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Does airport express support ethernet input?

I currently use ethernet to connect my MacBook Pro to an older AppleTV. I use the optical out from the AppleTV as input to my DAC. This allows me to feed output from iTunes to my stereo system. I have to use ethernet because my wireless signal is too weak at the stereo.


This works fine but I have been told the AppleTV only supports 44.1/16 while I can get 96/24 or higher out of my MBP and my DAC. This makes the AppleTV a bottleneck.


It has been suggested that the airport express can accomplish the same thing and can handle any sample rate and word length. However, it is not clear from the web site that the ethernet port can be used as an input. Can it?


I propose to connect the MBP via ethernet to the airport express and use the optical output from the airport express as input to my DAC.


Before you bring it up, I cannot use the optical out on the MBP because I already use that output to feed a small analog desktop system.

Posted on Jun 30, 2011 8:22 PM

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Posted on Jun 30, 2011 9:20 PM

It has been suggested that the airport express can accomplish the same thing and can handle any sample rate and word length.


Sorry, but that is not quite correct. The AirPort Express Base Station (AX) is basically limited to audio files that iTunes can read; i.e., 16-bit data only. These data, though, can be in any file format that iTunes recognizes, from lossy MP3s at the low-quality end of the spectrum to Apple Lossless, AIF or WAV files at the high end. The AX functions only at a 44.1 kHz sample rate. If you play a 48 or 96 kHz data, iTunes sample-rate converts the data in real time before sending via AirTunes/AirPlay to the AX.


For digital audio, the AX is a pass-thru device, but uses an internal DAC for analog output.


The AX Ethernet port can be both an "in" or "out" port, depending on its configuration. AirTunes/AirPlay streams can be sent to the AX either by wire or wireless.

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Jun 30, 2011 9:20 PM in response to IHaveOne

It has been suggested that the airport express can accomplish the same thing and can handle any sample rate and word length.


Sorry, but that is not quite correct. The AirPort Express Base Station (AX) is basically limited to audio files that iTunes can read; i.e., 16-bit data only. These data, though, can be in any file format that iTunes recognizes, from lossy MP3s at the low-quality end of the spectrum to Apple Lossless, AIF or WAV files at the high end. The AX functions only at a 44.1 kHz sample rate. If you play a 48 or 96 kHz data, iTunes sample-rate converts the data in real time before sending via AirTunes/AirPlay to the AX.


For digital audio, the AX is a pass-thru device, but uses an internal DAC for analog output.


The AX Ethernet port can be both an "in" or "out" port, depending on its configuration. AirTunes/AirPlay streams can be sent to the AX either by wire or wireless.

Jul 1, 2011 6:13 AM in response to Tesserax

Thanks for the input on the ethernet port. That is one big concern solved.


The sampling rate answer is more confusing than helpful. First of all, I am talking optical only. I want to stream music from my MBP to my DAC. This was not an issue when I was just using iTunes to send to the AppleTV. However, PureMusic Player (and probably others) can stream at much higher rates limited only by CoreAudio, which I believe goes to 96/24


You say it is a pass-through device, which implies it can handle 96/24, but can only handle audio files that iTunes can read, which implies 44.1/16 or maybe 48/16. So, which is it? If the former, this device can solve my problem. If the latter, I may as well stick with the AppleTV.

Jul 1, 2011 11:37 AM in response to IHaveOne

Sorry for any confusion that I may have introduced.


The audio output on the headphone/line output jack on the Mac is different that the audio output on the AX, specifically on the analog side.


For analog audio, the Mac provides a higher quality output via a 24-bit/44.1-192 kHz DAC. The AX uses a 16-bit Texas Instruments PCM2705 DAC.


For digital audio, I believe the Mac supports both 24-bit stereo with anywhere between a 44.1 to 192 kHz sampling rate. It also supports at least two types of signals: encoded digital audio (aka Dolby Digital and DTS) and two-channel linear PCM, which as you know is just a stereo signal carried digitally over optical fiber.


For the AX, audio input is primarily provided by iTunes. Of course, it can also get input from other sources like Rogue Amoeba's Airfoil.


iTunes does most of the work. When iTunes plays back standard audio content (AAC, MP3, audiobooks, Internet music streams, etc., it decompresses those file formats and creates what's essentially a raw, uncompressed audio stream. That stream is compressed using Apple's Lossless Compression (via a QuickTime codec), encrypted, and then, streamed (via AirTunes/AirPlay) to the AX. The AX decrypts the stream, decodes it, and outputs it in either analog format or as a digital PCM stream.


If iTunes is playing back a digital multichannel file format like AC3 (Dolby Digital) or DTS, those bitstreams (like the lossy formats) are wrapped in Apple's Lossless compression, encrypted, and then, streamed to the AX. In these cases, the AX would first decode the stream, and then, output the raw AC3 or DTS stream via its optical digital audio port.

Jul 1, 2011 1:32 PM in response to Tesserax

Still confused.


I have software that will put a signal on the ethernet line that equals the best the MBP can do. Recent MBPs may go to 192/24, but my 2007 model, at least according to Audio MIDI Setup, seems only to support 96/24. Be that as it may, I am using ethernet out on the MBP at 96/24. The audio output is not used, just the ethernet.


The software I am using is from Channel D. It acts as a music server and uses iTunes as a source of music files, but as far as I have been able to find out it doesn't actually use iTunes in producing its data stream.


Currently, I have an older AppleTV at the end of the ethernet line. It connects over an optical line to my DAC which can also handle 96/24. I am told the AppleTV only handles up to 44.1/16 or 48/16, I'm not clear which. In any event, it is a bottle-neck.


I have now determined the AX can accept input from ethernet and it has an optical output. The question I am still trying to get answered is if it sees 96/24 coming in, does it pass that to the optical output or does it throttle it back to 44.1|48/16? I am not trying to use the DAC in the MBP or the AX. I am just trying to get a digital stream to the DAC in my stereo system.

Does airport express support ethernet input?

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