These are exciting times of change in the music world. With CD sales dropping and downloaded MP3 music, streamed music and digital music players taking over there is no consensus for what the future will look like. It could make an audiophile and music lover despair. However, along with all of the change there are positive forces emerging in the market. Numerous sources of High Definition digital audio downloads have emerged on the WEB, great music mastered in high definition audio ranging from traditional CD rates of 16 bits at 44.1 KHz ranging up to 24 bits at 192 KHz are available with several rates in between.

The question at this juncture is not will the computer be used for high performance audio playback but how to get the best from this new music source. I have used the iMac in our main audio system to play back my CD library, download and play high definition music, DVD-A discs, DVD movies, stream radio from around the world, watch streamed television and even play back original live recordings at 24/96. The iMac in my system has over the past 3 years become at least as important as any other source of music, CD player or Turntable and is used daily. This primer will explain an approach that has proven to work well and to provide pointers on what to look for in a quality audio playback system based on a computer.

Critical Issues for Quality Playback of Digital Audio
Most of the issues relating to quality digital audio playback are essentially the same for playback of traditional media such as the CD, SACD or DVD. There are, however, several important differences that will be discussed.

1) Which Computer to Use?
I will primarily focus on the Mac as a preferred platform to store, access and play back quality audio. Some may find this limiting, although given the fact that a Mac Mini can be had for around $600 it seems short sighted to not consider this route, given the advantages over the relative minefield that awaits the PC/Windows user. I personally have had an iMac feeding my audio system and have had no issues related to operation. It is quiet, reliable, I know what to expect when I use it. Indeed it is as reliable an audio source as any CD player or turntable that I have used in the past 30+ years.

2) Ripping your CDs
This is easily done with the Mac systems the quality of the drives and integration of the software and hardware makes ripping music from your CDs into the computer a transparent and reliably efficient operation. Just set the Options within iTunes to insure error correction in ripping of the CDs and the system takes care of the rest. Even damaged CDs that may skip on a very good CD player will be corrected and ripped into the computers hard drive quickly. I would recommend using Apple Lossless to rip your CDs as this does indeed result in a Bit Perfect playback and saves nearly 50% on space. However, given the ever decreasing cost of hard drive space you could save the data in a completely uncompressed format if you wish. With adequate playback hardware to address issues of jitter there is no audible difference in these storage formats. Just be sure to choose and USE a good method for backing up your music library-a RAID type hard drive setup or some other method should be used for backing your library up.

Again the latest Mac operating system has some very useful software to address backups.

Digital Links for Audio Playback
There are several digital links available from the computer to your audio DAC:
In each case the critical issues to pay attention to are:

1) Bit Errors
a. Bit errors are discussed often but are really not a major concern in digital audio playback-uncorrected errors occur rarely and when they are not corrected they are accompanied by silence or clicks and pops quite obvious, if they occur you will know it. Using the correction algorithms within iTunes when ripping my CDs I have found digital errors to be a non-issue, even with CDs that would not play back clean on my CD player.

2) Jitter
a. Jitter is a very critical issue that must be addressed with any audio DAC-no matter if the source is a computer, a CD/SACD player or a DVD player. Any digital link can easily impose levels of jitter that are easily heard in a high dynamic range playback system. At Bel Canto we address jitter right in the DAC with a robust jitter filter that attenuates the jitter components starting below 10Hz, has jitter rejection of 80 dB by 100 Hz and increases even more at higher frequencies. With this filter we can insure jitter free audio playback from all digital sources.

3) Galvanic Isolation
a. Galvanic isolation is when the power and grounds between two components are isolated. This is critical for connecting to a computer as the power and ground system are not clean, first of all, and the ground loops that can occur when connecting a computer to an audio system can create noise levels that severely compromise the dynamic range potential of the system. We engineer galvanic isolation into all digital inputs on our high dynamic range DACs and deem this to be essential for quality playback.

There are several methods for connecting a computer to an audio system.

USB-Universal Serial Bus
USB is a reliable link to get audio date from the computer. It is being used more and more because it works reliably and simply. There are several methods for implementing a USB link. While some claim that superior jitter performance can be had using an Asynchronous method where the critical DAC clock is located on the DAC side of the link this method alone does not insure the best overall operation in the real world.

Asynchronous design is a good approach for jitter but it does leave open other critical issues such as galvanic isolation as discussed above. The USB interface in our high dynamic range DAC products has galvanic isolation built in to insure optimum performance under all system conditions and our jitter filtration insures optimum jitter performance at the DAC clock for USB as well as all of the other digital inputs.

Issues related to the USB interface

• Bandwidth limits using current USB 1.1 links limits operation to 24/96 audio streaming
• No inherent galvanic isolation built in to USB links.
• Maximum wire length of 14.8 feet sets a limit on where you can site your computer. I have used a USB 1.1 compatible optical extender from Opticis to get around this limitation. Bel canto is demonstrating a USB to SPDIF link that uses glass optical fiber for the SPDIF transmission that both provides galvanic isolation and allows running 100s of meters of small diameter, rugged optical cable.
• Future USB links will use USB 2.0 technology. Indeed as of today Mac computers support USB 2.0 operation for multiple 24/192 digital streams!
• Software compatibility: Bel Canto USB links are compatible with the native software drivers in both Mac and PC computers and are therefore transparent to use. They also can achieve bit perfect playback on both Mac and PC platforms.

Firewire
This link has been used for pro audio applications for many years and is well proven. It is typically more expensive than USB but can work well-it has not been as popular for home audio computer playback but certainly can perform well in this application. Galvanic isolation can be achieved within the Firewire standard but it must be designed into the link. There are no real limits to bandwidth for audio streaming with Firewire. Jitter filtration still needs to be designed into the DAC system and Firewire has similar limitation on maximum wire length as USB-about 15 feet.