Achieving bit perfect playback with zero interference is the goal, right? I will use this post to explore my findings with computer based stereo systems. Here’s some of the equipment I tested out.
For this test I used an Apple Macbook Pro for my audio playback system. The Macbook Pro supposedly has better RFI (radio frequency interference) rejection than the Mac Mini. PC’s are also possible playback computers, but this article will relay my Macbook pro experiences.
Building a Hi Fidelity computer based audio server/player can often present some challenges. While iTunes organizes music well, it doesn’t play it back with the highest fidelity. Enter the software developer. In recent years we have seen a variety of playback software come onto the audiophile market. This software, such as Pure Music** and Amarra allows iTunes to open and be used as a GUI while pure music handles all the audio processing. Features like RAM memory playback, upsampling, and turning off handshaking allows digital music to be reproduced with less artifacts/jitter.
Computers are notorious for producing noise. Not only do the fans make acoustic noise, but also the graphics card, processors, and other components produce power line noise. This hash is transmitted down USB, Firewire, and other ports that transmit DC power. The sensitive clocks that produce the sample rate in these USB/Firewire DACs are affected by the noise transmitted down the busses DC leg.
The German-made Yellowtec Puc 2* USB audio interface converts USB to AES for the Crane Song Avocet DAC. Providing clean power to the USB powered AES interface is of utmost importance. In order to tackle this issue I first start by separating the digital and analog audio gear. Shunyata hydra 2 units are used for this purpose. The DAC/Monitor controller gets AC power from one hydra 2, while the stereo amp is plugged into the other Hydra 2. If I had the ability, I would place each of the Hydras on their own dedicated AC circuit. Furthermore, I have the computer on a separate circuit with a surge protector.
Other products exist from companies like AQVOX that allow you to lift the DC power from the computer and insert a separate power supply for your USB device.
I will continue to relay my findings as I explore this topic more. Stay tuned…
The Yellowtec sounds best when operating on internal clock, as do many converters. The Puc 2 also benefits from clean power via the previously mentioned methods.
*The Yellowtec Puc2 is asyncronous and can be locked to an external word clock via AES-3 connection. The Benchmark ADC-1 was tested and provided rock solid clock to the Yellowtec Puc 2. Rock solid when locked to 44.1 and 88.2 via AES-3 signal from ADC-1. At higher sample rates, the Puc2 seems to prefer its internal clock.
**Pure Music sounded best when used in 64 bit mode and power of two upsampling enabled. For redbook CDs that were 44.1 SR, upsampling to 88.2 via Pure Music provided the best sound. The 88.2Khz Clock was provided via the Yellowtec Puc2. DSP functions on Pure Music “off” except for upsampling/meters off and in “Less is More” mode.
*** All USB ports on the macbook and mac mini are not created equal. Some of the ports share other busses such as isight, IR, and bluetooth. You can also disable the IR receiver in system preferences.
A usb cable that separates the DC power leg from the data wires with spacing and shielding is recommended. I use a Wireworld usb cable with this key design feature.