I recently started building my own MythTV system, for reasons that are detailed elsewhere. Even though the broadcast flag was struck down on May 6, I nevertheless pressed ahead with building my system because I was sure the broadcast flag would be back. Although the Innovation Coalition won round one, it was only the opening skirmish. Sure enough, it rose from the dead, rather like a vampire, on Monday. The only sure-fire way to keep my right to tinker with TV was to beat the original deadline.
The court decision states that the FCC lacks authority to impose the broadcast flag because Congress has not enacted law giving it that authority. One week after the court ruling, Declan McCullagh reported that the MPAA has submitted draft legislation that would give the FCC the power to enact the broadcast flag. Round 1 went to the coalition to retain current rights to time-shifting, but the battle is far from over.
For now, the good news is that it is still legal to put together your own home-theater PC. Parts are now cheap enough that it is no longer ridiculous to build a PC specifically to handle TV for you, much like the VCR in Douglas Adams's Dirk Gently's Holistic Detective Agency ("Take the VCR, for example. Not only can it watch TV for you, it can watch more channels and watch them better than you can."). As home theater PCs have become far more common, the resources available to those of us building them are much more detailed. Unlike most review sites, Silent PC Review focuses solely on the noise generated by system components.
Before I could get MythTV running, I needed a computer. By temperament and experience, I am a software hacker. If something fails, you reinstall and start over. With hardware, though, you are stuck with your mistake until you pay money to correct it. After a great deal of research, I decided on the following parts:
This one is easy. The HD-3000 from pcHDTV is one of only two capture cards for Linux, and the direct descendant of what was once the only card available. I purchased multiple cards so that I could build a multiple-tuner system. Furthermore, Jack Kelliher, the founder and CEO of the company, is deeply committed to open source software's role in television.
The case you pick depends in part on the system architecture. MythTV can be split into a front-end that displays video streamed from a back-end responsible for scheduling and recording. The back-end can record several things at once, and be on a powerful (read "noisy") server stashed away in its own room. My home does not really have a room I can use to isolate noisy machines, so I chose to build an all-in-one system that handles both the front and back ends.
For the foreseeable future, I plan to keep my life relatively simple by relying on digital TV received over the air. The back-end resource requirement for a system that only receives digital TV is not taxing at all. Digital TV is already digitized for your convenience, so all that the recorder needs to do is to save the bit stream from the airwaves onto the disk.
Having chosen the capture card, I needed to buy a case that could accommodate two of them. The HD-3000 is a full height card, and requires a case that supports full-height cards. My initial case choice, an Ahanix case, supported only low-profile cards.
Other compact systems use a PCI riser to support full-size cards, but the smaller form factor limits the number of available slots. I eventually decided on a Silverstone LC03V, which has a small vacuum fluorescent display. I was also drawn to the Silverstone LC10M, which is a similar size, but has a display integrated with an infrared receiver. In a concession to aesthetics, I decided to go with the LC03V, which looks slightly less like a PC box.
The power supply is potentially a big source of noise. Silent PC Review's recommended power supply list was invaluable advice. The key points I took from the review are that efficiency matters a great deal for noise reduction, and that you don't need to buy the biggest power supply you can get your hands on. The highest rankings on SPCR went to Seasonic power supplies. After adding up many of the other components, I went with the S12-330, the smallest model in the line-up. It has power connectors for just about any device you could hope to use, including multiple Serial ATA power connectors.
In a home theater PC, you need to keep the system as quiet as possible. Much of the noise comes from cooling the system. More heat means more fans. Chip vendors will quote a "thermal design power," which is the amount of heat generated at maximum load.
Intel's high-end Prescott core has high clock speeds, but a frightening cooling requirement. The EFF's cookbook recommends an Intel P4 of at least 3 GHz. While it will work, the P4-3.6 has a thermal design power of 115 watts, with a maximum power draw of 141 watts. Yikes!
I took a slightly different approach, and looked at the relatively recent 90 nm CPUs, with much lower heat generation capabilities. Intel's Dothan core, used in the Pentium M processor, is simply astounding, with a thermal design power of between 3 and 21 watts. AMD's Winchester core ranges from 21 to 67 watts.
Either of them can be put in a system that runs far, far quieter than a Prescott core simply because you will not need to devote so much noise to cooling. AMD's Venice core, which is also a 90 nm process, runs slightly cooler than a Winchester core at the same clock speed, but it does cost slightly more than a Winchester core at the same clock speed.
I investigated the cost of a CPU, motherboard, and video combination, and found that an AMD system was significantly cheaper. All the desktop motherboards that support the Intel Pentium M require the use of pricey PCI-Express video cards, while desktop motherboards that support socket 939 AMD CPUs have AGP slots. Furthermore, the AMD motherboards are available as full-size ATX motherboards, leaving extra PCI slots free for future expansion. AMD motherboards were also significantly cheaper.
It was clear that for cost reasons I was buying an Athlon64. When the dust settled, I chose a 2 GHz Winchester core (AMD Athlon64 3200+) because it was slightly cheaper than the 2 GHz Venice core.
The LC03V takes either a full ATX or micro ATX board. With a multiple-tuner box, I wanted as many slots as I could get. Two slots are already spoken for--they have to hold the tuner cards. Beyond the tuner cards, though, it is conceivable that I may someday want additional capture cards for other video sources, or improved network connectivity, or even improved sound handling.
In the immediate term, I wanted to ensure that I had disk space expansion capabilities. Most Socket 939 motherboards have two SATA ports, but I wanted as many as I could get for future expansion. That, along with a desire for external FireWire connectivity, led me to the MSI K8N-Neo2 Platinum board.
For a MythTV box, this is easy. nVidia graphics cards have MPEG-2 acceleration useful for playback, and are well supported by the Linux drivers. There is no need to get a bleeding-edge card. Any GeForce4 MX or later card has the acceleration built in. For noise reasons, the older cards are often better because they have heatsinks rather than fans for cooling. I selected a Gigabyte card based on the GeForce FX5200 chipset because it has DVI output as well as an S-Video/Composite output port. Unlike many other cards with an S-Video port, the Gigabyte card includes a short S-Video to composite dongle cable.
One of the advantages of building my own device is that some day, I can plan to archive recordings to DVD. I decided to go with a dual-layer device so that I could avoid obsolescence as dual-layer disks become more common. Although I wanted a serial ATA drive, they were substantially more expensive than the IDE versions. The only other selection criterion was to get a black drive to match my case. I ended up buying a Toshiba SD-R5372.
The motherboard and CPU support using dual-channel memory, so I purchased a kit consisting of two memory modules. Based on the small cost difference between 512 MB and 1 GB, I decided to go with 1 GB. Vendor selection on memory is often as much religious as technical. I am a member of the Kingston sect because the one time I have needed to redeem their lifetime warranty, they made the process quick and painless.
After fighting with routing airflow-blocking IDE cables for all these years, Serial ATA was the clear choice for me. Samsung SpinPoint hard disk drives are highly recommended by Silent PC Review. In a fit of pointless cost saving, I only bought a 120 GB drive; a 160 GB drive would have cost only $10 more. The drive has been perfect. Even under high disk loads, no hard disk whine is audible outside the case.
Although all the video applications you can run have keyboard commands, it is much easier to use a remote control. Different applications have different keyboard shortcuts, so it helps greatly to unify the control system. The Linux Infrared Control (LIRC) project supports most IR receivers. In an interesting twist, LIRC can be programmed to work with your existing remotes. Most people buy universal remote controls and program them to operate with their existing hardware. Using LIRC, you are buying a universal receiver and programming it to work with the remote controls you already have.
There are two types of receivers commonly used with LIRC. Schematics for simple home-brew receivers are on the LIRC page, but several companies sell commercial solutions if your days of soldering competence are just a memory (as mine are). Several people sell professionally-made home-brew devices as well. The home-brew devices have one notable drawback, though. Each of them requires constant attention from the CPU to process received codes. I chose to use a microcontroller-based receiver instead, which only needs to interrupt the CPU when commands have been received.
Microcontroller-based devices come in two flavors: RS-232-based and USB-based. USB commands a large price premium, so I bought a serial port-based IRA-3 from Home Electronics.
I am still in the process of ironing out various software kinks, and I have not yet received the infrared receiver. The system is assembled; see Figure 1 for a picture of the inside of the case as built. Although the system is running, I am still using my TiVo in parallel until I get the kinks worked out.
Figure 1. The inside of the case.
I am completely satisfied with the AMD processor. It was far, far cheaper than the Intel processor, and handles the computation load without a sweat. On playback of HD streams without using any acceleration features of the video card, it requires approximately 40-55 percent of the processor.
That may seem excessive, but the motherboard and operating system keep the processor operating at its lowest possible speed. Even while taxed playing back an HD stream, the speed only occasionally rises above the slowest operational speed of 1 GHz. Recording two video streams requires only 3-5 percent of the CPU for the back-end process. My only complaint with the processor is that the fan included with the boxed-set model I purchased is one of the largest noise sources of the system.
The case is satisfactory, though I have some additional future work to quiet it down. It is larger than I would have hoped, and hard to put in the entertainment center. When I selected the case, it was hard to tell whether the fluorescent display was supported on Linux.
As it turns out, it is completely supported, though it was time-consuming to sort through the options and find the magic configuration incantation. The case itself is quite striking, with a high-polish finish that I can practically use as a mirror. (The downside is that I am now all too painfully aware how much dust floats through the air at home.) My only complaint with the case is that the optional 80 mm Silverstone fan sold as an accessory to cooling the drive bay (FN-81) is so noisy as to be unusable. The two 60 mm fans in the back panel shown in Figure 2 could stand to be quieter.
Figure 2. The 60 mm fans.
The power supply is an unqualified success. The interior-facing side of the power supply has a large 120 mm fan, and the power supply is able to dissipate most of its generated heat without requiring a high fan speed.
Figure 2, taken from the front corner of the system looking towards the back, shows the large size of the power supply fan in relation to the case fans. Seasonic has designed a highly functional power supply that is smart enough to keep its fan idle when the cooling power is not needed. Large internal heat sinks are able to radiate most of the load without requiring the power supply fan.
As the weather gets warmer, it should be interesting to see whether the power supply fan is ever needed. As an added bonus, the power supply is also thoughtfully bundled with a cable management kit, which did a great deal to keep the inside of my system relatively neat. The split tube that runs from the back of the system to the front was included with the power supply, and I used several included zip ties to keep excess cable looped up nicely.
I am quite happy with the IR receiver. I chose to buy an external receiver so that I could position the receiver on top of the TV, regardless of the PC's position in my home theater cabinet. The IRA-3 uses an RJ-45 port, so any future extension cables will be easy to make. The receiver itself has good sensitivity, even in bright sunlight, and has a wider range of operation than my TV's built-in remote control eye. Eventually, I plan to program my universal remote to control the whole setup, but for now, I am using the DVR2 position on my TiVo remote to control the Myth system. Getting LIRC running was a bit challenging, though the problems I encountered were for the most part unrelated to the IRA-3. I needed to compile from scratch to adjust one parameter in libirman, and the LIRC software has not proven to be completely stable.
My only disappointment so far is the motherboard. My biggest mistake when selecting the motherboard was not paying attention to the pictures. The north bridge on the MSI has its own fan, which is quite loud. An early modification project will be to replace the north bridge cooling fan with a heat sink. The main reason why the bridge has its own fan is to make room for longer PCI cards, but I do not need the length. The tuner cards are quite short, and will co-exist with a high heat sink, as can be seen in Figure 3, which looks from the front of the case over the north bridge to the rear.
Although the motherboard supports AMD's Cool'n'Quiet technology, a second annoyance is that it lacks a motherboard fan sensor to control the speed of the case fans. The case fans tend to run at a high fixed speed because there is no sensor to throttle them back. I am also investigating whether I can use the soon-to-be disused north bridge fan connector as a fan sensor. That would drive the case fans in response to the temperature of the north bridge chip, but that may not be entirely inappropriate if the north bridge is passively cooled.
Figure 3. View from the front to the rear.
The built-in sound system on the motherboard has been a recurring source of trouble. One of the San Francisco-area PBS stations broadcasts five subchannels on their digital station, but anything I record on any of the subchannels has audio that stutters badly. The problem appears to be with the audio playback, but I am still diagnosing it. I certainly hope that it does not require investment in an additional sound card.
This article is the first in a series of my project, with more to come as it progresses.
Matthew Gast is the director of product management at Aerohive Networks responsible for the software that powers Aerohive's networking devices.
Return to digitalmedia.oreilly.com