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Device Sends Music Files Back Home

Looking a bit like an oversize runner's baton, the SoundBridge M1000 from Roku Labs is one of many product designs now available to harmonize the old and new in home audio.

Looking a bit like an oversize runner's baton, the SoundBridge M1000 from Roku Labs is one of many product designs now available to harmonize the old and new in home audio. Like the baton, the M1000 is built for a relay-in this case, of digital PC-based music content to a traditional audio system.

Music input comes via either a wired Ethernet or wireless 802.11b connection with a host PC (or Mac). The M1000 supports playback of WMA-, AAC-, MP3-, AIFF-, WAV- or Rhapsody-encoded files and is compatible with most major music network services. Just plug the audio-out ports of the Roku into the killer stereo of your choice, and all your favorite PC tunes can be heard in a large way. As a bonus, the Roku design can be set up to play Internet radio, in case your personal music list starts to bore.

In any crowded field, it's important to get noticed, and the cool extruded-aluminum tube design of the M1000 certainly stands out vs. the more traditional plastic box. Additionally, a sizable vacuum fluorescent display (VFD) shows a range of highly readable song data, a step up from the smattering of LED status lights found on most designs.

The M1000 is one of three Roku SoundBridge products, and all mix the shared tubular design format with varying sizes and qualities of display. All Roku designs also use two pop-off plastic endcaps that are removed to gain access to all of the system connectors for audio interface and power.

While not particularly cheap compared with plastics, the extruded case allows for convenient built-in capture rails for the slide-in electronics "cage," similar to Apple's iPod Mini. The electronics assembly is composed of a two-piece plastic cage that holds three circuit boards and the Noritake-manufactured VFD assembly. The plastics themselves are sprayed with a conductive paint for harnessing any stray noise generated in the electronics and to keep all those quiet music packages free of external interference.

On the main circuit board, processing horsepower for the M1000 comes from Analog Devices Blackfin DSP (the ADSP-BF531), which does all music decode and runs the user interface, display and system control. Decoding locally with an embedded DSP and streaming only encoded digital music conserves both host CPU and network resources.

The Blackfin DSP is coupled with 16 Mbytes of Integrated Circuit Solutions SDRAM for working memory, 2 Mbytes of STMicroelectronics nonvolatile flash for (updatable) code storage and a smaller, 512-kbyte E2PROM, presumably for boot code or parametric data store.

A Cirrus audio transmitter (CS8405) accepts raw digital audio from the DSP via a three-wire interface and encodes and drives both optical and electrical Sony/Philips Digital Interface ports for connection to the digital audio inputs found on more-recent stereo systems. Just in case the target audio system is a bit long in the tooth, standard audio line-level RCA audio outputs are also provided.

To get encoded digital music into the Roku, a plug-in network interface card (NIC) interfaces with the DSP controller via an Altera EPM3032 600-gate programmable-logic device (For a Related Tech Paper, Click Here). The NIC itself contains a single-chip Realtek RTL8019 Ethernet controller and a Compact Flash socket, which accepts the pluggable 802.11b Wi-Fi card. The Wi-Fi chip set is from Agere. In a departure from most current implementations, baseband and media-access control functions are separate chips, though all radio functions are contained in a single ISM-band transceiver. An amplifier from SiGe Semiconductor, the SE2522L, is used to boost outgoing Wi-Fi signal levels.

A pair of switching regulators from Niko and various data transceivers/buffers for data traffic control round out the major components of the M1000 core electronics. All in all, the Roku reflects a straightforward design, with most of the action centered in a multipurpose, low-cost DSP and off-the-shelf devices elsewhere. A small PLD is the extent of custom logic, reflecting an emphasis on time-to-market and cost control.

At $250 retail, estimated cost of goods for the M1000 is roughly 30 percent of price-a nice margin gained by the premium pricing of high-style products. Whether the Roku fits your budget or tastes is a personal call, but getting the new tunes of the PC into your home audio system-a sometimes sizable investment-is sweet music.

David Carey, president of Portelligent (www.teardown.com). The Austin, Texas, company produces teardown reports and related industry research on wireless, mobile and personal electronics.

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