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Sound Quality Accross Wireless Connection

Discussion in 'Hi-Fi Stereo Systems & Separates' started by danprice, Jul 26, 2004.

  1. danprice

    danprice
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    Hi,

    If I connect my PC wirelessly, using something like Apple's "Airport" device, to a decent amp. will I lose much sound quality. My music on my computer is stored as 192kbps AAC files. Would a wired (optical or coaxial etc) give a much better sound quality?

    Thanks
    Dan
     
  2. nikyzf

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    Hi Dan,

    This is a matter that concerns me too. I think it will be dependent purely on the quality of the DAC in the Airport vs. the DAC you would use with the wired option. If the latter is a hi-fi DAC then I'd expect it to easily out-perform the Airport but I don't know how you'd find out without trying both (or trusting a review of the Airport when one appears).
     
  3. VirusKiller

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    I'm running uncompressed WAVs 1344kbit/s over wireless to a Squeezebox. Granted that the digital output of the S/box is going to a Meridian 518 processor and Meridian 566 DAC, but it sounds stunning.

    I am getting dropouts during playback, but that has nothing to do with the wireless network - there is a memory leak in the Slimserver software under Linux which eats all of my RAM and brings the hard drive swap into play...
     
  4. norderney

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    I am thinking of buying a Squeeze Box.

    You say you are playing back the tracks as uncompressed WAV files.

    What size of hard disk are you using and how many tracks/CDs have you downloaded?

    My preferred option would be to copy my CDs onto my hard disk as uncompressed WAV files, but I am concerned about the amount of disk space I would require.

    I would be looking at copying about 7500 tracks to my PC. I may have to consider the MP3 format set to the max of 320kps.

    I would be feeding the audio from the Squeeze Box through my Arcam A80 amp.

    Glad to hear you like your Sqeeze Box.
     
  5. VirusKiller

    VirusKiller
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    I have only copied a hundred or so albums so far. I've got two 160GB drives, one of which is for backup purposes only (all that time ripping albums is an investment...). I'm about to buy another pair of the same 160GB drives to move total backed-up storage to >300GB. For 7500 uncompressed WAV tracks, you will need the best part of 500GB. Large, but not impossible...

    Joel
     
  6. nikyzf

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    How about using lossless compression like shn, FLAC, or Apple Lossless? No quality loss, but 1/2 the file size (approx). As long as the wireless receiver/DAC can cope with one of these formats, then wouldn't this be the way to go? :)
     
  7. cwick

    cwick
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    Just to point out that the airport express will output PCM via it's optical output, so you're not dependant on it's DACs. It uses Apple Lossless over-the-air (i.e. whatever the source format - AAC, MP3, WAV ...), it's transcoded on the host to ALE, squirted over the air, and the AirportExpress will transcode to PCM, and then onto your DAC (if you're using digital out), or through it's own DAC if you're using it's analogue out.

    No idea how good the result is ... I'll let you know when I've got mine ;)

    Cheers, Carl.
     
  8. nikyzf

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    Please do. :thumbsup: Using Lossless as far as the Airport Express, then having the option of full PCM into an external DAC seems like a winner, especially as it's also a data wireless base station. Wi-fi indeed! :D
     
  9. cwick

    cwick
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    It can also stream 5.1 DD/DTS, should the need arise.

    Good review of it here, although not particularly indepth w.r.t it's sound quality.

    Cheers, Carl.
     
  10. nikyzf

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    Thanks for the link. The review clearly is not by a hi-fi fanatic, but is still very useful. I assume the minijack socket doubles as digital?
     
  11. davehk

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    It depends on what transport protocol is used over the wireless link? UDP/IP or TCP/IP. UDP has no error correction, but TCP has error correction and retransmission. Provided the software is correctly written, you should not get any errors at all over the wireless link without knowing about them. Buffering in the receiving device should take care of latency and jitter caused by any error correction/retranmissions.

    Note that in the case of TCP there is error correction in tranmission of the packetised audio data over TCP/IP network connections; this is totally different to error concealment done in CD players and can have no effect whatsoever on the sound, since it guarantees that there are no errors in the data. So the sound qualilty should be the same as if the link was not there.

    If UDP/IP is used, then if there is no error correction/retransmission at the application layer, CD like interpolation would have to be used if a packet was dropped or corrupted and this would impact the sound quality.
     
  12. nikyzf

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  13. cwick

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    Well, I'll stick my neck out and say that Airport Express is almost certainly using the same mechanism as iTunes playlist sharing ... so that's Rendezvous (a.k.a. OpenTalk, ZeroConf) for service discovery, and DAAP for playlist access, playback etc.

    So that's UDP for discovery, and (yet another) protocol over HTTP (hence TCP) for playback.

    Of course, error correction in TCP alone doesn't guarantee perfect playback - the data may get there eventually, thanks to all those layers that handle error correction and retransmission - but there's a buffer in the Airport Express, and eventually it'll be exhausted. So the music might skip, glitch, pause or whatever. Depends on the reliability of your link.

    My experience with iTunes remote sharing (PC upstairs with iTunes library, PowerBook plugged into AV receiver downstairs, playlists being shared over wi-fi) suggest it'll be just fine, assuming your wireless connection is good. It'll handle the occaisonal loss of signal ok, and when it's flowing freely, it sounds identical to streaming from a local iTunes library.

    But if your wireless is flakey, it's not so fun. I was using a DLink AP, which simply didn't get on with the powerbook. Result ? Playback would skip, glitch and, on a couple of occaisions, the PCM stream was broken enough to actually cause a hard shutdown of the AV receiever. :eek: Really suprised me the first time it happened. Now I'm using a Linksys AP (same wi-fi chipset as Apple kit), and all is well.

    Not sure what my point is now ...

    Cheers, Carl.
     
  14. nikyzf

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    Interesting :) Odd thing is that D-Link make a point of saying many of their products are Mac-friendly, whilst Linksys don't, or at least not to the extent that I've noticed. BTW DYK that Linksys are part of Cisco?
     
  15. cwick

    cwick
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    Finally got the Airport Express, and it works pretty well. Setup was very simple. I'm not using it as an access point, just a WiFi client purely for AirTunes. It needs SSID broadcast enabled on the AP to join initially though, but things went swimmingly after that.

    Sound quality wise, I'm pretty impressed so far. Only using it's analogue outputs while I wait for a suitable optical cable to arrive, but it certainly doesn't sound bad. Will report back once I've got it properly hooked up (it'll be running through a DAC and then onto the Amp).

    Listened for most of the evening and didn't get any significant dropouts. Only once did I hear a problem - turned on a cheapo light used to backlight the plamsa, which always causes dropouts on FreeView, and there was a corresponding skip in the music - like it missed a beat. No harsh noise though, or dodgy digital dropout type sound I'm used to with FreeView reception issues, just a slight hiccup in the playback. So not too shabby. Will be interesting to see what happens with the digital signal in the same circumstances.

    But it's already a keeper. For me, controlling the stereo using iTunes from a laptop on the sofa beats wandering over to the CD tower and hunting out the tune you're looking for hands down ;)

    Cheers, Carl.
     

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