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 results. Of course, your first thoughts are something like: “I forgot that it sounded so bad”, or “this optical cable is bad” or whatever. So I dismantled everything..

A few days ago I hooked it up again, now connected to my brand new SMSL M8 DAC. What a surprise: dropouts, dropouts! WTF, this is not happening (why me..) Time to Google. Of course this has nothing to do with: my WiFi network, the optical cable, my neighbors etc. etc. Then I found this post about dropouts starting after a certain firmware upgrade. I never thought about that one. (this is always a sign that you are on the right track in solving a problem). Time to try it out.

Downgrading firmware on the AE is surprisingly simple. Use the magic ALT button in the Airport Utility program to show hidden functions and select some older firmware version, in this case 7.6.1. Reboot, listen. WTF again: not only are the dropouts gone (completely!!) but the good old sound quality is back. Time to reflect.

The dropout are caused by very bad clock (SP/DIF) behavior. So bad, that the M8 DAC cannot keep track. Why this is caused by the new firmware, only Apple knows. My guess is that the addition of more features in newer firmware pushed the CPU to its limits. The Apogee Minidac was able the handle the bad clock without dropouts, but bad timing makes bad audio…

4 Comments

  1. Many, many thanks for this! I’ve been trying most of the day to get my AE to speak coherently to a SMSL Q5 without stuttering,
    and this is was the secret! On my airport utility I had to hold down the option key over the firmware version number and this
    allowed me to revert to 7.6.1 and now with my cheap mini plug to toslink cable things are finally working.

  2. Hi Frank,
    I have also an Airport express model 2, but I cannot roll back to 7.6.1. I only can go to 7.6.2. and I really waanted to use its optical output to enter my smsl AD18 (a good FDA).

    One request if I may : can you look in ~/Library/Application Support/Apple/AirPort/Firmware to open the version.xml file (it is the file that records the http links to the different firmware that you install for your device). If you find a block like this (with productID some number between 107 and 116, ideally 115, the weblink would be exactly what I need

    location
    http://apsu.apple.com/data/*****/7.6.1.basebinary
    productID
    ***some number between 107 and 116 ideally 115***
    sizeInBytes
    ***
    sourceVersion
    ***
    version
    7.6.1

    Best

    Pierre

  3. Sorry to say, this didn’t work for me, but I did learn something from the article.

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