Wednesday, September 19, 2007

USB 3.0 Spec Proposed

There was an Intel press release yesterday announcing a group of companies including Intel, HP, Microsoft, NEC, NXP Semiconductor (formerly Philips Semiconductor) and TI have formed the 'USB Promoter Group' to create a superspeed personal USB interconnect that can deliver over 10 times the speed of today's connection. "We don't want to be the bottleneck in the system," said Jeff Ravencraft, an Intel executive overseeing the USB 3.0 initiative.

More from the press release: "USB (Universal Serial Bus) 3.0 will create a backward-compatible standard with the same ease-of-use and plug and play capabilities of previous USB technologies. Targeting over 10x performance increase, the technology will draw from the same architecture of wired USB. In addition, the USB 3.0 specification will be optimized for low power and improved protocol efficiency. USB 3.0 ports and cabling will be designed to enable backward compatibility as well as future-proofing for optical capabilities."

Some people are saying USB 3.0 will finally supplant FireWire. If it really delivers the 300 Mbytes/second or 4 Gbits/second theoretical speeds it obviously leapfrogs the 400 Mbit/second performance of FireWire 1394a and the 800 Mbit/sec for 1394b and 1394c. If the "Quality of Service" support for HD video also results in a very low jitter interface for audio, USB 3.0 is definitely the way to go. The only advantage for FireWire is cable distance. FireWire's 1394c can work over ethernet cable with speeds of 800 Mbit/second up to 100 meters and USB 3.0 may be limited to only 2 meters. However, it might be a long time before we see any audio interfaces that support 1394c. I've also read that the 1394 Trade Association is reading proposals for a 10 Gbit/second FireWire spec. For more detailed information on this, read this article in EETimes.

It will be awhile before we see any USB 3.0 chipsets and drivers for USB Audio, so this probably won't have any impact on our current development efforts. It would be nice if we finally had an interconnect that was very high performance (meaning it could handle up to 24 or more channels of 24bit/192kHz audio with extremely low jitter) and was available on all shipping PCs.

Tuesday, September 18, 2007

LG's Super Blu PC plays Blu-ray, HD DVD and DVD

Korean manufacturer, LG Electronics announced they will start selling a PC that includes their hybrid HD DVD / Blu-ray drive. It looks like it is probably the drive that reads both HD formats and burns DVD and CD. The PC comes with a Core 2 Duo cpu and an NVidia GeForce 8xxx series graphics card. There's no information on the price or availability.

Oh, and you gotta love the models. Kind of reminds me of an American trade show from the '70s.

Monday, September 17, 2007

Modular / Open Architecture Design

I like the fact that you can purchase the building blocks to assemble a PC to your exact specifications. The technically savvy person can buy the chassis, power supply, motherboard, cpu, memory, graphics card, sound card, disk drives, etc., etc., from several different manufacturers and put together a system that costs less or performs better than the pre-assembled systems from the major PC manufacturers. Of course, if you are not technically savvy, you can also purchase a complete system from the hundreds of retailers. Since there are so many PC manufacturers, the prices are very competitive. This is possible because of the open architecture of the PC. I think this might have contributed to the popularity and growth of the PC. On the other hand, Apple's proprietary products may be considered a little higher quality, and that may be due to the fact that Apple has greater control over their supply chain, but they also charge more for their PCs. When you compare market share, the open architecture PC is the clear winner.

Open architecture or modularity might work for an audio system similar to the way it has for PCs. Standard components could be available for the power supply(s), PC audio interface, preamp, amp modules and chassis. The preamp would be similar to a PC's motherboard. This is where the source devices would be selected and routed to the amp modules, plus it could include circuitry for analog volume control. The PC audio interface would have all the functionality of the PC's sound system. It would include the interface to the PC using USB or FireWire, along with the DSP, ADC and DAC chips. An amp module would provide the power for one channel or speaker output. Or maybe some manufacturers could design modules that provide stereo pairs at less cost. Amp modules of different power ratings, like 100W, 200W, 400W, etc. could be available, just like we currently can choose hard drives with different storage capacities. These amp modules could also come with integrated power supplies like the ASP Series from IcePower shown on the left. The chassis could be designed with standard layouts and connectors similar to what is currently available for today's PCs. There might be small cases for 2 channel stereo systems, larger 5.1 or 7.1 surround or even huge tower systems that could house enough channels for a sizable whole house audio system. Someone could choose a very basic chassis with a plastic or painted sheet metal skin and save some money, while others could purchase an expensive thick gauge aluminum chassis with a polished finish.

This open architecture approach has a few serious challenges. To be successful, the components have to be designed with standard connectors and form factors. Just like the hard drive's enclosure is designed with a 3.5" form factor and standard connectors for data and power or a PCI card that fits into the connector on the motherboard, has standard heights and widths and includes the backplate to attach to the back of the chassis. It will probably be difficult to get the component manufacturers to agree on standard connectors and form factors unless they are confident there is a large market for these standardized products. In the early PC days, the IBM architecture was very popular because IBM was a well established, respected company. I don't know of any other manufacturer that could have accomplished this level of standardization and there really isn't anybody in the audio industry with that type of clout today. Besides, most of the manufactures prefer to offer their mostly proprietary solutions.

In addition to the open architecture with standard components, there's also modular design. By this, I mean providing specific components for certain tasks. Separate components for the PC interface, the preamp, amp modules, power supplies, chassis, etc. There's also the separate components you can purchase for your home theaters and sound systems. For example, you can buy a CD and/or DVD transport, D/A processor, preamp, and amplifiers. The specialized components usually sound better, look better and cost a lot more than an integrated solution. Amplio's prototypes have been integrated solutions that include the PC interface, DAC/processor, power supplies, and amp modules all in the same chassis. However, some customers might prefer the flexibility of separate modules. We could provide different products like a preamp that combined the PC interface, DAC, volume control, etc., and amps that can be purchased in mono, stereo or multichannel configurations. Two flavors of preamps might let you choose between a 2 channel or 8 channel solution. The combination of an 8 channel preamp and 3 - 2 channel amp modules plus 1 mono amp module would result in a good 7.1 system. Here's an example of an interesting modular design for PCs called the UNI Computer. Maybe we could do something similar for the preamp and amp modules.

If you have any thoughts or questions about modular and/or open architecture design, I'd love to hear from you. Please feel free to post a comment!

Wednesday, September 12, 2007

The Bad Plus

The Bad Plus are performing in Madison on Friday, September 21st at The Annex.

I can't wait!!

Tuesday, September 11, 2007

Dynamic Range and HD Audio

Recently, I responded to a comment in an AVS Forum thread where someone posted that people shouldn't get too upset if their high definition audio is converted and resampled to 16 bit/48KHz. Apparently PowerDVD, the only PC software capable of playing HD DVD or Blu-ray movies, converts and resamples all of the HD 24bit/96kHz uncompressed or losslessly compressed audio (DTS-HD, Dolby TrueHD, etc.) to 16bit/48kHz. Many people are upset and would like to find a way to play the full resolution HD audio tracks from their HTPCs. The developer of PowerDVD says they have to downsample the audio because the PC doesn't provide a secure pathway for digital or analog output. I can understand why there might be some problems with a secure pathway for digital output without something like HDCP or AACS, but I don't understand why they have to downsample the audio for analog output. Anyhow, he/she basically stated that since the highest frequency a human is capable of hearing is 20,000 Hz, even when applying the Nyquist theorem to 48 kHz, the downsampled audio can still easily reproduce all audible frequencies. Therefore, I think he/she assumed the only advantage to 24bit/96kHz HD audio is the fact they can play higher frequency sounds. Well, there's a lot more to it than that...

My response just touched on the issue of how the resolution of the audio data is related to dynamic range. There are other factors that come into play, like the tonal effects of high frequency harmonics and phase accuracy. There's also the argument that when an analog waveform is converted into digital data, the higher the sampling rate and resolution of the data, the representation of the original analog signal will be much more accurate. There are also concerns about the quality of the resampling algorithm, etc., etc.

Let me get back to the subject of this post - dynamic range. Dynamic range, when used in audio measurements, refers to the difference between the loudest undistorted sound and the quietest passages. In digital audio, the maximum possible dynamic range depends on the bit depth of the audio data.

To calculate the maximum theoretical dynamic range based on a digital audio bit depth, you multiply the log of the total bit depth by 20.

Dynamic Range = 20 * log(bit depth)

For example, CD audio has a bit depth of 16 bits. A bit is a binary unit, so they are actually referring to 2 to the power of 16, which comes to 65536 decimal units. To be more accurate, we would use 65535 because they use values from 0 to 65535.

When we apply this to the formula above, we get:
DR (16 bit CD) = 20 * log(65535) = 96dB

The maximum theoretical dynamic range for 24 bit audio comes to:
DR (24 bit) = 20 * log(16777215) = 144dB

If it is true that some classical music performances can have a dynamic range of over 110 dB, then it's also possible that an HD movie could also have this large of a dynamic range. Hopefully, there will also be some other musical performances (live or studio) that were recorded in HD and become available in HD DVD or Blu-ray that will also have this high of a dynamic range.

My point is, if the audio data is always converted down to 16 bits, we won't be able to enjoy the full dynamic range available from a high definition audio performance.

Test Your Sense of Pitch

From the National Institute on Deafness and other Communication Disorders:

Have you ever wondered how a musician can pick out a single wrong note in a complex piece of music? Has anyone told you that you are tone-deaf or have a tin ear? These all relate to a sense of pitch—roughly speaking, the highness or lowness of a sound. It's what distinguishes a soprano from a bass singer and gives each piano key a distinct identity.

Our ability to distinguish pitch is not fully understood, but we do know that it involves some processing by the brain after a sound is perceived. This means tone deafness is not necessarily linked to any hearing disorder. An individual with perfect hearing may still have trouble distinguishing pitch because of how the brain interprets the sounds.

Research shows that several percent of the U.S. population has problems with pitch perception. Studies in twins also indicates that the role of inheritance in deficits in pitch recognition is extremely high, with little effect of environmental experience. Tone deafness appears to stem from nature, not nurture.

Want to test your own sense of pitch? We've developed an online version of the Distorted Tunes Test, a standardized survey in use for over 50 years. In it, you'll listen to a series of snippets from well-known tunes—some of which have been distorted by changing various notes' pitch. Your task is to pick out the incorrectly played tunes.

Give it a shot. I picked 26 out of the 26 snippets correctly, so I must have a fairly good sense of pitch. Most of the tunes were pretty familiar to me, so it was easy to hear mistakes. The test may not be so easy if you are not familiar with the songs.

Monday, September 10, 2007

Prototype Sketch

OK, so maybe this isn't really a prototype sketch, but I thought it was a pretty cool illustration and that readers of the blog might appreciate it. I came across the drawing on Audio DesignLines article "Amazing Hi-Fi' cartoon/illustration from 1950s". It was drawn by Roy Doty for the April 15th, 1958 issue of Look Magazine. Click on the Audio DesignLine article link to download a copy of the original image.