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Discussion Starter #1
Is there any way to get iPod to output PCM in digital format? I would like to use a high quality DAC for my system.


Larry
 

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No. There you can use the analog outs to stereo l/r; but there's no way to get to the digital signal, unless someone could physically open the thing up and connect to something internally (even then you'd probably have to add a chipset or something). Maybe in the future Apple will offer this, but they haven't given any indication so far.
 

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FWIW you can play your iTunes library thru an Apple Airport Express WiFi module as it has a mini Toslink output.
 

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Hey, I didn't know that; so you connect the iPod to the AirportExpress via Firewire or USB 2.0, then? So that bypasses all DAC's in the iPod. Hmm, interesting. Airport Express is basically a wireless router, correct?
 

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Discussion Starter #6
I must be dreaming - if I fix up the music with EAC (see link below), the digital link will provide an input to my DAC so that I can have very high sound quality.


Question: is the Toslink sending out PCM?

http://www.exactaudiocopy.de/
 

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Yes...it is sending PCM...BUT....what the iTunes/Airport Express combo does is convert the MP3 to AAC first...and then to PCM.


I switched to a SqueezeBox and it made an audible difference in sound quality, and it is a much more robust piece of hardware....but also more expensive.

http://www.slimdevices.com/index.html
 

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Discussion Starter #8
Quote:
Originally Posted by cschang
Yes...it is sending PCM...BUT....what the iTunes/Airport Express combo does is convert the MP3 to AAC first...and then to PCM.
If I use EAC with no compression to create a WAV file, would I still lose sound quality?


If that works, looks like all I need to do is to connect the iPod to the AirPort Express with the USB cable, then connect the Toslink from the AirPort Express to a DAC. Finally, connect the DAC to my system.
 

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Quote:
Originally Posted by fulusu
If I use EAC with no compression to create a WAV file, would I still lose sound quality?


If that works, looks like all I need to do is to connect the iPod to the AirPort Express with the USB cable, then connect the Toslink from the AirPort Express to a DAC. Finally, connect the DAC to my system.
I think you should research that. I am almost positive the Airport Express does NOT offer hardwire connectivity to the iPod.
 

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Yes the USB port on the airport express is for connecting a printer to allow you to wirelessly print from any computer on your network. This unit works very well and the sound quality is very accpetable as long as your source material is of good quality.


Here is a pretty good article on the audio aspect of the airport express

http://stereophile.com/accessoryreviews/505apple/
 

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Quote:
Originally Posted by Enigma
Hey, I didn't know that; so you connect the iPod to the AirportExpress via Firewire or USB 2.0, then? So that bypasses all DAC's in the iPod. Hmm, interesting. Airport Express is basically a wireless router, correct?
Well, I wasn't thinking of connecting the iPod directly to the AE. I'm not sure if you could stream from an iPod via the USB. I was thinking that since the iPod would require that you have a music library on a computer to sync to, you could easily stream the contents of that library. It's not really what the poster asked to do, but it's a workaround.


Also for folks with non-Apple solutions, I would think you should be able to do the same thing with the non-AAC library on your computer and some other third party media access point such as Roku (provided that the DRM is dealt with accordingly).


Yeah, AE can be a base station or a relay or a print hub... all sorts of things. I use mine to digitally stream music to the living room as well as connect the xbox to the internet. It's small and portable too... I take it on trips for hotels that have ethernet but no WiFi.


Regards,

JnC
 

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Quote:
Originally Posted by cschang
Yes...it is sending PCM...BUT....what the iTunes/Airport Express combo does is convert the MP3 to AAC first...and then to PCM.
What you say is technically correct, but the AAC it is using to send over the network is Apple Lossless format, which is not the same as most common AAC codecs, which are lossy. So there should not be any sound quality loss from the format conversion as you imply.


If you look at the stereophile link elsewhere in this thread, they confirm through measurement that 1) the Airport Express' digital output is very good and 2) it is bit for bit identical to the input file.
 

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the airport express has two audio outputs. They both run over the same jack.


one output is standard analog output 3.5mm stereo jack that you can plug into RCA jacks on your receiver. Their comments are that this is pretty good, although it has some jitter noise.


the other output is toslink digital output which they rate as very good, providing bit-for-bit identical output from the input signal and very low jitter as well.


they don't get into this, but the process by which this device works is:

1) iTunes on Mac/PC reads input file (could be mp3, aac, wav, aif, apple lossless, etc.)

2) iTunes transcodes to apple lossless, applies encryption, etc.

3) iTunes sends over network to Airport Express

4) Airport Express decodes/decrypts audio stream to PCM digital

5) Airport Express sends PCM digital out via Toslink to receiver


The stereophile article tests and confirms that the PCM digital output of the Airport Express (APX) is bit-for-bit identical to an input .wav file and thus, the Airport cannot be blamed for any sound quality loss when the digital output is used. Analog outputs is a different story and that can be argued in terms of comparing versus other devices.


If one uses the APX this way, the ideal format for storing your audio files is actually Apple Lossless format, since this uses 50% of the storage space as WAV and does not lose any sound quality. (you could use your EAC wavs as input to convert to Apple Lossless)


Also, since it is the same format that iTunes uses to send over the network, one could argue that it may take less CPU resources on the server since it does not need to transcode. (I have not tested this, however)
 

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Also, the article mentions a time lag at the beginning of songs if a new selection was made, but with the last update of iTunes this has been fixed.
 

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i forgot to mention that this is the only way to play songs purchased from the iTunes music store without directly connecting your computer, or stripping the DRM.
 

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Thanks Collin.


Two things:


Isn't that test only valid for WAV files because other files were not tested.


Also, does converting the Apple Lossless and they transmitting create more network traffic or processing overhead?


The later is one of the things I like with the Squeezebox....MP3 stays MP3 during the network transfer.
 

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well, the test really can only be done with wav or aif because those formats are basically PCM digital on disk and do not need decoding before sending to the d to a converters. all the other formats are basically decoded to PCM digital as an intermediate step before conversion to analog by the DA converters. Since the intermediate step's data is not exposed to the user, its difficult to make a true comparison. However, it would make logical sense that if the PCM formats (wav, aif) are transmitted with bit for bit accuracy, then the lossy formats (mp3, aac) which are converted to PCM then before undergoing the same process would also be transmitted accurately.


Yes, converting to Apple Lossless does incur more processing overhead to do the conversion, and does create more network traffic as compared to sending the lossy formats, but less than sending uncompressed PCM data. However, both the conversion and the transmission seem to be handled without breaking a sweat by modern computers and networks.


The advantage of the way Apple does it with the iTunes/Airport Express combo is that it can support any codec supported by iTunes, which is software. If Apple decided to add OGG or FLAC support to iTunes, then suddenly the Airport Express would support it too. Or, if an improved MP3 decoder is available, then the improvement is gained without changing the hardware through a firmware update, etc.
 

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I use my Airport Express mostly for wireless streaming of my music from my PowerBook while I surf on the couch. It works seamlessly. I also connect my iPod from time to time.


There's a clear difference between using a mini plug to RCAx2, the dock connector to RCAx2, or the AE. Of course, the codec and bit rate make a big difference that matters a lot in the house but not at all in the car or in the gym.
 

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Keep in mind the APX only allows use of either the analog outs or digital outs, not both silmultaneously. If you plan to use a multi zone AVR/pre-pro with toslink feeding the main zone and analog feeding Z2, you are out of luck with the APX.
 
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