The Apple Airport Express (AE) is a beautiful device. One of its functions is the ability to act as audio Airplay receiver. Airplay is a streaming protocol, based on a lossless 44.1KHz/16 bit stereo audio stream. It’s part of iTunes since a long time. It uses Bonjour for service advertisement and as such is zero conf. My AE is the 2nd gen model with 802.11n (update: The A1264 model). All models have a combined analog optical output. Many years ago I used it with an Apogee Minidac and the results were very good. One year ago I connected everything again and was disappointed with the
The Apogee MiniDAC is a wonderful converter. But how does it work? Well, first of all, you can’t download the schematics from the net. So how it exactly works I don’t know. But looking at the components inside reveals at least some info. Therefor my guess is as follows: 1. Two times CS8416 input digital receiver/PLL chip. Looking at the number of inputs and print layout, I guess the two units are needed because of the number of inputs to be switched. 2. Wavefront AL1402, that’s an ADAT receiver chip which decodes the 8 channel (optical) ADAT stream into 4 stereo pairs. 3. Xilink Spartan XC2S50
The Apogee MiniDAC is a pro-audio two channel digital analog converter. It received very good reviews when it was first introduced. The price dropped after a few years, making it good value for money. I managed to get hold of one and of the firewire interface board a little later. The firewire board is a BridgeCo design, running an ARM processor. The firewire interface deploys a smart architecture where multiple firewire units can be used together with one unit delivering the master clock to all other units. Due to the firewire architecture the computer’s driver can also be the master. The Apogee driver on OSX
With perfectionist audio, a perfect digital chain is often described as “bit-perfect”. When two player applications are both bit-perfect; there should be no audible difference between them (when the rest of the chain remains unchanged of course). People now realize this is wrong; they hear differences between players such as Amarra, Decibel and Itunes. Actually this observation is not heavily discussed; most people can hear it. So clearly bit-perfect alone is not enough to describe the quality of a digital audio player. When describing a DAC; bit-perfect is not a point of discussion, however another parameter called ‘jitter’ is (check wiki for background on jitter).