When it comes to serving music across your home network, you can buy a proprietary server/client system. Or, says Richard Elen, you can serve yourself?free.

Serve Yourself

Richard Elen | Meridian Audio Ltd


by Richard Elen, Meridian Audio Ltd

When it comes to serving music across your home network, you can buy a proprietary server/client system. Or, says Richard Elen, you can serve yourself-free.


Richard Elen is the head of Creative Services at Meridian Audio Ltd, in Huntingdon, Cambridge, UK.

Also in this article:
 Audio File Formats - an overview


Music/media servers that can be used to rip your CDs to a hard drive, and play out your files to your hi-fi system, connecting to your home network to retrieve track information and often album artwork, have been around for several years now. From the beginnings with companies like Escient, several manufacturers are now producing such units - some fairly cheap, others decidedly not so - that are essentially an additional hi-fi component, generally with a CD drive built in or being able to connect to an external one to rip CD content. There are some downsides to this approach, one being that you are actually placing a computer in your hi-fi system and with potentially noisy fans and a hard drive. Another is the fact that such a server is limited to one location. What if you want to listen in the other room? Well, in the absence of a multi-zone hi-fi system, you have to buy another server, and although most such units have the ability to communicate and share content between multiple boxes, this may not be financially appropriate.

So the next step was to create a dedicated server, with network players that talk to it. A proprietary server box goes somewhere in your house - anywhere where you can get at it to pop discs in and where it can be connected to your Ethernet network. Then you have dedicated players that also sit on the internal house network - wired or Wi-Fi -hooking into your audio systems and allowing you to access the server contents. This is today one of the most common approaches to networking your audio (and sometimes multimedia) content around the building from a central source, and it's a very effective one.

But it, too, has downsides. The most obvious one is the lack of integration with all the other storage systems for multimedia - and music in particular - that your house probably has by now. If you have a portable player such as the ubiquitous iPod or its wannabe competitors, you're probably running some kind of program that came with it that allows you to rip your content to disk on your home computer and download it to the player. If you have an iPod, the application that does this is iTunes, which is also a powerful multimedia player for your computer in its own right, and is how it started life. In addition to looking up an Internet database to retrieve track and disc information when you insert a CD, it also, of course, allows you to purchase downloadable songs and listen to them on the computer or download them to the iPod. So the last thing you need, then, is a second place to have to store your disk-based audio files so that you can listen to them on your audio system. And while of course you can plug your iPod into your home audio system, that's not exactly hi-fi.

What you really want is to be able to store all your music in one place - say on your home computer running iTunes - and use the same music storage location (your computer) for everything: listening on the computer itself, downloading to your portable player, and being accessed by networked music players hooked up to your hi-fi system(s).

This is exactly what the Roku SoundBridge is designed to allow. Roku Labs (www.rokulabs.com), based in Palo Alto, California, makes three models of the SoundBridge: the M2000, M1000 and M500. They all have the same playback capabilities: the differences lie in the size of the units and their displays, the M2000, at $400, employing an enormous VFD (Vacuum Fluorescent Display) and the M1000 ($200) a smaller one, while the M500, at $150, uses an LCD. All three units feature extremely elegant cylindrical aluminium housings with black endcaps and a rubber base (you can also wall mount them), and all three feature both Wi-Fi (802.11b, 12Mb/s only at present, via a CompactFlash card supplied) and wired Ethernet capability. Audio out is via a pair of phonos at line level, or digital out (S/PDIF) via coax or TOSlink optical, so the units will plug straight into almost any kind of audio system. There's a compact remote that emulates the functions of, say, iTunes for selecting and playing music.

However, what's really interesting is what they use as a source. To get the full feature set with extended search, info and browsing modes and other features, you simply need to be running iTunes (Macintosh or Windows) or Windows Media Connect (Windows XP). In both cases, the SoundBridge will handle several file formats (see sidebar): with Windows Media Connect it's WMA, including lossless and DRM (purchased) varieties, MP3 and WAV; with iTunes it's AAC (but not DRM), MP3, WAV and AIFF. In addition the Internet radio tuner in iTunes is compatible with the SoundBridge (which can also access Internet radio stations directly: you place their URLs in a list maintained by the unit's built-in web server). This enables the Roku units to offer a great deal of integration with your existing music files, and for that reason I bought one almost as soon as I heard about them.

The Roku boxes also support the Rhapsody service (www.rhapsody.com) on machines running Windows 98 or later; MusicMatch (www.musicmatch.com), for people who play WMA files but aren't running Windows XP; and Twonkyvision's (www.twonkyvision.com) UPnP music server which plays MP3 and WMA files on a variety of operating systems and supports Winamp and iTunes library files. The Roku boxes also partially support the SlimServer music server from Slim Devices, about which a lot more in just a moment, although they don't support it as well as they could (or as well as they used to).

Of course, there is a downside, and that downside is that you now have to leave your computer on all the time, because if iTunes (for example) isn't running on your Macintosh (for example) in the den, you can't play its tracks on the hi-fi in the living room. It is a small step from that to saying to yourself, "Why not simply dedicate a computer to all my music, and leave it running all the time in the cupboard?"

Why not indeed. If you happen to have a slightly older computer lying around that you no longer use, and can hook up a big hard drive (say a couple hundred GB or more) either internally or via FireWire or even USB, you could run a basic operating system on it and run iTunes all the time. Or you could go a lot better and run SlimServer instead - or as well.

SlimServer is a free, open source, multi-platform music server made available by a company called Slim Devices (www.slimdevices.com), based in Mountain View, CA, to power their own SqueezeBox network players, the current incarnation of which is the SqueezeBox 2, starting at $250 (though you can also access SlimServer in a basic way with any MP3-type software player you might have, such as Winamp, or use their own fully-featured free software player, SoftSqueeze). The SqueezeBox does not perhaps look quite as good as the SoundBridge (though the silver ones are pretty cool-looking) but it is a whole lot more versatile. It too has built-in Wi-Fi (802.11g this time, so it can go much faster - a good idea if you are in the habit of streaming uncompressed audio) with a removable antenna, and wired Ethernet; digital coax and optical; and line level analog on phonos. There is also a headphone socket. The unit is smaller than the Roku M1000 but it has an impressive dot-matrix VFD which displays an enormous amount of user-determined information including song details, timing, level and spectrum analysis visualizations and more; and there's a more comprehensive remote, allowing search text entry using the same multiple-keypresses as a cellphone creating a text message, and the creation and selection of playlists etc.

The philosophy behind the Squeezebox is that it contains as little dedicated capability as possible, instead relying on generalized on-board audio DSP (Digital Signal Processing) allowing it to be programmed for different applications which can be developed for it over time without requiring anything more than a firmware upgrade via the Net to provide a raft of new features. These features are driven by the host server software - SlimServer - that runs on more or less any computer you have around: Mac, Windows or Linux. I started by running it on my regular Windows desktop machine, but soon decided to dedicate a machine to all my audio files and installed Linux on an old PC I had available, then ran SlimServer on that. SlimServer does integrate with iTunes - fully, and rather well - and by calling on appropriate resources installed on your computer it can convert more or less any audio file format to something a SqueezeBox can play.

And it can play a lot. The player itself can handle the new lossless formats - where you should, at least in theory, get an exact replica of the original music when you play it - including Apple Lossless, FLAC and WMA Lossless; uncompressed formats AIFF, WAV and PCM; and common compressed formats MP3 (including VBR), AAC, Ogg Vorbis, MP2, Musepack and WMA. The path from server to playback is bit-accurate, so you can, for example, rip a DTS CD to the server (you must use a lossless or uncompressed format for this) and play it back in surround via your DTS decoder fed from one of the SqueezeBox 2 digital outputs.

The SqueezeBox also has the ability to access Internet radio via the server. Plus there is now a new service, called SqueezeNetwork, which is essentially a vast remote SlimServer for Internet radio accessed direct from the player over the Net, with extensive capabilities none of which require you to have a computer of your own running at the time.

The things I can do with a SqueezeBox 2 today are vastly more extensive and advanced than they were when I bought it just a few months ago. The server is updated all the time, though if you are an ordinary user you just perhaps take notice of the occasional significant upgrades. Being free and open source, however, there is massive SlimServer development going on all the time, with a vibrant and incredibly talented community adding and debugging new features on a daily basis, so if you are at all geekily inclined you'll probably be downloading them often to see what new features are on offer - the penalty being that they don't always work very well initially.

So right now I can not only access any file in my music collection via extensive (and I mean extensive) searching or browsing by genre, song, artist, album and more; I can equally listen to any radio program available via the BBC's "Listen Again" service; set an alarm to wake me with whatever I choose; tune in one of thousands of online radio stations (and it stores my Live365 ID so I can access premium streams from the living room); or even read scrolling news services from an RSS screen-saver. And that's just the start. As well as the fundamental features of the server, developers produce plug-ins that extend its capabilities ("AlienBBC" for example is the one that provides me with BBC's "Listen Again").

Meanwhile, you don't even have to drive the system from the remote. You can sit in front of your Squeezebox 2-driven hi-fi system with your laptop in front of you and access the server directly. It has its own web server so you just need to bring up a browser page. Two panes allow you to look at and interact with the server and with a selected player. You can have players around the house and tell them all what to play from your laptop and when, building and editing playlists on the fly, selecting the next track or two based on how well it'll lead on from the current one (you can automate this kind of thing with MusicMagic or particularly MoodLogic, which selects tracks based on mood, rhythm or other characteristics) or even getting boxes to play in sync throughout the house. You can run the server display in 'kiosk' mode so nobody can mess with your server settings, so for example party guests can use it as a jukebox and set up their own playlists (I'm setting up a system like this for a friend who runs a hairdressing salon, so clients can use touch screens to choose music to add to the current playlist). You can select content by album artwork. Crossfade between tracks. Play complete albums, everything by an artist, everything in a genre, everything in your music directory even, shuffled or not.

These are features that the average iTunes user can only dream of - yet you can also use iTunes as a front-end to get music into the system, or any application on any computer on your network that can access your server's audio storage. By opening the appropriate holes in your firewall (and password-protecting your server) you can even run a Squeezebox (or, say, Winamp) at the office and access your own music library. There is also a software version of the player (SoftSqueeze) that can be downloaded via the server and run on a computer when you don't have a hardware player available. And the only thing you pay for is the hardware SqueezeBox itself.

The Roku SoundBridge is also capable of accessing SlimServer by emulating a SqueezeBox, though this is a source of some annoyance at Slim Devices, apparently, because they allegedly simply did it and give no credit to Slim Devices or the SlimServer community for providing the facility. Soon after I bought my SoundBridge I found I was using it in this mode more than anything else, and as a result I bought a SqueezeBox 2 when it came out. I still use the Roku, but the version of the SqueezeBox it emulates is rather old. It'll talk to the latest SlimServer (which thinks it's an old SqueezeBox 1 with a character-based display), but it's been relegated to the bedroom and a pair of small powered speakers. Roku today plays down SlimServer compatibility and apparently doesn't intend to update its SqueezeBox emulator.

The state of this particular market is changing all the time. At present you can have everything from sleek, proprietary servers to cute little boxes powered by an ordinary Mac, Windows or Linux computer somewhere in the building, and as a result you can essentially choose a system more or less on the basis of how involved you want to get with it, and how much you want to be able to do. I would expect the market for dedicated hi-fi and network-connected servers to decrease, while I can imagine a number of hi-fi manufacturers will be incorporating modules to access remote music servers like SlimServer in the near future (Roku Labs offer OEM modules for example). It's an exciting world, and one that's already easy to join.


Audio File Formats - an overview

There is today a plethora of file formats and the "codecs" (encoders/decoders) used to generate them and play them back, in use for storing and handling audio (and sometimes video) information. This just covers formats that you'll commonly encounter in a file serving environment such as those discussed in this article.

You can divide the formats by their exclusivity - proprietary formats like RealAudio, Windows Media and Apple Lossless on the one hand and open-source formats like FLAC and Ogg Vorbis on the other; or you can separate them in terms of their accuracy with regard to the original source.

This means primarily dividing the formats by whether they "lossy" or "lossless" compression, or no compression at all.

The most common format that uses no compression at all, ie it represents the exact pattern of bits on the original source, is WAV (Waveform sound file). This was originally a Windows-based format but it's available on most platforms today. It uncompressed nature means that a CDs worth of tunes occupying, say, 650MB on an audio CD, will take up 650MB as a set of WAV files on your hard drive. Nothing is lost, and no space is saved. The Macintosh equivalent of WAV is AIFF (Audio Interchange File Format), originally developed for exchanging files between digital audio editing and sampling systems: the professional audio industry then, as largely now, preferring the Macintosh platform. You may also encounter PCM (Pulse Code Modulation) files. PCM is the technology used for the vast majority of digital audio recording and playback (thanks to its extreme potential accuracy), where the instantaneous value of the original analog waveform is sampled thousands of times a second and the value stored digitally. Play back an uncompressed file and it should sound exactly like the original.

Lossless compression formats are a relatively recent development. These seek to save storage space while ensuring that nothing is lost in the compression/expansion process. They're equivalent to using Zip or StuffIt to archive files on a computer system: when you UnZip or UnStuff, you get back the original file. The first lossless compression formats were proprietary, notably Meridian Audio's MLP (Meridian Lossless Packing), an advanced compression system used not only in DVD-Audio but also in the emerging high-definition disk formats HD-DVD and Blu-Ray, to allow more audio data to be stored, and for the data to be transferred more rapidly. However, today there are several freely available file formats that are either lossless or have lossless modes. The one that is increasing in popularity is FLAC (Free Lossless Audio Compression). There is also a lossless version of Windows Media Audio and Apple has its own lossless format, Apple Lossless. Play back a losslessly-compressed file and it should sound exactly like the original - it should in fact be bit-accurate, so for example if you rip a DTS CD to FLAC and play it back digitally into a decoder, it should decode (if the player is also bit-accurate, as the SqueezeBox 2 is - see text). Lossless compression systems lead to smaller files and lower data rates than the original files would require. The amount of space or bandwidth saving can depend on the type of material being compressed.

The vast majority of audio formats commonly encountered use Lossy compression. The idea here is that space is saved by removing data that we can't hear - this is known as 'perceptual coding'. The fact is, however, that the more you compress (ie the lower the data rate or bandwidth of the channel, or the smaller the file), the more you can hear the effect of the missing data. Thus the performance of a given lossy compression system can vary from excellent to dreadful depending on the data rate. It also means you can get way more space and data-rate savings than can be offered by a lossless system. At a price. Like lossless compression, however, the amount of space or bandwidth saving can depend on the type of material being compressed. It's also possible to optimise the data rate and compression characteristics of both lossy and losslessly compressed media by using Variable Bit Rate (VBR) rather than Constant Bit Rate (CBR). This means that you use more compression when it's less obvious and less compression when it's more likely to be noticed, as long as you don't exceed the maximum bit-rate of the channel. Some, but not all playback systems can cope with VBR.

The most common lossy format is MP3, which strictly speaking is actually called "MPEG I Level 3". "MPEG" stands for "Motion Picture Experts Group" and many of these technologies were originally developed for digital distribution of movies, such as on DVD. When new formats are developed they are often incorporated into a revised MPEG specification: for example, another lossy format, and rather a good one, AAC (Advanced Audio Coding, the native iPod format) is also known as "MPEG-4 AAC" - it's also the underlying format in Apple's QuickTime. You may also encounter MP2, an earlier MPEG format now used primarily for DAB Digital Radio. MP3Pro is an improved version of MP3, in which the high frequency data, usually the first to sound weird in a lossy system, is preserved. The files can still be played on any MP3 player but reveal higher quality when played back with an MP3Pro-equipped replay system. Ogg Vorbis is an open-source codec often found in Linux environments. Real Audio Media is a proprietary lossy format used by RealAudio players. While formerly very widespread, it is now rather less common and doesn't appear in hardware devices. Some formats, notably WMA and AAC, have special variants that include Digital Rights Management (DRM). You will encounter these on commercial downloading services, and bear in mind that while you will be able to use them to listen to on their appropriate applications (eg iTunes) and download them to approved players, you may not be able to play them via some server software.


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