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High end quality

We truly believe that we can not only have high end playback capability within the 3A concept, but also, further enhance that quality, resulting in better quality that even a high end CD-player can never reach. That sounds rebellious, doesn't it? This deserves some explanation.

How is the music delivered?

First, let's describe how music gets from your CD into your audio set in the 3A implementation. We assume we are using flac for optimal results.

  • Ripping: audio CD is ripped, a file (wav-format) is placed on your hard disk
  • Encoding: ripped wav-file is encoded to a (streamable) lossless audio file (flac-format) placed on the server
  • Streaming: flac file is digitally transported to your Squeezebox by Slimserver
  • Conversion to analog signal: flac file is converted back from digital to analog using a digital/analog converter

Now let's further investigate these individual steps.

Ripping. This copies or extract data from the audio CD into a file on the computer's hard disk. The advantage of CD audio extraction above recording the file using your sound card is that there is no loss of music quality; the data in the resulting wav file is an exact copy of the data on the disc.

Now comes the interesting part: state-of-the-art ripping software can correct defects on CD's better then CD-players! That's because those rippers can reread a track containing errors as many times as needed or configured; each reread pass can give extra information to reconstruct the CD and by that, circumvent the error! Note: such capabilities can only be enabled on CD/DVD players with some special features.

Your CD-player is not capable of rereading a CD multiple times when an error occurs. According to the original CD specification (to which each and every CD-player must ad hire), any CD is only read once, differences between players occur in the way disk faults are solved, or better, masked.

So we end up with a file which is, when there are no defects on the CD exactly the same as the original. If there are defects, the ripping software tries his very best to reconstruct the original information and does a far better job in doing this then a regular, even high end CD player.

Encoding. When we convert the wav file to a lossless flac file, there's again, no information lost. In this context, it's worth to mention that it is possible to reconstruct an original CD from the encoded flac files; this CD is on a bit level equal to the original CD!

Streaming. This is done digitally. It's also buffered to circumvent network anomalies, temporary dips in bandwidth. Slimserver takes care of this process and streams the digital signal to Squeezebox client.

Conversion to analog signal. This is something inevitable. Every digital audio component, ranging from a mp3-player to a (high end) CD-player, must convert from digital to analog. In practice this means that a great deal of audio quality, depends on the quality of the digital/analog converter.

The theory

Let's take the process of music distribution all together:

  • Ripping: no information is lost in ripping, defects on CD's are even better handled than any existing CD-player.
  • Encoding: no information is lost in encoding
  • Streaming: no information is lost in transport from the central server to the Squeezebox client
  • Conversion to analog signal: the digital/analog converter is the component where it's all about!

We can see that not a bit of musical information is lost in the stream, until it reaches Squeezebox and has to be converted from digital to analog. This is our theory:

The audio quality within all components of the 3A implementation solely depends on the quality of the digital/analog converter.

Proving the theory

To be able to test such a theory, this is what we did:

  • set up a high end audio set
  • connect the audio set with a Squeezebox and Slimserver on a laptop
  • connect Squeezebox with of an external digital/analog converter
  • listen to results
  • connect (existing) CD player with the same external digital/analog converter
  • listen to results
  • compare results

As it turns out, we were convinced that the two results we're exactly the same, so that we are actually judging the quality of the external D/A converter only. We proved the following:

The audio quality within all components of the 3A implementation solely depends on the quality of the digital/analog converter.

For a complete test report, see: Squeezebox tested with Entech (blog).

Conclusion and recommendations

You can actually reach high end with the 3A concept. You can go even beyond that when your CD's have defects which the ripping software is able to reconstruct, something even your (high end) CD player isn't capable of.

Just follow these recommendations:

See Technical aspects of ripping for further details on ripping, also known as Digital Audio Extraction or DAE.

Advanced Audio Architecture