Squeezebox 3 Digital Music Box

Audio|Video|Misc
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A DIGRESSION, AN INTRODUCTION

Consider me a snob, but until now, I've been happy to let the PC-based music formats pass me by. iPod? MP3? WMA? Bah! No music I've ever heard coming from my PC has interested me for more than a few minutes, even with very nice headphones and a good sound card. All this changed in the past month of my experience with the Squeezebox.

My affair with canned music goes back over 30 years, starting with 7" 45rpm vinyl records, moving through 10" reel-to-reel at 7.5 and 15 ips, high end Nakamichi cassette tape decks, to the golden sunset of the 12" LP in the 80s when high end turntables, tonearms and cartridges enjoyed a prolific flowering.

Today, CDs are the stock and trade of any music lover, audiophile or not. It's been the predominant source of my music for more than a decade. Having been a "Linn-Naim" audio store operator for some years, and still owning a Linn Sondek LP12 turntable + Ekos tonearm combination that gets occasional use, CD, for me, has represented a compromise in sound quality for greater convenience. While there has been a lot of progress in CD technology since its early years, I have not felt compelled to upgrade my CD player given the high cost of high end CD players.

There are two basic tasks for CD players:

  • To read the optical data off the disc and convert it into digital format without errors caused by mistracking, vibrations, laser light reflections, disc imperfections, etc.
  • To convert the digital data into an analog signal suitable for feeding into an amp, preamp or receiver.

Some of you may remember the original slogan for CD dreamed up by Sony and Philips: Perfect sound forever. Maybe some of you believe this to be true, and perhaps $89 CD players are good enough for you, but the emergence of SACD and DVD-Audio, along with the sheer number of high end CD players with 4 and even 5 digit price tags should be enough to cast doubts about perfection. Improvements on perfection don't make sense, and such expensive CD players would not exist if CD players provided perfect music reproduction at the start.

JITTER

Ignoring the second challenge of digital-to-analog conversion for the moment, a whole range of problems associated with digital data extraction from the optical disc can be summed up in a single word: Jitter. Thousands of words have been penned over the years by high end audio writers on the subject of digital jitter. I am neither knowledgeable or interested enough to get into a serious exposition on this topic; any web search should quickly find you lots of answers. Suffice it to say that jitter is related to timing and correct analog signal reconstruction. High jitter causes harshness, especially in mids and highs. The best CD players utilize transports that have been optimized to reduce or eliminate jitter as much as possible. The transport is a large part of the high cost of the high end CD player. The mid-fi CD players that line the displays of mainstream consumer electronics shops lack such quality transports.

What if you could eliminate digital extraction from the optical disk as a source of jitter? You'd have solved half of the CD player's challenge. This is precisely what can be done by "ripping" CDs into digital files with a PC. Just about any CD drive will do, and just about any PC that's less than... say, five years old. Sub-$500 PCs, therefore, can be used. That's much cheaper than even entry level high end CD players, and just a fraction of what the best CD players sell for.

The difference between a CD player designed to play music and a CD ripping software is that the latter applies error correction defined by the CD/ROM standard IEC 10149. Normal music CD players do not use this error correction, which is more complete than that used by music software.

The accepted gold standard for ripping audio CDs is Exact Audio Copy, a free utility created by someone fed up with other audio extraction programs that didn't work as well. It's quite a technical program, with lots of settings that are mysteries to many users, including me. However, there are several good guides on how to use EAC to make "perfect" extractions of music CDs. These include:

Many of these guides get into details of further conversions from WAV to MP3, as well as lossless compressed file formats such as FLAC, which Squeezebox can play directly. For this review, I will cover only lossless formats. WAV files will work fine to start. If you want to save on hard drive space, you can always convert them to FLAC later. A 3-minute song takes up 30 mb in uncompressed WAV format; the 26 CDs I've ripped to 26 folders in the music folder on my computer take up 12 GB. That's an average of 460 Mb per CD. It's a 300 GB drive, which should hold uncompressed WAV files from about 652 CDs. FLAC reduces the files size about 40%, so in lossless format, the maximum number of CDs my drive could hold is about 939 CDs. Given the low cost of storage these days — US$100 will buy you a 200 GB hard drive — the storage cost per CD is barely 20 cents, even in uncompressed WAV files.

Once, you've used EAC on a CD, you have a virtually perfect copy of the original digital file that was the source for the CD. This digital file is free of the imperfections that creep in during the optical extraction process in a typical CD player. But you can use almost any generic CD-ROM drive and PC to create this file, rather than a multi-thousand dollar CD player.

THE PROMISE OF SQUEEZEBOX

This is the basic premise — and promise — of Squeezebox for the computer-literate audiophile:

  • Rip your CDs into WAV files into a networked PC.
  • Install the SlimServer music server software in that PC.
  • Access these WAV files through your wireless computer network with Squeezebox 3.
  • Play them back on your high end stereo conveniently, with high fidelity.
  • If you want fidelity as good as the best high end CD players, use an outboard high end D/A converter.
  • Also access thousands of Internet radio stations, without any computer turned on in the network

Here's the full text of the promotional description for audiophiles from SilmDevices:

What's new for audiophiles? (In Squeezebox 3, according to SilmDevices)

Squeezebox features a high-end design for its audio output stages, which includes components and design aspects usually found only in much more expensive equipment. We listened to our audiophile customers, and carefully designed both the digital and analog output circuitry for extreme performance. We tested many power supply, DAC, and op-amp designs and selected the best configuration using measurements taken with a Dscope Series III audio analyzer. The result is an incredible level of measurable performance rivalling much more expensive equipment.

For the analog output stage, we used extensive power supply isolation and filtering, with separate dedicated linear regulators for the DAC and line-out amplification stages. The PCM1748 DAC comes from Burr-Brown™, a brand widely recognized for high quality and ultra-low distortion levels. Full 6Vpp line-out levels ensure a high signal-to-noise ratio through to the receiver, and power levels compliant with high-end gear.

The S/PDIF interface and DAC clocks are driven directly by two dedicated crystal oscillator circuits running at fixed frequencies. By contrast, other low-cost devices generally use a PLL circuit or resampling techniques to simulate multiple clock frequencies - these designs are less expensive, but they introduce noise or are more susceptible to instability due to power supply noise and environmental factors. By using dedicated fixed oscillators, Squeezebox eliminates the predominant source of resampling noise, jitter, and clock imprecision in S/PDIF sources.

In addition to this new hardware, Squeezebox uses a new signal processing architecture implemented entirely in software - we call it SlimDSP™. This means that all audio format decoding, synthesis, filtering, mixing, and attenuation operations are tuneable and upgradeable with firmware. Even all of the audio-releated logic circuitry, such as the encoding of the S/PDIF output signal and the presentation of data to the DAC, are implemented in a field-upgradeable Xilinx gate array. Squeezebox is without a doubt the most capable, configurable, and upgradeable networked audio device ever created.



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