Streaming Hirez via Airport Express? Is it really possible?

[treefrog13]

There is so much contradictory information on this and other sites that I need to come back to this topic. Is it really possible to stream hirez music data via Airport Express? People report doing it, but have they ever checked what's really coming out of Airport's S/PDIF?

The setting: I have a lot of hirez AIFFs (24/88.2 and 24/96) recorded from my vinyl and I want to stream them unaltered to the DA-converter of my music system that accepts TOSLINK optical inputs from Airport base station's TOSLINK output. The files reside on my intel iMac where I play the files either by Amadeus Pro or by Bias Peak Pro. Airfoil is set to "Pure Playback" for streaming the music to the Airport base station's S/PDIF-TOSLINK and the music plays nicely on my system.

However, when I checked the digital format of the stream arriving at Airport base station's digital output, I discovered that the stream is in 16/22.05. This is not identical to the format of the original AIFF.

My question is: at which point on the way from the original files to Airport's output are the files being converted from 24/96 to 16/22.05?

(a) Is it the program (Amadeus Pro or by Bias Peak Pro) playing the files that does the conversion to 16/22.05?
(b) Is it Airfoil (although it is set to "Pure Playback")?
(c) Or is it at the Airport client's (i.e. my iMac's) conversion to the IEEE 802.11g protocol that sends only 16/22.05 formats? IEEE 802.11g has enough bandwidth to stream 5.1 DTS signals. So it should be able to handle stereo 24/96 signals.
(d) or could it be somewhere else I didn't think of (e.g. in the Audio/MIDI setup)?

If one of these is the reason for the conversion, how can this be remedied to really stream 24/96 coding?

If there is no such remedy, then why would I need Airfoil instead of iTunes that does the same?

 

[superbovine]

My question is: at which point on the way from the original files to Airport's output are the files being converted from 24/96 to 16/22.05?


(a) Is it the program (Amadeus Pro or by Bias Peak Pro) playing the files that does the conversion to 16/22.05?

I do not know the answer to this question.

(b) Is it Airfoil (although it is set to "Pure Playback")?

Probably not. Airport Express uses encryption technology. The reason why Airfoil is called "foil" is because the guy who cracked the dvd encryption cracked this one, and this company used it in their software called "Airfoil" since it foiled the encryption of the Airport Express/iTunes. If I remember correct, to send the stream of music to the airport express it requires you to down-convert the stream and encryption hence the change in your playback.

(c) Or is it at the Airport client's (i.e. my iMac's) conversion to the IEEE 802.11g protocol that sends only 16/22.05 formats? IEEE 802.11g has enough bandwidth to stream 5.1 DTS signals. So it should be able to handle stereo 24/96 signals.

IEEE 802.xx just wraps the data it doesn't convert the data, your wireless router will strip the extra data once it arrives. However, that being said:

In the consumer (home-theater) market, AC-3 and DTS are closer in terms of audio performance. When the DTS audiotrack is encoded at its highest legal bitrate (1.5 MBps), most technical experts regard DTS as achieving perceptual transparency (i.e. indistinguishable to the uncoded-source in a double-blind test.) At AC-3's maximum bitrate of 640 Kbps, Dolby claims similar transparency. However, the DVD format limits AC-3 audiotracks to 448 Kbps, and some publishers limit the AC-3 bitrate further (to 384 Kbps.) Even at 448 Kbps, (DVD) AC-3 operates at a higher bitrate than theatrical (35 mm movie) AC-3, therefore a properly-equipped home-theater already achieves surround sound superior to a cinema AC-3 installation. Likewise, DTS-audio on movie DVDs is commonly encoded at a reduced bitrate, allowing a single title to fit multiple 5.1 soundtracks (AC-3 + DTS.) At this reduced rate (769 Kbps), DTS no longer retains audio-transparency.

The network latency is to high to stream anything that high wirelessly hence why you see DVD players have optical audio cables. Not to mention latency on a wireless network is unpredictable due to outside factors and distance from the router etc. The problem increases once you try and sync 5.1 with video. Also remember DTS is small, raw 5.1 is huge amount of bandwidth. even if you had it the bandwidth airport express would still buffer the audio which would make video and audio out of sync again.

basically, it wasn't design to do what you want it to do. the cpu/ic is probably not fast enough to handle 5.1, if it was design for it they would included hardware that every 5.1 receiver has in it to process digital audio.

(d) or could it be somewhere else I didn't think of (e.g. in the Audio/MIDI setup)?

no, the problem is in the airport express itself.

If one of these is the reason for the conversion, how can this be remedied to really stream 24/96 coding?

If there is no such remedy, then why would I need Airfoil instead of iTunes that does the same?

no and no.

 

[treefrog13]

Thanks a lot, Superbovine. Very helpful.

 

[DudeDah]

So then...

I have some Apple lossless files that came from a DTS encoded audio disc that is supposed to have the DTS intact. How can I play these files on my mac. iTunes? Somthing else? And so are you saying these files can't be sent (and play correctly) to my DTS receiver via AX through my TOSLINK cable. Sorry for the newb questions but right now all I am hearing is static, white noise, whatever the correct term is. THANKS!!

 

[superbovine]

I have some Apple lossless files that came from a DTS encoded audio disc that is supposed to have the DTS intact. How can I play these files on my mac. iTunes? Somthing else? And so are you saying these files can't be sent (and play correctly) to my DTS receiver via AX through my TOSLINK cable. Sorry for the newb questions but right now all I am hearing is static, white noise, whatever the correct term is. THANKS!!

did you read the thread, it was about the airport express?

 

[DudeDah]

did you read the thread, it was about the airport express?

Ok...I'm not sure if you are patronizing me or just addressing ONE ASPECT of my question/situation. Yes, I read the thread and it appears that AX is not going to work.

How can I play these files on my mac. iTunes? Something else?

Any OTHER helpful suggestions? Burn these DTS encoded files to a disc and play them that way? Third-party media player?

 

[superbovine]

Ok...I'm not sure if you are patronizing me or just addressing ONE ASPECT of my question/situation. Yes, I read the thread and it appears that AX is not going to work.

don't take it personally, usually ppl post new topics in a different thread.

https://forums.macrumors.com/threads/105963/
https://forums.macrumors.com/threads/67843/

 

[weldon]

The Pure Playback setting in the Airfoil means that it won't alter the timing of the signal to try and keep multiple Airport Express clients in synch. The Airport Express is still only expecting CD-quality digital audio though and that's what it sends. Airfoil encodes other audio sources to the same signal as CD audio so that the Airport Express will recognize it just like it would if iTunes were encoding MP3 files to CD audio for AirTunes.

 

[DudeDah]

don't take it personally, usually ppl post new topics in a different thread.

I apologize, I thought it was related enough as to not merit a full hijack.