We're still trying to pick the best DAC (digital to analog converter) for our product. We've looked at all the data sheets and compared the specs and test results. There are hundreds of DACs from several manufacturers to choose from. Using the specs, we were able to identify what we think are the best products on the market. Since we want to support playback of all currently known audio formats (at least those that you can play using an HTPC, which means no SACD because Sony/Philips will not license the necessary hardware and software for playing SACD with a PC), we will need to use a DAC that has a sampling rate of up to 192 kHz and bit depth of at least 24 bits. For our application, we would also like to use DACs with fully differential outputs because of the benefits of eliminating noise from the signal path and the fact that our amp modules work best with a differential input. That narrows our choice down a little bit.

The three key parameters that we looked at for evaluating different DACs were the signal-to-noise ratio (SNR), dynamic range (DR) and total harmonic distortion (THD+N). Based on the three main criteria, we decided to limit our final choice to a DAC with a SNR and DR of at least 120 dB, and a THD+N of at least -100 dB. Here’s a list of DACs that meet our specifications:

Manufacturer	Part #	SNR	DR (dB)	THD+N (dB)
AKM Semiconductor	AK4396	120	120	-100
Cirrus Logic	CS4398	120	120	-107
TI/Burr Brown	PCM1792	132	129	-108
Analog Devices	AD1955	120	120	-110

We've also tried to contact a representative of these highly respected manufacturers, Texas Instruments/Burr Brown, Cirrus Logic, Analog Devices, and AKM Semiconductor, for advice. So far the only ones to respond have been Richard Kulavik, Manager of Marketing and Applications at AKM and John Melanson of Cirrus Logic. TI/Burr Brown, and Analog Devices have yet to respond. Could it be that Amplio is just too small and insignificant? Maybe -- that's one of the challenges and frustrations of being a start-up.

Choosing the DAC, Part 1 -- Basic Theory

When we talk about digital to analog conversion in our application, we are referring to converting PCM (pulse-code modulation) data into an analog signal. This resulting analog signal can either be represented as an electrical voltage or current. So, for a voltage output, a number is the input and a voltage is the output. These numbers are updated at the sampling interval (or sampling rate) of x times per second. For example, CD data is represented with a 16-bit number at a sampling rate of 44,100 times per second. So a 16-bit number, which represents the amplitude of the audio at a point in time is sent to the DAC (digital to analog converter), along with a clock signal, which causes each number to be stored with the correct sequence and timing (lets ignore that relatively important detail for now). Then the output voltage changes very rapidly from the previous value to the value represented by the currently stored number. So basically, the voltage (or current) is set and held in time until the next number is set. What you end up with is a bunch of rectangular pulses that look like the red line shown in the graph below, instead of the smooth gray lines which represent the ideal analog signal.

The differences between the red stair steps and the smooth waveform create a type of distortion in the signal called aliasing. According to good ole Harry Nyquist, the aliasing distortion can be avoided if the sampling frequency is two times greater than the bandwidth of the maximum frequency of your signal. That may not make a lot of sense, so let me use CD audio in another example. Many experts believe the frequency range of human hearing is between 20 and 20,000 Hz. For the majority of us, we can’t hear any sounds above or below that range. So, if you apply the Nyquist sampling theorem (actually Vladimir Kotelnikov and Claude Shannon deserve some mention here, but our friend Harry seems to get all the credit) and double the upper range, we get a sampling rate of 40,000 Hz. So to avoid the aliasing distortion, 44,100 Hz was selected as the sampling frequency for audio CDs.

Open Architecture

In previous posts I've mentioned that we'd really like to design a product that has the modularity and flexibility of the personal computer. Not the closed or proprietary architecture of the Mac, but the open architecture of the PC. Then people could choose the amp modules, power supplies, case, audio interface (soundcard), etc., that would meet their needs for number of channels, sound quality and budget.

From Wikipedia:

"Open architecture is a type of computer architecture that allows users to upgrade their hardware in all of the computer hardware & components (for example the IBM PC had an open architecture). This is the opposite of a closed architecture, where the hardware manufacturer chooses the components, and they are not generally upgradable (for example the Amiga 500 home computer had a closed architecture).

Open architecture allows potential users to see inside all or parts of the architecture without any proprietary constraints. Typically, an open architecture publishes all or parts of its architecture that the developer or integrator wants to share. The open business processes involved with an open architecture may require some license agreements between entities sharing the architecture information."

I'm not sure if we will ever be able to do this, but it is something I am interested in achieving. I think there is great potential here. It may even turn part of the consumer electronics industry upside down or inside out. Of course, this may not appeal to the ultra expensive, high end, "audiophile" producers and consumers, but I think it would really be great for the rest of us.

What do you think? As a consumer, would you like to purchase a system that could be expanded from 2 channels to 8 channels? Or upgrade the DACs or amplifier modules when a new generation is released? Be able to choose from a variety of case manufacturers to have one that best fits your style?

If there are any reps from manufacturers of amplifier modules, power supplies (the best technology for this would be switching power supplies or SMPS), or sound cards reading this, I'd love to hear what you think about this idea? Do you think it would expand your market, or not? Do you think the technical hurdles for designing your components to meet a specific form factor and use of standard connectors would be too limiting? Maybe someone like Creative would offer a version of their X-Fi that would be compatible -- and like the "Intel Inside" promo, they could have "X-Fi" inside. Of course, we could also have "UCD powered", etc.

So, When Will It Ship?

I've been asked several times about the ship date for our product. I don't have an answer for that, but I can tell you about the changes or improvements we need to make to the current prototype before we are ready to ship a commercial product. In this post, I'll give a general overview of improvements needed for each of these subsystems:

1. the chassis
   
2. power supplies
   
3. amplifier modules
   
4. soundcard section
   a. computer interface
   b. drivers/software
   c. digital/analog section - DACs, ADC, etc.
   

I will provide more detailed information about each of these sections in future posts.

As you can see from the prototype photos, the current chassis is not something many people would want in their living or family rooms, unless they're really into the industrial design style. They actually might look kind of cool in an a loft space or something, but that is sooo 90's :). So we need to come up with a more aesthetically pleasing design. We would also like to minimize the size and weight, and allow for optimal heat dissipation. Fortunately, the internal components are relatively small and don't generate too much heat so we should be able to create a chassis that isn't a monster. We'd also really like to design a chassis that would let do-it-yourself (DIY) people build or upgrade their own systems. Much like you can do with PC today. This means the inside of the chassis would include the framing to mount things like power supplies, the printed circuit boards and amp modules. Ideally, the amp modules would simply slide into slots in the back of the chassis.

The main changes we plan to make with the power supplies for our commercial product will be to replace the linear power supplies with switch mode power supplies (SMPS). The latest SMPS technology designed for audio applications is very promising. Compared to general purpose SMPS, the SMPS designed for audio applications usually have much larger capacitors to provide a larger energy reserve for the faster and deeper current demands. General purpose SMPSs are typically designed for fairly constant loads, so they don't usually have large enough capacitance at the outputs for audio applications and adding capacitance to a general purpose SMPS wouldn't work very well because the feedback circuit doesn't take into account this additional capacitance and the added phase shift and oscillation would make it unstable. The main benefit with using the SMPS instead of the linear supplies is since they operate at a much higher frequency, they can be much smaller and lighter than the equivalently powered linear supplies we were using. Since a SMPS recharges its capacitors about 1000 times faster than the rate of a linear power supply, which needs a fairly large transformer and big capacitors to keep up with the current demand, the SMPS can get by with smaller capacitors.

We are pretty pleased with the amplifier modules in the conceptual prototype. The amp modules we've tested are from Hypex Electronics, a Dutch amplifier manufacturer who has developed a very good reputation for high quality products. There are a few things that can be done to optimize these for our application, which will be done if we decide to use their UcD amps in our commercial products. Since we started this business, we have discovered a few other class-D amplifier modules from other manufacturers worth considering. And there is also the possibility of developing our own class-D amp, but unlikely considering the development costs and time. To accommodate our modular chassis design, we would really like to find an amp module that will fit into a small enclosure. This enclosure would be similar to the case of a hard disk drive. It would protect the circuit components, dissipate heat and would allow for an easy method to insert the amp into the back panel of the chassis. If the sizes were standardized, you could upgrade or replace amp modules when newer, better designs were available by simply unplugging the old amp and replacing with the new. We would also be happy to support more than one amplifier manufacturer. Some of the class-D amp modules have a reputation for being very accurate and transparent to the source. These amps sound great, but if the source material isn't very good, like a poor recording, the flaws are pretty noticeable. Other class-D amp modules might be a little more forgiving of these types of recordings. I guess it all depends on your listening preferences. I think it would be nice to have a choice. Now, if only we can find a few manufacturers to work with us on a design for these standard amp cartridges. Wouldn't it be great to have the options of different amp modules just like you currently have with hard drives or video graphics cards?

The soundcard section is where we have the most work ahead of us. The current unit in our conceptual prototype was designed primarily for pro-audio applications - recording and mixing. There are quite a few components that aren't needed in a music playback or home theater system. For example, we don't need 8 balanced inputs if the audio source is the PC. The analog outputs of the pro-audio soundcards are good and usually sound better than your average A/V receiver, but they may not sound quite as good as the high-end dedicated preamp/processors. Their outputs are designed to be good enough for an audio engineer to monitor a mix, but might not meet the needs of someone that is really into critical listening. Our goal is to design a soundcard that sounds as good as some of the high-end dedicated prepros, but at a much lower cost. We've also got a lot of work to do on the software - both the drivers and the control panel applets for controlling things like volume, channel mixing, etc.

Like I said, we'll cover each of these areas in a little more detail in future posts. Please let me know what topics you would like to learn about first.

Connecting to the HTPC

Today most computers communicate with external soundcards using a USB or FireWire connection. Other technologies that might become popular in the future include Audio over Ethernet (AoE) and some new varieties of FireWire like VersaPHY, S800BaseT and POF with IEEE 1394. Our conceptual prototype uses a FireWire connection, which works very well. However, we are looking very closely at other technologies to make sure we provide the best solution for our users.

I also know that some pro-audio external soundcards like M-Audio's Delta 66 and Delta 1010 or Echo Audio's Layla and Gina use a proprietary connection to a dedicated PCI adapter card. Both of these manufacturers are now using either USB or FireWire on all of their newer external soundcard products. We will not be using a proprietary PCI adapter card solution.

USB is the most common method used to connect peripherals to a computer. USB 1.1 was originally meant as a replacement for legacy ports, and a user-friendly, low-cost way to connect peripherals such as keyboards, mice, and printers to a PC. USB was never designed to handle intense multimedia data loads. USB 1.1 is limited to a data rate of only 12Mbits/sec, which is enough bandwidth for CD audio (1.4Mbits/sec). However, it might be difficult for USB 1.1 with it's associated overhead to handle multiple streams of CD audio or DVD-Audio (with 6 channels of 24 bit audio at a sample rate of 96KHz) which requires up to 8.6Mbits/sec. USB 2.0, which is backwards compatible with USB 1.1, provides the fastest data rate currently available at 480Mbits/sec. However, USB uses a host/client (or master/slave) architecture. The PC takes on the role as the host, which requires some overhead to handle all of the arbitration functions and dictate commands to the clients, thus reducing the overall data rates. Data rates are reduced more if addition communication between other clients is required. The maximum length of a USB cable is 5 meters, greater lengths require USB hubs.

Many of the manufacturers of pro-audio soundcards offer an external solution using FireWire (IEEE 1394). FireWire is based on a peer-to-peer technology where each "intelligent" peripheral communicates with each other to provide sustained data rates. Unlike USB, no additional PC overhead (system memory or CPU) is needed to sustain the data rates. FireWire includes support for memory-mapped devices, which allows high-level protocols to run without forcing numerous interrupts and buffer copy operations on host CPUs. The most common FireWire in use today, IEEE-1394a, provides data rates up to 400Mbits/sec with cable lengths limited to 4.5 meters, but up to 16 cables can be daisy chained using an active repeater, external hub or internal hubs included in many FireWire devices. The maximum length possible with any configuration of IEEE-1394a is 72 meters. A newer FireWire standard, IEEE-1394b (sometimes called FireWire-800) provides a data rate of 800Mbits/sec (but promises to support speeds of 1600Mbits/sec. to 3200Mbits/sec. in the future) and cable lengths of 100 meters when using optical fiber or CAT5 cabling. However, if you read the fine print, these longer lengths only support data rates of 100Mbits/sec when using CAT5 cabling. A future version of FireWire, p1394c is suppose to provide data rates of 800Mbits/sec for cable lengths of 100 meters.

Theoretically USB 2.0 should be faster than FireWire IEEE 1394a. Each FireWire device has to negotiate for bus access and the FireWire bus must wait until a given signal has been sent to all devices on the bus. The more devices on the bus the lower the performance. While USB is only limited by the host-client branch, not the whole network. USB's host-client technology also allows the host to allocate more bandwidth to higher priority devices. Even though the USB 2.0 spec of 480Mbits/sec is higher than FireWire's (IEEE 1394a) 400Mbits/sec, the increased CPU and host overhead due to the host/client technology of USB 2.0 reduces its sustained throughput to rates lower than those of IEEE 1394a. USB comes standard on over 90% of computers shipped today (probably more than 90%, now). Unfortunately, FireWire does not come standard with most new PCs. However, I've noticed that it is included on many of the motherboards that are popular with people who build their own HTPCs. Anyhow, both FireWire and USB 2.0 can handle the audio throughput needs of an external soundcard.

Looking into the future, it appears that the performance of USB isn't really going to change much. The only references to a future version of USB talk about wireless USB (WUSB). Wireless USB sounds interesting. You'll get USB 2.0 performance within a range of 3 meters. Between 3 and 10 meters, WUSB can operate at 110Mbit/sec. The future versions of FireWire are even more interesting. I'm not sure exactly what the bandwidth requirements will be for future audio formats like HD-DVD and Blu-Ray (probably, not much more than DVD-Audio's 8.6Mbit/sec, but you never know). And who knows, maybe there will be something better after these two formats kill each other off. Anyhow, the speed improvements of future versions of FireWire might be very useful. What's even more exciting is the fact that the cable lengths will let us support features like whole-house multi-zone audio much easier. With S800BaseT maybe we will be able to have an HTPC in the family room with our soundcard/amp, and others in the kitchen or dining area and bedrooms. All of the PCs are connected via FireWire to either multichannel soundcard/amps or stereo soundcard/amps. They are also connected to each other over the S800BaseT network. Because of the network connection, any of the PCs will be able to recognise all of the other soundcard/amps on the network. That is, your PC will actually have every soundcard on the network in its list of audio devices. With the appropriate software, like J.Rivers Media Center, they'll be able to set up multiple zones. From any one of the PCs you'll be able to pipe music all over the house. For parties, the same tune can play in every zone. However, you will still be able to control each soundcard from the local PC. Hopefully the software will be able to manage when the soundcard is under local control or is available across the network. Anyhow, the possibilities are very exciting since you should be able to connect all FireWire devices up to distances of 100 meters and still maintain S800 (800Mbits/sec) speeds.

After reading several articles or papers describing Audio over Ethernet, I'm not sure if it will ever come into the mainstream. First, there are a lot of proprietary solutions and without a standard, it's unlikely to move beyond its niche. The technology is really geared to professional applications like auditoriums or large recording studios. Second, if S800BaseT takes off, it looks like there will be no need for audio over Ethernet. Anyhow, it is another technology that we will keep an eye on.

I'm sure some people reading this post are wondering why I haven't included HDMI in this discussion. It's because I don't think HDMI (High Definition Multimedia Interface) will ever replace USB or FireWire as a way to connect to external soundcards. Instead, it will probably replace S/PDIF because it is also basically just a one way connection. It is a much higher bandwidth digital connection. Instead of the S/PDIF limits of 2 channel PCM or multichannel Dolby Digital or DTS compressed audio, HDMI can handle 8 channels of uncompressed audio (in addition to all of the HD video). We are considering using an HDMI input instead of/or in addition to S/PDIF as our digital input option. We are already beginning to see HDMI connectors on graphics cards, high resolution displays and A/V receivers. In the next few months HDMI connectors will be included on new motherboards. Another big part of HDMI is content protection and HDCP, but I don't really want to cover that in this blog entry. Maybe some other time.