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发表于 2016-4-29 07:12:31
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这篇评论是十分有价值深度的技术评论，摘自Computeraudiophile。对于硬件构架，软件，外接时钟，文件备份方案，和CAPS对比等都有很有意义的描述。耐心看完开卷有益。
Part 1
Aurender music servers have been part of my digital playback arsenal since 2011. I was so impressed by the Aurender S10 that I placed it on my CASH List and named it the 2011 Product of the Year. The S10 was the first music server I'd seen that was built like a high end audio component with solid engineering on the inside and stellar attention to detail on the outside. The S10 was IT. However, a couple colleagues of mine thought the S10 was a good start, but there was much room for improvement. It turns out my colleagues were correct. Not long after the S10 hit dealer showrooms the Aurender team completed a state of the art listening room and went to work on something better than the S10. The product that emerged from this work was the flagship Aurender W20. The W20 is not an upgraded S10. The only critical component shared by the two models are the oven-controlled crystal oscillators (OCXO). Based on several months of listening, testing, and comparing the W20 to all other servers I've used, I conclude the Aurender W20 is unequivocally the pièce de résistance of high end music servers.
Aurender W20 Hardware - No Hocus-pocus Just Solid Engineering
The Aurender W20 hardware and software were designed by music loving engineers. High end audio hocus-pocus is antithetical to the principles guiding of this team. The state of the art listening room at Aurender's Seoul, Korea headquarters is used to verify engineering changes and concepts implemented in Aurender products. When squeezing out every ounce of electrical and mechanical noise from a product, a very quiet listening room with highly resolving components is a requirement. The Aurender listening room contains analog components from Constellation Audio, digital conversion and clocking from dCS, and loudspeakers from Magico.
Several items separate the Aurender W20 from not only the Aurender S10 but most music servers on the market. At the heart of the W20 design are the main motherboard and physically separated and isolated audio board. Both items were designed in-house by Aurender engineers. When designing a flagship product it's necessary to design one's own audio boards. However, designing one's own computer motherboard is expensive and requires a level of expertise not found at many high end audio companies. A major advantage of designing one's own motherboard is the ability to eliminate or drastically reduce electrical noise. Most commercial motherboards are designed to a very low standard compared to a high end audio component. Commercial board design is often controlled by accountants seeking to lower the price rather than improve quality and features according to Wavelength Audio Founder and "Godfather" of high end USB audio Gordon Rankin. Gordon designed many motherboards for very large computer manufactures before pursuing high end audio. One type of noise caused by computer components when mixed with audio components can be heard easily. For example, I recently received a ~$10,000 audio product for review with built-in WiFi. When the WiFi is enabled but unconfigured a very audible ticking noise can be heard through the right channel. Once the WiFi is configured this noise is reduced greatly but can still be heard with an ear close to the right tweeter. Disabling WiFi on this component eliminates the noise. No such noise can be heard through the Aurender. The moral of the story is, computer components are electrically noisy. The ability of the Aurender team to craft its own motherboard featuring only the capabilities required for audio reproduction and to layout the board for the best electrical performance separates the men from the boys. Powering this motherboard is a high quality switch mode power supply. This supply only powers the motherboard, hard drives, and front panel OLED display.
The W20 audio board is isolated from all other parts of the server by an infrastructure of thick aluminum walls and plates. This board contains a single oven controlled crystal oscillator and high quality parts throughout. Of note is the special USB audio port, dual wire AES/EBU ports, and word clock BNC input. The USB audio port was design to deliver the cleanest possible signal to a USB DAC. (The Aurender W20 has no onboard digital to analog conversion.) Thus, the USB port's location on the audio board rather than the main motherboard. The USB audio signal is buffered, using a proprietary buffering circuit to reduce noise and jitter, prior to transmission to a USBAudio Class 1.0 or 2.0 DAC. The USB audio port's 5V / 1.0A power output can be toggled off and on within the Aurender iPad application. This feature is very nice when connecting to a USB DAC that doesn't require power from a computer such as the Ayre Acoustics QB-9 DSD. There's no sense in sending an unneeded power signal even if it's clean as a whistle. The Aurender W20 runs a custom version of Linux that supports many external USB DACs. There is no user interface to install special device drivers for USB DACs that aren't supported by Aurender's Linux such as those from M2Tech (some not all models) and Mytek. I've tested several USB DACs with the W20 such as the EMM Labs DAC2X, Benchmark DAC2 D, and the Berkeley Audio Design Alpha USB. XMOS based DACs work great for the most part. As a general rule, USB devices that work with Mac OS X without the need to install software / device drivers will work with the Aurender W20. Users with DACs that support other audio interfaces such as AES/EBU, coaxial S/PDIF (RCA & BNC), and optical S/PDIF (TosLink) needn't worry about compatibility with the W20. These interfaces are standards that just work between all devices. More on the AES/EBU interfaces in a bit.
Powering this isolated, both electrically and physically, audio board are two banks of lithium iron phosphate (LiFePO4) DC batteries. These banks alternate charging cycles to eliminate negative performance effects of low batteries. No user intervention is required, the audio board is always powered by these batteries. The audio board is also isolated from annoying ground noise emanating from the mains outlet powering the rest of the server. An additional bank of LiFePO4 batteries is used as a UPS (uninterruptible power supply) when power is removed from the server altogether. This temporary battery supplies the mother board, hard drives, and OLED display enabling the server to shutdown gracefully and inform the user what's happening via front panel display. The W20's batteries are spec'd to last 3,000 charge-recharge cycles until they reach 80% of capacity. If the W20 is used eight hours per day, 365 days per year, the batteries should last about 40 years.
The Aurender W20 features two AES/EBU outputs so it can operate in single or dual mode AES. In the simplest of terms single AES uses one cable and dual AES uses two cables. Both single and dual use digital cables with XLR terminations on each end. This is one major differentiating factor between the W20 and nearly all other music servers on the market. The reason for dual AES on the W20 is that some very high end digital to analog converters from companies such as dCS, Esoteric, and Chord support or require dual AES for sample rates over 96 kHz. The ultra rare and long out of production Pacific Microsonics Model II requires dual AES as well. The Dual AES feature of the W20 is enabled or disabled within the Aurender iPad app. Set it once and forget it.
Along a similar line as dual AES, the W20 supports word clock input. Many of the same DACs from dCS, Esoteric, and Chord support word clock output. Systems from dCS and Esoteric are often configured with a separate master clock component that feeds word clock to a physical disc transport, a DAC, and even an upsampler. This same master clock can feed the Aurender W20 thus all the digital components are fed by a single master clock. Clocking is a big deal in digital audio. The fact that the W20 supports word clock input is another major differentiator between it and the competition.
During the review period I received a dCS Vivaldi system without the physical disc transport. This consisted of the Vivaldi DAC ($34,999), Vivaldi Upsampler ($19,999), and Vivaldi Master Clock ($13,499). Combined with the dCS stack the W20 fits like a glove. dCS and the Aurender team worked together to enable the W20 to communicate with dCS components via RS232. My W20 shipped with a solid aluminum USB to RS232 converter for this communication. Once the dCS Master Clock is connected to the Upsampler, DAC, and Aurender W20 via BNC word clock cables, and the W20 connected to the Master Clock via USB-RS232 the entire system works beautifully without user intervention. Users of dCS will understand what I mean when I say this is a complex system capable of delivering fantastic results. There are other methods of clocking without this W20 - dCS RS232 communication, but the results aren't nearly as good as this preferred setup. For example the DAC could lock on to the incoming audio signal, reading the sample rate as the audio comes into the DAC. Or, a user could manually set the clock on a DAC before switching sample rates. Both of these are less than desirable. The dCS - Aurender communication is terrific.
Another more traditional way of getting excellent sound quality is to send word clock out from a DAC into the W20. This places the clock as close to the DAC as possible (actually in it) as preferred by some manufacturers and listeners. Fortunately none of this "clocking business" is necessary if one doesn't have a component capable of sending word clock to the W20. This should cover 99% of users as most DACs do not feature word clock in or outputs. The W20 is capable of stellar sound quality with or without an external clock feed. When using the W20 with my Alpha DAC Series 2 I simply connected a single AES cable between the Alpha and Aurender. This same configuration was used with the EMM Labs DAC2X in my system. Complexity isn't compulsory for quality. An external clock feeding the W20 should be considered the icing on the cake when used in the correct system.
In addition to working with dCS on DAC / Master Clock communication the Aurender team has worked with both Constellation Audio and Berkeley Audio Design. My W20 also shipped with an RS232 to USB adapter that works with Constellation Audio preamplifiers. Once connected the Aurender iPad application enables control of the Constellation Audio preamp's volume, input selection, and phase. The Aurender iPad app then becomes the only remote needed for daily use of a W20 / Constellation based system. At a CES 2014 dinner my friend, industry veteran, and Aurender dealer Tim Marutani suggested to the Aurender team that they enable USB to infrared control for the forthcoming Berkeley Audio Design Alpha DAC Reference Series. Close to 24 hours later an Alpha DAC was scheduled for delivery to Seoul for testing and the Aurender team had a design for a nice USB to IR adapter in mind. Work on the final implementation of this USB to IR communication is in progress as of the writing of this review. I hope to test this feature when I receive an Alpha DAC RS in the next couple weeks.
The Aurender W20 ships in two configurations. The 6TB (2x3TB) model for $16,800 and an 8TB (2x4TB) model for $17,200. The W20 features an SSD for caching music in the queue enabling the larger spinning drives to wind down. These spinning drives are suspended on rubber and located inside a block of machined aluminum that minimizes vibrations and noise, both electrical and acoustic. The drives are independent, as opposed to combined into a single large drive. The user connecting to a W20 over the network sees both HDD1 and HDD2, each 3TB or 4TB depending on the model. This is one item I wish was user configurable. I prefer to have both drives combined into a single large drive of 6TB or 8TB. This would make copying files easier and space management nonexistent. Currently my W20 has two 3TB drives. I have an A-K folder on HDD1 and both L-Z and DSD folders on HDD2. If my collection music in the A-K folder grows larger than a single disk can hold, I'll need to reconfigure the folder structure. Fortunately, if I create an A-K folder on both HDD1 and HDD2 the Aurender will see these as a single folder when using the folder filter button. This isn't ideal, but it's also not the end of the world or a show stopper. The possible pitfalls of combining both drives into a single larger drive may have to do with adding either hardware or software RAID to the W20 or the fact that losing a single disk would wipe out one's entire music collection rather than half of the collection. Users should worry about losing their music in the event of a drive failure because everyone has a backup, right? If the W20 can be setup for a single large drive I'd love the ability to toggle this on or off from within the iPad application.
Aurender W20 Software - No Hocus-pocus Just Solid Software
The software running on the Aurender W20 is nearly identical to all other models. The only differences are related to support for hardware such as word clock input and dual AES output. The Aurender servers feature Remote Support capability. There are a couple methods of enabling this remote support, one from the actual W20 and the other through the iPad application. Remote support must be enabled by the end user and is only necessary if the user encounters a problem. Once enabled via the iPad app the Aurender team receives an email containing very general system information such as software versions of the system software and the iPad application, and any description of the problem provided by the end user. Upon receiving notification of a problem, initiated by the user, the Aurender team can access the W20 remotely to diagnose and correct issues. This remote access requires no configuration or user intervention other than enabling the feature. I know people who have used this feature in the field and have been very happy with Aurender support. I've used it myself and had great results. The feature seems time limited in that I've enabled it and had to re-enable it because the Aurender team didn't connect immediately. I did't expect immediate assistance as the team doesn't have a 24/7 support staff monitoring and connecting to systems around the world. Not even multi-million dollar computers in enterprise datacenters come with that level of service without hefty service agreements costing tens of thousands of dollars per year. Nonetheless, this remote support feature built into all Aurender servers is very valuable. It's one feature that really separates the Aurender servers from a Mac OS X or Windows based music server maintained by the end user. Another software feature that increases the Aurender value proposition for many users is the ability of the servers to run for months without user intervention required. There are no security vulnerability patches that must be installed immediately and there is no fear of impending doom such as that associated with Microsoft's end of support for Windows XP on April 8, 2014. After this date Microsoft will no longer release updates for Windows XP. There is speculation that malware creators are holding back a barrage of viruses and exploits until Microsoft's support ends. After April 8 it may be game on for hackers and end users may be SOL. On the other hand April 8th may come and go just like Y2K without any major issues for those who have prepared and even those who called the Y2K bluff like Italy and Paraguay back in the day. For some music lovers the thought of updating a music server or even reading about potential issues, however real or benign, is enough to sway them toward a canned server like the W20. The Aurender W20 works like a toaster. When bread is placed in a toaster, the user will have toasted bread in a matter of minutes. Period. When music is placed on the W20, the user will have music at the ready day or night for months on end. Period.
Aurender users without issues or the need for more features can simply keep on keepin' on. Why fix what's not broken? Users in need of features like DSD support can easily upgrade the Aurender software by tapping the upgrade button within the iPad application. When DSDsupport was ready, it was made available for free to all Aurender users. This update included support for DoP version 1.2, DSF and DFF files, sample rates through DSD128 (5.6MHz) via USB output, and rates through DSD64 (2.8MHz) on other outputs. Some DSD fans have ISO images of SACD discs in their collections. The W20 won't play ISO images due to issues with metadata and caching, however the Aurender software has a built-in ISO to DSF converter. Once the ISO image is converted to individual DSD files the ISO image is deleted from the hard drive. Users seeking DSD to PCM conversion for playback through DACs such as the Berkeley Audio Design Alpha series currently need to convert their DSD files to PCM one time before copying them to the W20. The W20 and all Aurender servers support PCM bit depths up through 24 bits and sample rates up through 192 kHz.
The Aurender iPad application is currently the only method of remotely controlling playback. The Aurender team is currently working on an Android version of its application. Testing is being done on the Samsung Galaxy Note Pro 12.2 and a few other tablets. The team has been hesitant to release an Android version due to the fragmentation in the Android market. The number of Android devices with varying levels of performance, screen sizes, and versions of the operating system can be a nightmare for app developers seeking to create the smoothest of end user experiences. At CES this year Harry Lee, creator of Aurender and now Director of parent company TVLogic's SmartAudio Division, was working out details for a power search feature available only on 64 bit iPads. Users with more powerful 64 bit iPads will eventually see this feature while those with lesser capable units will continue using the very good standard search feature.
A number of important items I look for in an iPad application are speed, stability, capability without too much complexity, and a visual aesthetic that serves the end user by increasing functionality.
Speed is critical. Like many users my patience wears thin if an application pauses for a couple seconds between finger taps or has a slow search speed. The Aurender iPad application is very fast. It's search speed is more like an online filter that dwindles down the results as the user types a search term. I've never had to type in an album name or band name and had to tap the actual Search button in order to view results. The results are immediately available as one types. I currently have 4,503 albums consisting of 56,441 tracks stored on the W20. Whether I'm searching albums or the entire database of tracks the search results are immediate as I type. The same cannot be said for most iPad applications in use by high end audio manufacturers.
Stability is critical. Without stability nothing else matters. An app that crashes or doesn't function deterministically will only increase user frustration and possible embarrassment. In high end audio circles there is nothing worse than giving a demonstration to friends or family with equipment that doesn't work. Most of us have been in that situation. "Hey check out my new system. Oh wait, something isn't right. It should be working. I just had it playing music before you arrived, honestly." Official release versions (non-beta) of the Aurender iPad application are rock solid. If a feature decreases stability of the app during beta testing the Aurender team will perfect the feature before release or the team won't release it to the public. Since I started using the Aurender iPad app in 2011, stability has been very good.
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发表于 2016-4-28 18:23:30
